Fruit & Vegetable Fertiliser | Organic Plant Food 4-5-6
A balanced 4-5-6 feed for fruit and veg.
from £11.50
Tomato Fertiliser — 3-4-6 NPK, 16 organic ingredients, designed for flavour
3-4-6 NPK
16 Ingredients
Flavour Focused
Slow Release
Full Ingredient Transparency
Handmade in the UK
Most tomato fertilisers are designed around yield. This one is designed around taste. The 3-4-6 NPK ratio — with potassium at twice the nitrogen level — is the result of over 30 years of research into what makes tomatoes sweet, aromatic and complex. Sixteen premium ingredients including Yorkshire Polyhalite, Scottish Seaweed Meal, British Biochar and Dried Worm Castings deliver a complete slow-release feed that builds the soil as it feeds the plant. Handcrafted in Stockport.
The 2:1 K:N ratio is the single most important nutritional lever for fruit quality. It drives sugar loading into fruit, stimulates lycopene synthesis, and activates the enzymatic pathways for the volatile aromatic compounds that give tomatoes their scent. Peer-reviewed meta-analysis of 313 studies confirms organic fertiliser produces 72% more aroma volatiles and 24% more lycopene than mineral alternatives.
3-4-6NPK Ratio
16Premium Ingredients
+72%More Aroma Volatiles*
2:1K:N Ratio
*Zhang et al. (2023), meta-analysis of 313 studies. See The Science tab.
What this formula does for your tomatoes
- Sweeter, more complex flavour — chloride-free potassium at twice the nitrogen level drives sugar translocation from leaf to fruit, the primary mechanism of Brix, sweetness and flavour intensity
- Deeper colour, more lycopene — high K and sulphur from Yorkshire Polyhalite stimulate carotenoid biosynthesis, the pathway responsible for both red pigmentation and the carotenoid-derived volatiles that define tomato aroma
- No blossom end rot — calcium built into the formula from multiple sources provides the continuous supply that prevents cell wall failure in developing fruit
- Living soil biology — British Biochar and Dried Worm Castings introduce beneficial microorganisms that suppress pathogens through competitive exclusion and produce secondary metabolites linked to improved flavour
- Trace mineral depth — seaweed, basalt rock dust, polyhalite and clay minerals supply zinc, iron, manganese, boron and copper — the enzyme cofactors required to synthesise aroma volatiles
- Lower nitrate in fruit — slow-release organic nitrogen arrives at a rate the plant can fully utilise, producing 30–50% lower nitrate than mineral-fed fruit with cleaner, less bitter taste
Dr Forest Tomato vs liquid tomato feed
Dr Forest Tomato Fertiliser 3-4-6
- 16 ingredients — full nutritional picture including calcium, sulphur and trace minerals
- Living biology: fermented biochar + worm castings + EM microorganisms
- Slow-release organic fractions feed for weeks per application
- Every application permanently improves the growing medium
- No salt accumulation, no EC spike, no chloride
- Apply every 2–4 weeks — not weekly
Typical Liquid Tomato Feed
- 3 nutrients — NPK and nothing else
- No calcium — the nutrient that prevents blossom end rot is absent from virtually all liquid tomato feeds
- No living biology — soluble salts suppress beneficial soil organisms
- Feast-and-famine cycle — dissolves within hours, leaches by next watering
- Adds nothing to soil structure, biology or long-term fertility
- Salt and EC build-up in containers and grow bags
- Weekly dosing required throughout the season
Handcrafted in Stockport
Dr Forest fertilisers are blended in small batches from traceable British ingredients. Named after Joe's grandfather — an NHS GP who believed in doing things properly. No shortcuts. Every bag is made to the same standard we use in our own garden.
All 16 ingredients — what they do and why they are in the formula
Every ingredient is here for a specific, research-backed reason. Nothing is filler. The potassium mineral is mined in North Yorkshire. The seaweed is hand-harvested from Scottish waters. The biochar is British-sourced and fermented before blending.
