Dr Forest
Chilli & Pepper Fertiliser | Slow Release Natural Plant Food | High Flavour & Heat | UK
Chilli & Pepper Fertiliser | Slow Release Natural Plant Food | High Flavour & Heat | UK
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Chilli & Pepper Fertiliser 3-3.5-7 — designed for heat, flavour and aroma
Most chilli fertilisers push yield. This one is designed around heat and flavour. The 3-3.5-7 NPK ratio — with potassium at more than twice the nitrogen level and phosphorus above nitrogen — drives capsaicin biosynthesis, volatile production and sugar accumulation in developing fruit. Twenty ingredients including Yorkshire Polyhalite, Phosphorous Meal, Gypsum, Alfalfa Meal and EM-1 Microorganisms deliver a complete slow-release feed with 7% calcium to prevent blossom end rot and 6.4% sulphur from four sources for volatile flavour compound production. Handcrafted in Stockport — no slaughterhouse waste.
Nitrogen is deliberately moderate at 3% — sufficient for healthy canopy without the excess that dilutes capsaicin concentration, suppresses volatile production and produces large, mild fruit. Phosphorus at 3.5% — drives ascorbic acid (vitamin C) production and sugar accumulation — the sweetness and tang that define a properly grown pepper.
What this formula does for your chillies and peppers
- Hotter chillies — moderate nitrogen preserves capsaicin concentration; excess N is the single most common cause of disappointingly mild superhots in home growing
- Sweeter, more complex flavour — phosphorus drives ascorbic acid and sugar accumulation; chloride-free potassium drives phloem loading of sugars into developing fruit
- Richer aroma volatiles — 6.4% sulphur from Yorkshire Polyhalite, SOP, Gypsum and Epsom Salt supports the biosynthesis of esters, aldehydes and terpenoids that define pepper aroma
- No blossom end rot — 7% calcium from four sources provides continuous supply that prevents cell wall failure in rapidly expanding fruit
- Living soil biology — EM-1 Microorganisms and chitin from Mealworm Frass build the competitive microbial community that suppresses Phytophthora and produces secondary metabolites linked to improved flavour
- Trace mineral depth — Scottish Seaweed, Volcanic Rock Dust and Clay Minerals supply the enzyme cofactors for capsaicinoid and volatile biosynthesis
Dr Forest Chilli vs general tomato feed
Dr Forest Chilli & Pepper 3-3.5-7
- 20 ingredients — 7% Ca, 6.4% S, 2.3% Mg and broad trace minerals
- Phosphorus for ascorbic acid and sugar accumulation
- Moderate N preserves capsaicin concentration in hot varieties
- 6.4% sulphur from four sources for volatile compound production
- Magnesium from three sources — cofactor in capsaicin enzymatic pathway
- Apply every 2–4 weeks — not weekly
General Tomato Feed Used for Chillies
- Designed for yield, not heat or flavour complexity
- No calcium — the nutrient that prevents blossom end rot
- No sulphur — the element that drives volatile production
- Often high-N — actively suppresses capsaicin biosynthesis
- No soil biology — soluble salts suppress beneficial organisms
- Weekly dosing with feast-and-famine nutrient cycle
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 slaughterhouse waste. No shortcuts.
All 20 ingredients — what they do and why they are in the formula
Every ingredient is here for a specific, research-backed reason. Nothing is filler. This formula has been optimised for capsaicin biosynthesis and volatile flavour compound production — the chemistry that makes chillies hot and peppers flavourful.
Nitrogen Plant Extract — Plant-derived, controlled release
The primary nitrogen carrier at 12% N, making up 20% of the blend. Mineralises over 6–8 weeks without nitrate spikes. For chillies, controlled nitrogen is critical — excess N redirects the plant's phenylalanine pool away from capsaicin synthesis and toward protein production, directly reducing heat.
Yorkshire Polyhalite — North Yorkshire, slow release 50–60 days
K, Ca, Mg and S from a single crystal at 16.5% of the blend. The sulphur fraction is particularly important for chillies — it drives volatile biosynthesis through the sulphur-containing amino acid methionine, a precursor to many pepper aroma compounds. Extends K supply for 50–60 days.
Phosphorous Meal — Plant-derived, fast-moderate release
At 15% P and 9% Ca, making up 15% of the blend — the largest P source. Elevated phosphorus drives ascorbic acid (vitamin C) biosynthesis and sugar accumulation. Also supports root development and flower initiation — chillies set fruit on every node, so continuous flowering support is critical.
