Fertiliser
All Purpose Fertiliser 4-4-4
True all-purpose 4-4-4 for veg, fruit, flowers and containers.
from £12.00
Customer highlight
I’ve been using this product for two years now. Not only are my tomatoes thriving, but my potted houseplants have also perked up.
Editorial highlight from marketplace and store reviews — separate from the full review list below.
Humic Acid Granules: 70% humic acid, 100% water soluble, from premium leonardite
Humic Acid Granules are a fully water-soluble, 70% humic acid extract of premium leonardite in 1 to 3 mm granules. Humic acid is not a feed: it changes the soil your feed works in. It raises the soil's capacity to hold nutrients, feeds bacteria and fungi around the roots, and has auxin-like activity that drives root growth within days. The gains build season on season.
- Holds nutrients in the root zone. Raises cation exchange capacity, so minerals are held and released to roots instead of leaching away.
- More root, faster. Auxin-like activity drives root growth, with visible improvement in transplants within two weeks.
- Livelier soil. Stimulates bacterial and fungal biomass around the roots.
- Fully soluble. No residue to block sprayers or drip lines, unlike 80–90% "soluble" humates.
- Works with any feed. Makes organic and mineral fertilisers go further.
70% humic acid
100% water soluble
CEC 450 meq/100 g
1–3 mm granules
Drip-line grade
Vegan
Part of our humic and fulvic acid range. For the difference between the two, read humic vs fulvic acid.
What's in Humic Acid Granules
Leonardite humic acid (70%)
A refined, fully soluble extract of oxidised ancient lignite, the richest natural source of humic substances.
How to use Humic Acid Granules: foliar, drench, seed soak and compost tea rates
Working with the granules
Weigh the granules against the rate in the relevant card below, add to the volume of water required, and stir. They dissolve completely with stirring, a little faster in warm water. There is no sediment, no settling step, and no residue to manage. The solution will be very dark but completely clear. Apply on the same day you mix it. Extended storage allows microbial activity to develop in the bucket.
Staining warning
The solution stains porous surfaces: paving, concrete, grout, light-coloured clothing, and timber. Work over soil or grass. Rinse spills on hard surfaces immediately.
Foliar spray
Foliar application delivers humic acid directly to leaf tissue, where the auxin-like response is fastest. Yildirim (2007) found 20 ml/L of commercial liquid humate sprayed at 10-day intervals optimum for tomato, with Karakurt et al. (2009) confirming the same window for pepper. Eshghi and Garazhian (2015) identified 600–900 mg/L (active humic acid) as the strawberry sweet spot, with declining returns above 1000 mg/L. Commercial protocols summarised by Alsultana suggest 0.1–0.3% active concentration depending on crop sensitivity. Concentrations expressed below are for 70% humic acid granules.
Tomato, pepper, aubergine, cucurbits
Spray both leaf surfaces to runoff in early morning or late evening. Yildirim (2007) recorded the highest yield, fruit weight, and ascorbic acid content at this concentration window across two seasons of greenhouse tomato trials, with sprays at 10-day intervals from three weeks after planting.
Strawberries and soft fruit
Eshghi and Garazhian (2015) identified 600 mg/L as the lower bound and 900 mg/L as the upper bound of the optimum foliar window for strawberry. Both produced the highest dry shoot and root mass, with significant improvements in fruit ascorbic acid and total soluble solids over control.
Leafy vegetables and salad crops
Leafy crops respond at gentler concentrations and benefit from more frequent, lighter applications. Stay at the lower end of the rate range. Higher concentrations risk leaf marking on thin-leaved crops.
Roses, ornamentals and shrubs
Foliar application supports flower colour and stem vigour, particularly on roses growing in alkaline soils where iron uptake is restricted. For stressed plants, combine with the soil drench programme below.
Cereals, field crops and lawns
The Ma et al. (2024) meta-analysis of humic acid across cereal trials confirms the strongest response at 100–200 kg N/ha programmes, with cash crops and upland cereals out-responding paddy rice. For lawns, deliver via knapsack sprayer at standard turf coverage rates.
Soil drench
Drench delivers humic acid into the active root zone where it builds CEC, stimulates microbial biomass, and provides the auxin-like signal that drives lateral root development. Eshghi and Garazhian (2015) optimised strawberry drenches at 300–450 mg/L active humic acid every 14 days. The literature consensus is for monthly application at moderate strength, stepped up to 14-day intervals on stressed plants or alkaline soils.
General vegetable garden and allotment
Apply to moist soil around the root zone. Skip applications when soil is dry or plants are heat-stressed. Wait for the soil to be moist first.
Strawberries, soft fruit, fruiting containers
This matches the Eshghi and Garazhian (2015) optimal soil treatment for cultivar Paros strawberry: significant gains in fruit number, total yield, and ascorbic acid against control. The 14-day interval was the trial schedule.
Roses and ornamentals on alkaline or stressed soils
Shaygan (2024) demonstrated that 1000 mg/L drenches every 15 days for two months on rose under alkaline stress lifted total protein, proline, and antioxidant activity above control, with sugar content peaking at 500 mg/L. The higher rate is the stress-management option. Drop back to 500 mg/L (0.7 g granules per litre) once vigour returns.
Transplant drench
Apply directly into the planting hole before setting the root ball. Auxin-like root stimulation typically appears within 48–72 hours, with significant reductions in transplant shock and faster establishment recorded in the Canellas et al. (2015) review.
Container and peat-free compost conditioning
Peat-free media is naturally low in humic substances. Regular drenches replenish humic content, raise CEC of the growing medium so it holds nutrients more like a peat-based mix, and extend compost working life. Particularly valuable in season-long container crops.