01
Yorkshire Polyhalite — 🇬🇧 North Yorkshire · Slow release
Supplies four nutrients from a single crystal: K, Ca, Mg and S. Mined 1,200m below the North Sea. The sulphur fraction directly increases total soluble solids (Brix) in tomatoes — a benefit absent from most organic tomato fertilisers. Releases over 50–60 days, providing sustained background nutrition without salt spikes. Johnston & Dawson, 2018
02
Sulphate of Potash (SOP) — Mineral · Immediate release
Fast-acting potassium at 50% K₂O — chloride-free. Activates sugar translocation from leaf to fruit, lycopene synthesis and anthocyanin production immediately. Chloride at high concentrations interferes with lycopene synthesis; no muriate forms are used anywhere in this formula. Römheld & Kirkby, 2010
03
Micronised Magnesium Mineral — Mineral · Sustained release
Magnesium is the central atom of every chlorophyll molecule — without it, the photosynthesis that produces fruit sugars fails. At 20.9% Mg and 5-micron particle size for rapid uptake. Provides sustained correction for UK soils chronically deficient in Mg. Marschner, 2012
04
Nitrogen Plant Extract — Plant-derived · Controlled release
Fast-release organic nitrogen for early vegetative establishment. Plant-derived, mineralising through microbial protease activity without the nitrate spikes associated with synthetic N sources. The controlled-release profile prevents excess nitrogen redirecting energy into foliage at the expense of fruit. Marschner, 2012
05
Phosphorous Plant Meal — Plant-derived · Fast–moderate release
Organic phosphorus for root development, energy transfer and fruit set. Undergoes rapid microbial breakdown, releasing P within weeks at the two most critical moments: root establishment after transplanting and bud initiation at flowering. Marschner, 2012
06
Rapeseed Meal — 🇬🇧 British · Slow release
High-protein seed meal providing steady nitrogen over 6–8 weeks through microbial protease breakdown. Acts as a prebiotic carbon source for the soil microbial community. The gradual mineralisation avoids the nitrate spikes that suppress fruit set and dilute flavour. Jensen, 1994
07
Scottish Seaweed Meal — 🏴 Hand-harvested
Trace minerals, natural auxins and cytokinins, and alginates for soil structure and stress tolerance. Over 60 trace elements including zinc, iron, manganese and boron — many directly involved in the biosynthesis of volatile aromatic compounds. Craigie, 2011
08
Seaweed Extract — British coastal · Biostimulant
Concentrated biostimulant supplying cytokinins that delay fruit and leaf senescence — extending the productive season. Enhances nutrient uptake, flowering and fruit-set under stress. Betaines improve osmotic adjustment under drought. Craigie, 2011
09
Alfalfa Meal — Plant-based · Slow release · Biostimulant
Contains triacontanol — a natural plant growth regulator that increases chlorophyll content by 15–20% and accelerates meristematic cell division. Increases photosynthate production and partitioning to developing fruit. Khan et al., 2009
10
British Biochar — 🇬🇧 Fermented · Activated
Creates a permanent, porous carbon scaffold housing beneficial microorganisms. Increases plant-available K retention by 18–35% under leaching conditions — particularly valuable in grow bags and containers. Fermentation activates the surface with beneficial microbial populations before application. Lehmann et al., 2011
11
Humic Acid — Mineral organic · Chelation
Chelates micronutrients — particularly iron and manganese — maintaining them in plant-available form across a wide pH range. Increases total soil bacterial biomass by 30–60% and stimulates mycorrhizal colonisation by 25–40%. Nardi et al., 2009
12
Dried Worm Castings — Living biology · Bioavailable nutrients
A single gram contains hundreds of millions of beneficial organisms. Supplies nutrients in immediately plant-available form while introducing bacteria, fungi and protozoa that activate within days. Worm casting-enriched soil consistently produces fruit with improved flavour and higher Brix even at identical NPK levels.
13
Silica Meal — Mineral · Structural
Silicon strengthens epidermal cell walls — a physical barrier against aphid stylet penetration, thrip rasping and fungal spore germination. Improves stem rigidity, reducing collapse under heavy truss load. Epstein, 1999
14
Clay Minerals — 🇬🇧 British · Permanent CEC reservoir
Montmorillonite and illite clays with the highest cation exchange capacity of any soil mineral — ionic reservoirs that bind and slowly release K, Ca and Mg between waterings. Clay CEC is permanent. Barker & Pilbeam, 2015
15
Volcanic Rock Dust (Basalt) — Mineral · Trace elements
Broad-spectrum trace elements: zinc for alcohol dehydrogenase activity, iron and copper for oxidative cleavage of carotenoids, manganese for antioxidant enzyme systems. These are the enzyme cofactors required for aroma volatile biosynthesis.
16
Herbal Mixture — Plant-derived · Biostimulant
Plant-derived biostimulants supplying secondary metabolites that enhance microbial activity and plant resilience. Broad-spectrum biological stimulus for the soil microbial community. Zaller & Kopke, 2004
How to use tomato fertiliser: rates, timing & method
Measuring made simple
This product is a milled powder with a bulk density of 1 g/ml — grams and millilitres are interchangeable. You can measure by weight on a kitchen scale or by volume using a measuring jug or spoon. 3 level teaspoons = 1 tablespoon ≈ 15 ml. For best results, mix with an equal volume of compost before applying.