Gypsum (Calcium Sulphate) — Mineral, immediate release
23% calcium and 18% sulphur in immediately plant-available sulphate form. The largest single calcium source at 9% of the blend. Prevents blossom end rot. The sulphur fraction supports volatile compound production. Delivers Ca without raising soil pH.
Sulphate of Potash (SOP) — Mineral, immediate release
Fast-acting potassium at 50% K₂O — chloride-free. Activates sugar transport, carotenoid production and volatile biosynthesis immediately. The sulphur anion (18% S) contributes directly to the four-source sulphur profile that distinguishes this formula.
Alfalfa Meal — Plant-based, slow release, biostimulant
Contains triacontanol — a natural growth regulator that increases chlorophyll content by 15–20%. Also supplies amino acid precursors for capsaicinoid synthesis. The phenylalanine in decomposing Alfalfa feeds the PAL pathway — the biosynthetic route to capsaicin.
Epsom Salt (Magnesium Sulphate) — Mineral, immediate release
17.7% Mg and 14% S in immediately plant-available form. Magnesium is a cofactor in the capsaicin enzymatic pathway — Mg-deficient chilli plants produce measurably less capsaicin. The fastest-acting Mg source, addressing deficiency within days.
Scottish Seaweed Meal — Hand-harvested
Over 60 trace elements. Natural cytokinins delay leaf and fruit senescence — extending the productive season. Particularly valuable for chillies which fruit over a long period from midsummer through to first frost.
Magnesium Carbonate — Mineral, moderate release
20.7% Mg. A secondary magnesium source bridging the gap between Epsom Salt's immediate availability and Yorkshire Polyhalite's sustained release. Three Mg sources maintain uninterrupted chlorophyll production and capsaicin enzyme activity throughout the season.
Micronised Rock Phosphate — Mineral, slow reserve
31% P and 46% Ca. Dissolves slowly as a long-term P and Ca reserve. Handles late-season demand when chillies are still setting and ripening fruit on every node from August through October.
Humic Acid & Fulvic Acid — Mineral organic, chelation
Chelates micronutrients, increases soil bacterial biomass by 30–60%, stimulates mycorrhizal colonisation by 25–40%. Research shows 15–30% higher Brix and elevated phenolic compounds in humic acid-treated pepper trials.
Fermented Biochar — British, activated
Permanent porous carbon scaffold. Increases K retention by 18–35% under leaching conditions — particularly valuable in containers and grow bags where chillies are most commonly grown in the UK.
Rapeseed Meal — British, slow release
Steady nitrogen over 6–8 weeks through microbial breakdown. Acts as a prebiotic carbon source. The gradual mineralisation avoids the nitrate spikes that suppress capsaicin biosynthesis and dilute fruit quality.
Mealworm Frass — Sustainably reared, SAR activator
Contains chitin. Plants detect it as a pest signal and upregulate Systemic Acquired Resistance, priming defences against Phytophthora, Botrytis and bacterial spot — the most common pepper diseases in UK growing.
Clay Minerals — British, permanent CEC reservoir
Montmorillonite and illite clays. Ionic reservoirs that bind and slowly release K, Ca and Mg between waterings. Valuable in the container mixes where chillies are most commonly grown.
Seaweed Extracts — British coastal, biostimulant
Concentrated cytokinins, betaines and mannitol. Enhances nutrient uptake, flower set and fruit development under stress. Chillies are particularly responsive to seaweed biostimulants during the transition from vegetative growth to fruiting.
Volcanic Rock Dust (Basalt) — Mineral, trace elements
Zinc, iron, copper, manganese — the enzyme cofactors for capsaicinoid biosynthesis and volatile aroma compound production. These trace minerals are catalysts in the pathways that produce the specific heat and flavour profile of each variety.
EM-1 Microorganisms — Living culture
Bacteria, yeasts, actinomycetes and lactic acid bacteria. Suppresses pathogens through competitive exclusion. Produces bioactive compounds that enhance secondary metabolite production — the capsaicinoids and flavour volatiles in developing fruit.
Silica Meal — Mineral, structural
Silicon strengthens cell walls — a physical barrier against aphid stylet penetration and fungal spore germination. Improves stem rigidity, reducing collapse under heavy fruit load. Chillies loaded with ripe fruit on every node need structural support.