Seed soak (pre-sowing treatment)
Pre-sowing seed treatment with humic acid is one of the best-evidenced uses of the material. Kadhim and Hamza (2021) recommend maize seeds soaked at 1 ml/L of commercial humate for 18 hours before spring sowing: significant gains in emergence percentage, seedling root length, and seedling vigour. Killi (2004) confirmed 16-hour soak as optimal for cotton in potassium humate solution. Across cereals, legumes, and vegetables, the literature points to dilute concentrations and longer soak times rather than concentrated short dips.
Tomato, pepper, aubergine, cucurbits
Soak seeds at room temperature in a shallow dish. Sow immediately afterwards. Do not redry. Faster germination and stronger first true leaves are the typical response.
Cereals, maize and wheat
This matches the Kadhim and Hamza (2021) protocol for spring maize on cultivars Baghdad3, 5018 and Sumer. Drain seeds briefly before sowing. Do not redry. The longer soak time reflects cereal seed coat permeability.
Beans, peas and other legumes
Azhar (2026) evaluated faba bean (cultivar Barcino) seed treatments at 100–300 mg/L active humic acid, with response peaking in the middle of that range for germination index and seedling vigour. Do not exceed 12 hours: legume seeds split with prolonged soaking.
Salad and leafy greens
Small seeds need the lightest treatment. A 2–4 hour soak in the dilute solution lifts germination uniformity without risk of inhibition.
Flowers and ornamentals
Hartwigsen and Evans (2000) demonstrated significant root development gains in marigold and geranium from pre-sowing humate seed soak. Adjust soak time to seed size: small seeds 4 hours, larger seeds up to 12.
Compost tea
Humic acid added during compost tea brewing serves two purposes: it binds chlorine and chloramine in mains water (protecting the microbial population in the tea), and it acts as a food source that documented research shows stimulates fungal biomass during the brew. Crophealth research used 30 ml of liquid humic extract per 15 L of standard recipe, broadly equivalent to a few grams of these granules scaled to brew volume.
Standard 20 L aerated compost tea brew
Dissolve the granules into the water first and let the brewer run for 5–10 minutes. This binds chlorine in mains water before the microbial inoculant arrives. Then add compost, kelp, fish hydrolysate, or whichever other ingredients your recipe uses. Brew at 18–24°C for 18–24 hours and apply within 4 hours of switching off the air pump.
Small batch (5 L watering can brew)
For aerated bucket-scale brews or steeped (non-aerated) compost extracts. Same protocol: dissolve, wait briefly, then add compost.
Fertigation and combined liquid feed
Fertigation and drip irrigation
Add the dissolved granules to the reservoir after the main nutrient solution is mixed. Compatible with all liquid nutrient programmes. Because the granules are fully soluble, emitters will not clog at these rates.
Combined with liquid feed
Humic acid enhances uptake efficiency of every mineral in the feed. Always add the dissolved granules to the already-diluted feed, not to undiluted concentrate, to avoid precipitation.
Works well combined with
Pair with Fulvic Acid Powder in every liquid feed for complete humic-plus-fulvic coverage: humic works in the soil, fulvic works inside the plant. Stack with Seaweed Powder for biostimulant compounding: seaweed delivers cytokinins and auxins, humic improves uptake and soil biology. Fully compatible with all Dr Forest crop-specific fertilisers as a general efficiency booster.
How Humic Acid Granules work
Humic substances are large, carbon-rich molecules dominated by carboxyl and hydroxyl groups. Those groups do the work.
- Cation exchange. Their negative charge holds calcium, magnesium and potassium against leaching.
- Chelation. They bind micronutrients into plant-available forms and help release phosphorus.
- Root growth. Humic substances stimulate root growth and nutrient uptake (Nardi et al., 2002; Canellas & Olivares, 2014).
More is not better: the response curve is bell-shaped. For strawberry, Eshghi and Garazhian (2015) found the best results at 600–900 mg/L as a foliar spray and 300–450 mg/L as a drench.
References
- Eshghi, S. & Garazhian, M. (2015). Improving growth, yield and fruit quality of strawberry by foliar and soil drench applications of humic acid. Iran Agricultural Research, 34(1), 14–20.
- Nardi, S., Pizzeghello, D., Muscolo, A. & Vianello, A. (2002). Physiological effects of humic substances on higher plants. Soil Biology & Biochemistry, 34, 1527-1536.
- Canellas, L. & Olivares, F. (2014). Physiological responses to humic substances as plant growth promoter. Chemical and Biological Technologies in Agriculture, 1, 3.
Figures from published research are not a trial of this product.
Use Humic Acid Granules with
- Fulvic Acid Powder for Plants: humic works in the soil, fulvic works inside the plant.
- Liquid Seaweed Brix+: a monthly drench partner for roots and soil biology.
- Boron Humate Granules: boron on a humic carrier for brassicas, fruit set and roots.
Which to choose: these granules dissolve for drenches and sprays. Slow Release Humic Acid is the insoluble granule you spread on lawns and beds to release over months. The Humic and Fulvic Acid Pair gives you both fractions.
Humic Acid Granules FAQs
No. It is a soil conditioner and nutrient efficiency enhancer, not a primary nutrient source. Keep feeding as normal.
If you start one programme, make it a monthly soil drench. It builds exchange capacity and microbial biomass in the root zone, where most of the work happens.
Transplants and seed-soaked crops show root improvements within two weeks. In established plants the gains build over the season.
No. The response is bell-shaped, so extra humic acid can cut the benefit.
Yes. Leonardite humic acid has no known toxicity to mammals, birds, bees or soil invertebrates at realistic rates.
Use it the same day. In water it becomes food for microbes in the bucket.
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