Step-by-step: containers and grow bags
- Prepare your potting mix. Measure 5–10g per litre of compost. 5g/L for mixes already containing nutrients; 10g/L for plain or peat-free compost. Mix thoroughly for at least two minutes to prevent localised hot-spots.
- Fill your container and plant. Leave 5cm headspace for watering. Set the plant at the correct depth. Firm gently. If planting into an existing container, mix the fertiliser into the compost before transplanting.
- Water in thoroughly. Water until it runs freely from drainage holes. This activates the slow-release process. Do not allow the pot to dry completely — organic nutrient release is moisture-dependent.
- Wait 10–14 days before first top-dress. The initial potting mix dose provides nutrition for the first two to three weeks. Begin top-dressing once plants show new growth.
- Top-dress every 2–4 weeks. Apply 1–3g per litre of pot volume in a band around the outer rim, 10cm from stem. Lightly scratch into the top 2–3cm. Water immediately.
- Adjust based on plant signals. Pale yellowing lower leaves: increase to fortnightly or move toward 3g/L. Excessively dark green foliage with few flowers: stretch to every 4 weeks and reduce toward 1g/L.
Application rate table
Containers & pots
| Situation | Rate (g = ml) | Frequency | Notes |
|---|---|---|---|
| Potting mix preparation | 5–10g per litre of compost | Once at potting | 5g/L in enriched mixes. 10g/L in plain or peat-free compost. |
| Container top-dressing | 1–3g per litre of pot volume | Every 2–4 weeks | 1g/L for established plants. 2–3g/L for large containers (20L+) or peak fruiting. |
Outdoor beds & raised beds
| Situation | Rate (g = ml) | Frequency | Notes |
|---|---|---|---|
| Bed preparation | 150–200g per m² (up to 250g for depleted soil) | Once before planting | Fork into top 10–15cm. Preparing 2–4 weeks in advance allows nutrients to begin releasing. |
| Outdoor top-dressing | 75–150g per m² | Every 2–4 weeks | 75g/m² in fertile soil during vegetative growth. 100–150g/m² during peak fruiting. |
| Single plant at transplanting | 30–45g per plant | Once at planting | Mix into planting hole with equal volume of soil or compost. 10cm gap from stem. |
| Single plant top-dressing | 30–45g per plant | Every 2–4 weeks | Ring around the plant 10–15cm from stem. Lightly scratch in. Water in thoroughly. |
Seasonal feeding guide
| Stage | Timing | Rate & Frequency | Goal |
|---|---|---|---|
| Bed preparation / potting mix | 2–4 weeks before planting | Beds: 150–200g/m². Pots: 5–10g/L compost | Build nutrient-rich root zone before the plant arrives |
| Transplant establishment | At planting | 30–45g per plant into planting hole | Localised nutrient boost for rapid rooting |
| Early vegetative growth | 10–14 days after transplanting | 75g/m² or 1g/L every 3–4 weeks | Healthy structure without excessive N-driven bulk |
| Active flowering & fruit set | First flowers through heavy fruit load | 100g/m² or 2g/L every 2–3 weeks | K and P support for flower retention and fruit set |
| Peak fruit fill | Heavy green fruit on all trusses | 150g/m² or 3g/L every 2 weeks | Maximum demand — sugar loading and lycopene synthesis |
| Ripening & late season | Once fruit begins to colour | Lower range or skip; every 3–4 weeks | Concentrate sugars and volatiles; ease off nitrogen |
Works well combined with…
Use Dr Forest Seaweed Powder as a fortnightly foliar — adds cytokinins and trace minerals without extra nitrogen. Apply Dr Forest Liquid Gypsum as a root drench if blossom end rot appears mid-season. Use the Dr Forest All-Purpose 6-6-6 during early vegetative establishment before switching to this formula at first flower.
Tomato growing guide — varieties, training, watering & feeding by type
Not all tomatoes grow the same way, and not all respond to the same feeding and training approach. This guide covers the practical differences between the main variety types grown in the UK — and how to adjust your fertiliser programme, watering, and management to get the best from each one.
The two growth habits: indeterminate vs determinate
Every tomato variety falls into one of two fundamental growth categories. Understanding which you are growing is the single most important decision for training, feeding and watering.