Herbal Mixture — Plant-derived, biostimulant
Comfrey (K-rich, rapid breakdown), nettle (iron, silica), yarrow (phosphorus-solubilising bacteria), chamomile (rhizobacteria support). Broad-spectrum biological stimulus.
How to use chilli & pepper fertiliser: rates, timing & method
Start feeding 10–14 days after transplanting once plants show new growth. Apply every 2–3 weeks during active growth, then stretch to every 3–4 weeks as fruit matures to concentrate capsaicin, sugars and volatiles. Superhots often prefer lighter feeding for maximum heat — observe your plants and adjust.
Soil preparation — before planting or at transplanting
Beds and raised beds
100g/m² for fertile soil or mild varieties. 150g/m² for average garden soil — standard feeding for good heat and flavour. 200g/m² for maximum heat, aroma and volatile production — this rate delivers a strong potassium and sulphur foundation for the season.
Single plants at transplanting
Leave a 10cm gap between the stem and the fertiliser ring. 18–20g for small transplants or superhots. 25–30g for standard varieties. 35–40g for large established plants or when pushing maximum flavour in sweet peppers.
Containers and pots
5g/L if using mycorrhizal fungi inoculant (lower P avoids suppressing colonisation). 10g/L in plain compost. Most UK chilli growers grow in containers — this initial charge is the foundation.
Top-dressing — feeding through the season
Rows and beds
100g/m for superhots and early-season maintenance. 120g/m for standard feeding. 160g/m during peak fruiting for maximum volatile and capsaicinoid production. Spread in a narrow band 10–15cm from stems. Scratch in lightly. Water well. Feed every 2–3 weeks during active vegetative growth, stretch to every 3–4 weeks once fruit is setting and ripening — reducing frequency as fruit matures concentrates heat and aroma.
Single plants — in-ground or raised beds
15–20g for superhots and ornamentals — light feeding preserves capsaicin concentration. 25–30g for standard hot and mild varieties. 35–40g for sweet peppers and when pushing maximum flavour and aroma. Sprinkle in a ring 10–15cm from stem. Incorporate lightly. Water in.
Containers and pots
1g/L for mild varieties and early-season maintenance. 2g/L for standard feeding. 3g/L during peak fruiting for maximum heat, flavour and aroma — this rate pushes potassium delivery into the peak capsaicin and volatile production zone.
3 level teaspoons = 1 tablespoon ≈ 15g. Mix the fertiliser with an equal volume of compost before application — reduces dust, coats the granules in microbe-rich compost, and supports the living biology for enhanced capsaicin and aroma compounds.
Stop or reduce feeding in the last 4–6 weeks before final harvest if plants are performing well. Ease off watering slightly when fruit is ripening — mild water stress concentrates capsaicin, sugars and volatiles for hotter, bolder peppers without cracking or splitting.
Use Dr Forest Seaweed Powder as a fortnightly foliar — boosts volatile production and stress tolerance. Apply Dr Forest Liquid Gypsum every 2–4 weeks for additional calcium. Apply mycorrhizal fungi at planting for improved nutrient uptake — research shows yield increases of 20–50% in inoculated peppers.
Cool, dry place out of direct sunlight. Keep sealed between uses. Effective for at least 18 months.
Chilli & pepper growing guide — varieties, training & feeding by type
Different pepper types have fundamentally different nutritional needs. A sweet bell pepper and a Carolina Reaper are both Capsicum, but their feeding programmes should differ substantially.
Feeding adjustments by variety type
Sweet peppers — Bell, Ramiro, Marconi, Jimmy Nardello, Padron
Sweet peppers benefit from full-strength feeding. The phosphorus drives ascorbic acid (vitamin C) and sugar accumulation — the sweetness and tang that define a good sweet pepper. Use the upper rate range and maintain frequency throughout fruiting. These varieties have zero capsaicin — flavour is entirely about sugars, acids and aromatic volatiles.
Mild–medium chillies — Jalapeño, Poblano, Anaheim, Hungarian Wax, Serrano
The varieties where you want both heat and complex flavour. Standard rates, standard timing. These respond well to the K-led 3-3.5-7 formula — potassium drives sugar loading while moderate N preserves the capsaicin that gives these varieties their character.