Indeterminate (cordon / vine)
- Grows continuously from a single stem — will not stop until killed by frost
- Requires staking, support and regular side-shooting (removing axillary shoots)
- Produces trusses sequentially up the stem — harvests over a long season
- Most greenhouse and polytunnel varieties are indeterminate
- Higher total yield but spread across months
- Needs consistent feeding throughout the season as new trusses form
- Common UK varieties: Gardener's Delight, Sungold, Moneymaker, Ailsa Craig, San Marzano, Costoluto Fiorentino
Determinate (bush)
- Grows to a genetically fixed size, then stops and sets fruit all at once
- Does not need staking in most cases — may need support once fruit is heavy
- Do not remove side-shoots — each side-shoot produces a truss
- Produces a concentrated harvest over 3–5 weeks rather than months
- Ideal for outdoor growing, patio containers and hanging baskets
- Needs a strong single feed at planting then lighter maintenance feeding
- Common UK varieties: Roma, Tumbling Tom, Totem, Red Alert, The Amateur, Maskotka
Semi-determinate varieties
A few varieties — notably some paste types — are semi-determinate: they grow to a moderate height (90–120cm), set most of their fruit, then slow substantially without stopping completely. Treat these as indeterminate for training (stake and side-shoot) but feed on the lighter determinate schedule once the majority of trusses have set.
Feeding adjustments by variety type
The 3-4-6 formula is designed for all tomatoes, but the feeding schedule benefits from adjustment depending on what you are growing. The differences relate to fruit size, season length and the metabolic demands of different growth habits.
Cherry & cocktail — Sungold, Gardener's Delight, Sweet Million, Tumbling Tom
Small fruit with naturally high Brix. Excessive feeding pushes vegetative growth at the expense of flavour. Light and consistent is better than heavy and infrequent. These varieties already concentrate sugars efficiently — overfeed and they produce leaf, not fruit.
Standard / medium — Moneymaker, Ailsa Craig, Alicante, Shirley
The classic UK greenhouse tomato. Reliable and responsive to the standard feeding schedule. These are the varieties the 3-4-6 ratio was primarily calibrated against. Standard rates, standard timing — follow the How to Use tab directly.
Beefsteak & large-fruited — Brandywine, Costoluto Fiorentino, Marmande, Coeur de Boeuf
Large fruit means high total mineral demand per fruit. Calcium is critical — BER risk is highest in beefsteak varieties because the expanding cells at the blossom end are growing the fastest. Water consistently. Feed at the upper end. Consider supplemental foliar calcium during rapid fruit expansion.
Plum & paste — San Marzano, Roma, Amish Paste, Giulietta
Paste varieties are bred for high dry matter and low water content — exactly what the 3-4-6 K-led formula supports. Slightly less frequent feeding suits their naturally concentrated fruit. These respond exceptionally well to the low-N, high-K approach — Brix improvements are often the most dramatic in paste types.
Bush / determinate — Totem, Red Alert, The Amateur, Maskotka, Tumbling Tom
These set most fruit at once rather than sequentially. Give a strong initial potting mix charge (8–10g/L) then lighter top-dressing (1–2g/L). Reduce or stop feeding once the majority of fruit is set — the plant is winding down, not gearing up. Continued heavy feeding after fruit set produces leaf, not better fruit.
Heritage & heirloom — Brandywine, Black Krim, Green Zebra, Tigerella, Costoluto
Heritage varieties have retained the genetic capacity for complex flavour that modern commercial varieties have been bred out of. They respond more dramatically to potassium-rich organic feeding than any other group — the flavour improvement from 3-4-6 is most pronounced in these varieties. Often larger-fruited, so calcium attention applies.
Greenhouse vs outdoor — what changes
Greenhouse & polytunnel
- Longer season — typically late April transplant through to October
- Higher temperatures accelerate both growth and nutrient demand
- Indeterminate varieties can produce 8–12 trusses under glass vs 4–6 outdoors
- Feed at the upper end of the range and at the shorter frequency (every 2 weeks during peak)
- Ventilation is critical — stagnant humid air promotes Botrytis and leaf mould
- Water in the morning to allow foliage to dry before evening
- Blossom end rot risk is higher because greenhouse temperatures drive rapid transpiration
Outdoor growing
- Shorter season — transplant late May (after last frost), harvest July to September
- Choose early-maturing varieties: Sungold, Gardener's Delight, Red Alert, Tumbling Tom
- Determinate varieties are generally more reliable outdoors than indeterminate
- Feed at the mid-range and standard frequency (every 3–4 weeks)
- Rain washes nutrients through the root zone — the organic fractions in this formula resist leaching far better than liquid feeds
- Outdoor tomatoes often have superior flavour to greenhouse fruit — UV stress increases lycopene and volatile production
- Stop indeterminate outdoor varieties at 4–5 trusses to ensure fruit ripens before autumn
Watering — the make-or-break factor
More tomato problems are caused by inconsistent watering than by any fertiliser deficiency. Erratic moisture — alternating drought and deluge — causes blossom end rot, fruit cracking, poor calcium uptake and uneven ripening. The goal is consistent, deep moisture at the root zone.
01
Containers & grow bags
Water daily in warm weather, twice daily in heatwaves. Water slowly until it runs from the base. Never let compost dry completely — once peat-free compost dries out it is very difficult to re-wet evenly. In grow bags, consider burying a plastic bottle with the base cut off next to each plant as a watering funnel — this delivers water directly to the root zone rather than running off the surface.
02
Raised beds & open ground
Water deeply 2–3 times per week rather than little and often. Shallow daily watering encourages surface roots; deep infrequent watering drives roots down where moisture is more stable. Mulch heavily with compost, straw or grass clippings to a depth of 5–8cm — mulch reduces evaporation, buffers soil temperature, and maintains the consistent moisture that prevents BER.
03
Greenhouses
Water in the morning — wet foliage overnight invites fungal disease. Aim to keep the compost or soil at a consistent 60–70% moisture. Drip irrigation on a timer is the most reliable method under glass. In polytunnels, overhead watering is acceptable outdoors but avoid wetting foliage under cover. Ventilate well after watering to reduce humidity.
The calcium connection
Calcium is delivered to fruit exclusively via the transpiration stream — water moving from roots through stems to leaves and fruit. When transpiration is disrupted by drought stress, calcium delivery to the fastest-growing cells at the blossom end of the fruit stops. This is why blossom end rot is a watering problem as much as a nutrition problem. The calcium in this formula can only prevent BER if watering is consistent.
Training indeterminate (cordon) varieties
- Stake or string at transplanting. Insert a sturdy cane or tie a string from the greenhouse roof before the plant needs it. Trying to support a heavy, floppy plant later risks stem damage and root disturbance.
- Remove side-shoots weekly. Axillary shoots appear in the angle between the main stem and each leaf. Pinch them out when small (5–8cm) using your thumb and forefinger. Removing them when they are larger wastes the plant's energy and creates a bigger wound. Check every 3–4 days during rapid growth.
- Stop the plant at the right time. In a greenhouse, allow 6–8 trusses before pinching out the growing tip — this is typically in late July or early August. Outdoors, stop at 4–5 trusses by early July to give fruit time to ripen before autumn. Stopping redirects all remaining energy into ripening the existing fruit rather than producing more that will not mature.
- Remove lower leaves progressively. Once the lowest truss has been picked, remove all leaves below it. This improves airflow, reduces humidity around the base of the plant, and helps prevent Botrytis and soil-splash diseases. Do not remove more than three leaves in a single session.
- Tie in as the plant grows. Loosely tie the stem to the support every 20–30cm as it grows. Use soft twine or commercial plant clips — never wire. The tie should support, not constrict. Leave room for stem expansion.
UK seasonal timeline
| Month | What to Do |
|---|---|
| February–March | Sow seed indoors on a warm windowsill or heated propagator at 18–21°C. Use a fine seed compost. Do not sow too early — leggy seedlings perform worse than sturdy ones sown later. |
| April | Pot on seedlings into 9cm pots when they have their first true leaves. Harden off gradually if growing outdoors. Prepare greenhouse beds or grow bags with a base charge of Dr Forest Tomato Fertiliser (150–200g/m² or 5–10g/L). |
| May | Transplant into final positions. Greenhouse: late April to early May. Outdoors: after last frost, typically late May in most of England. Apply 30–45g per planting hole. Stake and begin training. |
| June | First flowers appear. Begin fortnightly or three-weekly top-dressing. Side-shoot regularly. Water consistently. The first truss sets — this is when potassium demand begins to increase. |
| July | Peak feeding period — fruit swelling on multiple trusses. Feed every 2 weeks at the upper end of the range. Stop outdoor cordons at 4–5 trusses. Greenhouse cordons can continue to 6–8 trusses. Remove lower leaves below picked trusses. |
| August | First ripe fruit. Reduce feeding frequency to every 3–4 weeks. Ease off watering slightly as fruit colours — mild water stress at this stage concentrates sugars and intensifies flavour. Stop greenhouse cordons at 6–8 trusses if not already done. |
| September–October | Harvest remaining fruit. Green fruit can be ripened indoors on a windowsill or in a drawer with a banana (ethylene). Pull plants once productive life is over. The biochar and organic matter left in the soil will benefit next season's crop. |
Common problems and what to do
Blossom end rot
Water consistently and deeply. Mulch to buffer moisture. This formula includes calcium from multiple sources — supplemental Dr Forest Liquid Gypsum as a root drench can help in severe cases. Remove affected fruit; subsequent trusses usually recover once watering is stabilised.