Hot chillies — Scotch Bonnet, Habanero, Birds Eye, Cayenne, Thai
The Capsicum chinense varieties (Scotch Bonnet, Habanero) have the most complex aroma profiles of any peppers — fruity, floral, tropical esters alongside serious heat. Lighter feeding preserves capsaicin concentration. Overfeed and you dilute the heat with water and vegetative growth.
Superhots — Carolina Reaper, Trinidad Scorpion, Bhut Jolokia, Komodo Dragon
Superhots are the varieties where moderate nitrogen makes the biggest difference. Excess N is the single most common cause of disappointing SHU in home-grown superhots. Feed lightly, water consistently, and allow mild stress during ripening. The capsaicin concentration that makes a Reaper a Reaper is produced under nutritional constraint, not abundance.
Ornamental peppers — Prairie Fire, Black Pearl, Medusa, Numex Twilight
Minimal feeding. The K and S from Polyhalite drive anthocyanin production for the vivid purples, reds and oranges these varieties display. Excess N produces leggy growth and dilutes colour intensity.
Greenhouse vs outdoor
Greenhouse, polytunnel & windowsill
- Essential for superhots and most hot varieties in the UK climate
- Longer season — plant out April, harvest through to October
- Higher temperatures accelerate capsaicin biosynthesis
- Feed at the upper end, every 2–3 weeks during peak
- Ventilate well — stagnant air promotes Botrytis
- Water in the morning to allow foliage to dry
Outdoor growing
- Realistic only for mild–medium varieties in most of the UK
- Shorter season — transplant after last frost (late May), harvest July–September
- Choose early-maturing varieties: Jalapeño, Padron, Cayenne, Hungarian Wax
- Feed at mid-range, every 3–4 weeks
- Shelter from wind — peppers are easily damaged
- Fleece overnight if temperatures drop below 10°C
UK seasonal timeline
| Month | What to Do |
|---|---|
| Jan–Feb | Sow superhots and slow varieties indoors at 25–30°C. Use a heated propagator. Superhots need 10–14 days to germinate. |
| March | Sow mild–medium varieties indoors at 20–25°C. Pot on superhots to 9cm pots. Begin feeding seedlings at quarter strength once they have 4 true leaves. |
| April | Pot on to final containers. Prepare greenhouse beds with base dressing (100–200g/m²). Transplant to greenhouse positions. Begin full feeding programme 10–14 days after transplanting. |
| May | Transplant outdoor varieties after last frost (late May). First flowers on greenhouse plants. Feed every 2–3 weeks. Pinch out growing tip at 30cm for bushier plants (optional for most varieties). |
| June–July | Peak feeding period. Fruit setting on all nodes. Feed every 2–3 weeks at upper end. Support plants with canes or cages as fruit load increases. Remove any fruit touching the soil. |
| August | First ripe fruit on most varieties. Begin stretching feed interval to 3–4 weeks. Reduce watering slightly to concentrate capsaicin and sugars. Harvest regularly to encourage continued fruiting. |
| Sep–Oct | Main harvest. Stop feeding 4–6 weeks before final harvest. Green fruit ripens on the plant or on a sunny windowsill after picking. Pull plants before first frost. |
Common problems
Blossom end rot
The 7% calcium in this formula provides the mineral — but calcium reaches fruit only via the transpiration stream. Consistent, deep watering is as important as calcium supply. Dr Forest Liquid Gypsum as a root drench helps in severe cases. Remove affected fruit.
Flower drop
Maintain consistent temperatures. Water regularly. If feeding at the upper end, reduce rate. The moderate 3% N in the formula minimises N-related flower drop, but very fertile soil plus high feeding rates can still trigger it.
Aphids
Silica Meal in the formula strengthens cell walls, reducing stylet penetration. Biological controls: ladybirds, lacewing larvae, parasitic wasps. Neem oil spray as a last resort. Strong, well-fed plants resist aphid colonisation better than stressed ones.
Disappointing heat levels
Reduce feeding frequency. Allow mild water stress during ripening. Ensure 6+ hours of direct sun. Capsaicin is produced as a stress response — comfortable plants produce less of it. Superhots need sustained temperatures above 25°C for maximum SHU.
Sunscald
Maintain adequate foliage canopy to shade fruit. Do not over-defoliate. In greenhouses, shade netting during heatwaves. Affected fruit is edible but has reduced shelf life.