Fruit splitting and cracking
The fruit skin hardens during drought and cannot expand fast enough when the plant suddenly takes up water. Prevention: consistent watering, mulching, and the strong cell walls that adequate calcium and silicon provide. Pick fruit at first sign of cracking — it will still ripen and is safe to eat.
Yellow lower leaves
If only the oldest leaves are yellowing, the plant is redirecting nutrients into developing fruit — this is normal. If yellowing is widespread or interveinal (veins green, leaf blade yellow), it is likely magnesium deficiency — this formula includes two magnesium sources, but a foliar spray of Epsom salt (10g per litre) provides a quick correction.
Lots of leaf, few flowers
Reduce feeding frequency. Do not add supplemental nitrogen feeds. Ensure the plant is getting 6+ hours of direct sun. In greenhouses, ventilate to prevent temperatures exceeding 30°C — pollen viability declines rapidly above this and fruit set fails. The 3-4-6 K-led ratio is designed to prevent this problem; if it occurs, the plant is being overfed.
Blight (Phytophthora infestans)
Greenhouse growing largely avoids blight. Outdoors, choose blight-resistant varieties (Crimson Crush, Mountain Magic, Fantasio) if blight is recurrent in your area. Remove and dispose of affected foliage immediately — do not compost. The silica and seaweed in this formula strengthen cell walls and prime SAR pathways, providing a degree of structural resistance.
Greenback and uneven ripening
Greenback — hard, green or yellow patches on the shoulder of the fruit that never ripen — is strongly associated with K deficiency and is one of the problems the 3-4-6 high-K formula directly addresses. Ensure leaves shade the fruit from direct sun in greenhouses. This rarely occurs when feeding consistently with a K-led formula.
The science of tomato flavour — and why fertiliser is decisive
Tomato flavour is the result of three chemical systems operating simultaneously inside the ripening fruit: sugars (fructose and glucose, sensed as sweetness), organic acids (citric and malic acid, sensed as sharpness and complexity), and volatile organic compounds (VOCs) perceived as aroma. The balance between these three determines whether a tomato tastes flat and watery or rich, complex and intense.
Of the three, volatiles are the most sensitive to nutrition. A 2023 meta-analysis of 313 studies found organic fertiliser increased aromatic volatile content by 72.1% compared to mineral controls — consistent across dozens of individual trials (Zhang et al., 2023).
Why the 3-4-6 ratio works
The K:N ratio of 2:1 is the single most important nutritional lever for fruit quality. Research across multiple decades consistently identifies a K:N ratio of 1.5–2:1 as optimal for maximising Brix, aromatic volatile production, lycopene synthesis and sensory scores. The 3-4-6 ratio delivers exactly 2:1.
N 3%Low — prevents dilution
P 4%Root & fruit set
K 6%Chloride-free · Flavour driver
2:1K:N ratio
The potassium-flavour connection
K is the primary driver of phloem loading — the transport of sugars from leaves to fruit. Under K deficiency, fruit is lower in Brix, lower in vitamin C, and lower in the volatile compounds that give tomatoes their scent. All K in this formula is chloride-free — SOP and Yorkshire Polyhalite. Chloride interferes with lycopene synthesis.
Key aroma compounds
| Compound | Sensory Character | Nutritional Link |
|---|---|---|
| 6-Methyl-5-hepten-2-one | Classic "tomato" aroma | From lycopene cleavage — proportional to lycopene content; organic produces +24–53% more |
| β-Ionone | Floral, violet, fruity | From β-carotene; enzyme activity depends on iron and copper from trace-mineral-rich inputs |
| Geranylacetone | Fruity, rose-like | From lycopene via carotenoid degradation; enhanced by high-K growing conditions |
| β-Damascenone | Sweet, rose, cooked fruit | From carotenoid precursors; suppressed by excess nitrogen |
| Hexanal & (Z)-3-hexenal | Green, grassy, "just-picked" | Lipoxygenase pathway requires iron and zinc; highest in outdoor soil-grown tomatoes |
Why organic outperforms mineral — the mechanisms
01
Microbial metabolite production
Decomposing organic ingredients produce secondary metabolites — short-chain organic acids, amino acid derivatives and enzyme cofactors — directly involved in volatile organic compound biosynthesis. An organic fertiliser feeds the plant and its entire biochemical environment.
02
Lower nitrate = better taste
Organic nitrogen arrives at a rate the plant can fully utilise. Result: 30–50% lower nitrate in fruit. Cardarelli et al., 2023
03
Trace mineral completeness for aroma biosynthesis
Zinc for alcohol dehydrogenase, iron and copper for oxidative cleavage of carotenoids, manganese for antioxidant enzymes — supplied by seaweed, basalt, polyhalite and clay.
04
Soil biology and disease suppression
Organic fertilisers reduce disease incidence by 45–73% by building the microbial community that outcompetes pathogens. Zhang et al., 2023
05
Carotenoid biosynthesis
Lycopene is the direct precursor to the most important aroma volatiles. Organic systems produce 24–53% higher lycopene. More lycopene means richer colour and more complex aroma. Gao et al., 2023; Hao et al., 2020
06
Gene expression under organic management
All 21 starch and sucrose metabolism genes are upregulated under organic fertilisation — the genetic pathway responsible for sugar accumulation in fruit. Li et al., 2024
07
Combined organic–mineral highest quality
Global meta-analysis of 7,859 data pairs: combined organic + mineral improved yield by ~31% and nutritional quality by ~12%. Wang et al., 2023
08
Long-term soil improvement
Every application adds organic matter, biochar carbon, living microorganisms and minerals. Over successive seasons: increased CEC, improved moisture retention, deeper structure for root penetration, and rising microbial diversity.
Study data: organic fertilisation and tomato quality
| Study | Finding |
|---|---|
| Zhang et al. (2023) — 313 studies, 9,752 observations | +72.1% aroma volatiles, +12% sugars, −16.9% nitrate, −73% disease, +24% lycopene |
| Gao et al. (2023) — 107 studies | +19% vitamin C, +24% lycopene with organic fertilisation |
| Wang et al. (2024) — 67 VOCs measured by GC-MS | Organic: 35.38 μg/g total volatiles — highest across all treatment groups |
| Hao et al. (2020) — greenhouse tomato | +24.1% sugar, +53% lycopene, +129% total carotenoids, +20% yield |
| Javaria et al. (2012) — potassium dose trials | Optimal K significantly increased sweetness, aroma and Brix |
| Tieman et al. (2017) — 398 accessions | 13 key volatiles for consumer preference; modern varieties have lower concentrations |
References
- Barker, A.V. & Pilbeam, D.J. eds. (2015). Handbook of Plant Nutrition, 2nd ed. CRC Press.
- Buttery, R.G. et al. (1987). Fresh tomato aroma volatiles. J. Agric. Food Chem., 35, 540–544.
- Cardarelli, M. et al. (2023). Nitrate accumulation: organic vs conventional. Agronomy.
- Craigie, J.S. (2011). Seaweed extract stimuli. J. Applied Phycology, 23(3), 371–393.
- Epstein, E. (1999). Silicon. Annual Review of Plant Physiology, 50, 641–664.
- Gao, H. et al. (2023). Organic fertilizers and tomato quality. Applied Sciences, 13.
- Hao, X. et al. (2020). Composted organic waste and tomato carotenoids. J. Integrative Agriculture.
- Javaria, S. et al. (2012). Potassium and tomato sensory attributes. Selcuk University.
- Jensen, E.S. (1994). Plant meal N mineralisation. Soil Biology and Biochemistry.
- Johnston, A.E. & Dawson, C.J. (2018). Polyhalite as a fertiliser. Proc. 826, Int. Fertiliser Society.
- Khan, A.A. et al. (2009). Triacontanol. Plant Growth Regulation, 53(3), 203–218.
- Klee, H.J. & Tieman, D.M. (2018). Genetics of fruit flavour. Nature Reviews Genetics, 19(6), 347–356.
- Lehmann, J. et al. (2011). Biochar effects on soil biota. Soil Biology and Biochemistry, 43(9), 1812–1836.
- Li, Y. et al. (2024). Starch/sucrose gene expression under organic management. Nature Scientific Reports.
- Marschner, P. ed. (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press.
- Nardi, S. et al. (2009). Humic substances. Soil Biology and Biochemistry, 34(11), 1527–1536.
- Römheld, V. & Kirkby, E.A. (2010). Potassium in agriculture. Plant and Soil, 335(1–2), 155–180.
- Tieman, D. et al. (2017). Improved tomato flavor. Science, 355(6323), 391–394.