The science of chilli heat, pepper flavour and why nutrition is decisive
Pepper flavour combines four systems: capsaicinoids (heat — capsaicin and dihydrocapsaicin account for 90% of perceived pungency), sugars (fructose and glucose for sweetness), organic acids (ascorbic acid for tang and vitamin C), and volatile organic compounds (179–208 identified VOCs including esters, aldehydes and terpenoids). All four are profoundly influenced by nutrition.
The capsaicin-nitrogen connection
Capsaicin is synthesised from phenylalanine via the phenylpropanoid (PAL) pathway. The same phenylalanine pool is also used for protein synthesis. When nitrogen is abundant, the plant preferentially directs phenylalanine toward protein for new growth. When N is moderate, more phenylalanine is available for the PAL pathway — producing more capsaicin, more phenolic compounds, and more lignin for structural strength. This is why high-nitrogen chillies are often disappointingly mild.
Why phosphorus matters for peppers
Phosphorus drives two quality metrics specific to peppers: ascorbic acid (vitamin C) biosynthesis and sugar accumulation. The P-ascorbic acid link is well-documented in Capsicum trials — P-deficient peppers have measurably lower vitamin C and sugars. At 3.5% P, the formula supports continuous ascorbic acid production throughout the fruiting season.
Mechanisms of action
Capsaicin preservation through moderate nitrogen
Moderate N preserves the phenylalanine pool for the PAL pathway. Organic N mineralises slowly, providing a steady trickle rather than the nitrate spike that diverts phenylalanine to protein production.
Potassium drives sugar transport and volatile production
K activates sucrose synthase and drives phloem loading into developing fruit. Higher Brix, higher fructose, and increased substrate for ester and aldehyde biosynthesis.
Sulphur and volatile aroma compounds
6.4% sulphur from four sources (Polyhalite, SOP, Gypsum, Epsom Salt). Sulphur-containing amino acids are precursors to many key pepper volatiles. Sulphur also drives carotenoid accumulation — the pigments responsible for red, orange and yellow fruit colour.
Magnesium as capsaicin enzyme cofactor
Magnesium is a cofactor in the enzymatic pathway that converts vanillylamine and fatty acyl-CoA into capsaicin. Mg-deficient plants produce measurably less capsaicin. Three Mg sources at different speeds maintain uninterrupted enzyme activity.
Calcium for fruit quality and shelf life
7% calcium from four sources strengthens pectin cross-links in cell walls. Firmer fruit that resists bruising and deterioration. Continuous Ca supply prevents blossom end rot — particularly important in long-season container chillies.
Microbial metabolites and flavour complexity
Decomposing organic ingredients generate secondary metabolites that enter the plant and directly influence volatile biosynthesis. Organic management consistently produces peppers with higher total VOC content (179–208 compounds identified).
Study data
| Study | Finding |
|---|---|
| Organic trials incl. Topepo variety (2020–2024) | Organic: total phenols, flavonoids, ascorbic acid, carotenoids, sugars and 179–208 aroma volatiles enhanced 15–50% vs controls. |
| AMF/biofertiliser combination trials (2023–2024) | Organic + biological: higher yield, phenols, lycopene, β-carotene, antioxidant activity. Organic outperformed chemical for nutritional and flavour quality. |
| Global meta-analysis (2023), 7,859 data pairs | NPK + organic: nutritional quality +12% average. Peppers identified as highly responsive. Higher relative P and K support sugars, vitamin C and flavour. |
References
- Marschner, P. ed. (2012). Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press.
- Wang, Y. et al. (2023). Combined organic–mineral fertilisation meta-analysis. Science of the Total Environment.
- Materska, M. & Perucka, I. (2005). Antioxidant activity of capsaicinoids. J. Agric. Food Chem.
- Nardi, S. et al. (2009). Physiological effects of humic substances. Soil Biology and Biochemistry.
- Khan, A.A. et al. (2009). Triacontanol. Plant Growth Regulation, 53(3), 203–218.
- Craigie, J.S. (2011). Seaweed extract stimuli. J. Applied Phycology, 23(3), 371–393.
- Lehmann, J. et al. (2011). Biochar effects on soil biota. Soil Biology and Biochemistry, 43(9), 1812–1836.
- Johnston, A.E. & Dawson, C.J. (2018). Polyhalite as a fertiliser. Proc. 826, Int. Fertiliser Society.
Frequently asked questions
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