- Wang, Y. et al. (2023). Combined organic–mineral meta-analysis. Science of the Total Environment.
- Wang, Y. et al. (2024). Organic fertilizer effects on tomato VOCs. Frontiers in Plant Science.
- Zaller, J.G. & Kopke, U. (2004). Herbal preparations. Plant and Soil.
- Zhang, X. et al. (2023). Organic fertilizer in tomato quality: meta-analysis. Scientia Horticulturae.
Frequently asked questions about tomato fertiliser
The plant appearance change is gradual — organic slow-release builds soil health over weeks rather than producing the immediate green flush of a liquid nitrogen hit. The difference you will notice most clearly is in the fruit: richer colour, deeper aroma when picked, and noticeably sweeter, more complex flavour. The 72% increase in aromatic volatiles operates through biological pathways that take several weeks to fully activate.
Yes — and this formula is particularly valuable in peat-free compost, which typically has lower initial nutrient levels. Use the higher potting mix rate (8–10g/L) and begin top-dressing after 7–10 days rather than 14. Combining with a liquid seaweed foliar spray every 2 weeks provides strong results.
Excess nitrogen produces large, watery fruit with low Brix, reduced lycopene and minimal volatile production. The 3% N is sufficient for healthy foliage without producing the excess that suppresses fruiting and dilutes quality. If plants show nitrogen deficiency, apply more frequently within the recommended rates rather than adding a high-N feed on top.
Polyhalite is a Yorkshire-mined mineral supplying K, Ca, Mg and S from a single crystal. For tomatoes: K drives Brix and lycopene; Ca prevents blossom end rot; Mg is essential for photosynthesis; S directly increases total soluble solids and is a cofactor for flavour-related enzyme systems. It releases over 50–60 days, providing sustained background nutrition.
Calcium is included to maintain background supply. BER is primarily a water-stress disorder — consistent moisture is as important as calcium. For severe or recurring cases, supplement with Dr Forest Liquid Gypsum as a root drench every 2–3 weeks once fruit is setting. Remove affected fruit; subsequent trusses usually recover once watering is stabilised.
Excellent combination — use the lower potting rate (5g/L) initially to avoid high P inhibiting colonisation. Apply the inoculant directly to roots or into the planting hole. Resume normal rates after 3–4 weeks once networks have formed.
Yes — peppers, aubergines and chillies respond well to the same 3-4-6 ratio. For a wider range of crops including root veg, brassicas and soft fruit, the Dr Forest Fruit & Vegetable 4-5-6 offers a more versatile NPK balance.
Yes — the two are complementary. Dr Forest provides the slow-release foundation; a supplemental liquid seaweed or calcium feed can top up nutrients during peak demand. Avoid replacing the dry base programme with liquid alone.
Yes — see the Growing Guide tab for detailed variety-specific adjustments. Cherry varieties need lighter, less frequent feeding (they concentrate sugars naturally and overfeed produces leaf, not fruit). Beefsteaks need the upper end of the rate range with extra attention to calcium and consistent watering because their large, fast-expanding fruit is most vulnerable to BER.
Yes. Greenhouse plants have a longer season, higher temperatures and greater nutrient demand. Feed at the upper end of the range at the shorter frequency (every 2 weeks during peak). Outdoor plants generally need the mid-range at standard frequency (every 3–4 weeks). See the Growing Guide tab for detailed guidance.
British Biochar creates permanent porous habitat for beneficial microorganisms and increases K retention by 18–35%. Worm castings introduce living biology — a single gram contains hundreds of millions of organisms. Together they improve flavour and Brix even at identical NPK levels because it is the microbial community, not just the nutrients, that drives quality.
Yes. All plant-based organic ingredients with no synthetic chemicals and no persistent toxins. No withholding period for edible crops. Safe for pets and children once applied and watered in.
The product is made from organic and natural ingredients — plant meals, mined minerals, seaweed, biochar and worm castings. It is not certified organic. No synthetic chemicals, no GMO inputs.
Cool, dry place out of direct sunlight. Keep sealed between uses — exposure to moisture activates microbial populations prematurely. Effective for at least 18 months. If clumped, break up before measuring — still useable.
Often bought with this
20% of buyers here also chose Fruit & Vegetable Fertiliser
Fertiliser
Chilli & Pepper Fertiliser | Organic Feed
A balanced slow-release feed for chillies and peppers.
from £11.50
Fertiliser
Strawberry Fertiliser | Organic High Potash Plant Food
A high-potash slow-release feed for strawberries.
from £11.50
