Foliar feeding is where most growers judge a humic product, because leaves respond fast and they respond honestly. A potassium humate solution that is properly filtered, correctly dosed and sprayed at the right hour can visibly lift leaf colour, fruit set and recovery from heat stress within days. Sprayed carelessly — too concentrated, mixed with the wrong tank partner or applied at midday — the same material can burn young tissue and waste a whole season of budget. Based on the material we ship daily from our Shizuishan plant and the feedback we collect from distributors and agronomists in more than thirty markets, this guide walks through how to use potassium humate as a foliar input in a repeatable, low-risk way.
Why Foliar Potassium Humate Works Differently From Soil Application
Soil-applied potassium humate mainly rebuilds the growing medium: it improves aggregate stability, raises cation exchange capacity and feeds microbial activity over weeks. A foliar spray works on the leaf itself. Humic and fulvic fractions in the solution act as carriers at the cuticle, helping potassium, micronutrients and some agrochemicals cross into leaf tissue more evenly, while the potassium fraction supports stomatal regulation and enzyme activation. In trial plots we have supplied to vegetable growers in Southeast Asia and Turkey, three foliar passes of a 0.15%–0.25% potassium humate solution during flowering and early fruit enlargement typically produced darker, thicker leaves and a 6%–12% increase in marketable fruit weight against untreated checks. Numbers vary with cultivar and climate, but the direction of the response is consistent enough that foliar use is now the default recommendation for high-value horticultural crops.
- Fast visible response: leaf colour and turgor usually improve within 3–7 days.
- Low unit cost per hectare: 150–300 g of water-soluble granular potassium humate per hectare per pass.
- Complements rather than replaces nutrition — it improves the efficiency of what is already in the tank.
- Useful at stress moments: heat, cold snaps, transplant shock, hail recovery, heavy fruit load.
Choosing Material That Is Actually Safe to Spray
Not every potassium humate belongs in a sprayer. Material ground from crude ore for soil use carries insoluble matter that will blind fine nozzles and scratch the inside of your leaf. For foliar work we specify our water-soluble grades — 60 mesh or 80 mesh granular, or micronized flakes — and we hold them to the following profile before they leave the factory:
- Humic acid (dry basis): 55%–60% minimum, typically 58% on our soluble export grades.
- Potassium (K2O): 10%–12%, which is what makes it potassium humate rather than sodium humate.
- pH of a 1% solution: 9–11, fully dispersed with no sediment.
- Insoluble residue (acid insolubles plus sand): low enough to pass a 200-mesh screen test — we run this on every lot.
- Heavy metals and sodium: batch-tested to keep Na below the limit that causes leaf-tip burn on sensitive crops.
- Moisture: kept under 15% so granules dissolve in under a minute in the mixing tank.
A practical field test before you buy a container: dissolve 10 g in one litre of clean water, stir for sixty seconds, let it stand for ten minutes and pour it through a white coffee filter. A good foliar-grade potassium humate leaves a light tan residue at most, and the filtrate stays a clear dark brown. Grit at the bottom of the funnel is your answer, whatever the certificate claims.
Tank Mix Order and Compatible Partners
Potassium humate is mildly alkaline and chemically active, so how you build the tank matters as much as how much you use. Our technical team hears more complaints about tank-mix sequence than about the product itself. Follow this order and jar-test every new combination:
- Fill the spray tank two-thirds with water and start the agitator.
- Add potassium humate granules first, circulating for 5–10 minutes until fully dissolved.
- Add dry fertilisers and soluble salts (urea, MAP, mono-potassium phosphate, magnesium sulphate).
- Add chelated micronutrients; humate helps keep iron, zinc and manganese available in solution.
- Add wettable-powder crop protection products, then suspensions, then oils.
- Adjust pH to 5.5–6.5 for tank mixes with pesticides, then top up to volume.
Do not combine potassium humate with strongly acidic products, calcium nitrate at high concentration, or oil emulsions applied to young, waxy foliage without testing. Avoid mixing with any pesticide whose label states a pH ceiling below 5.0. Always run a one-litre jar test for fifteen minutes and look for floc, curdling or heat before filling a 1,000-litre tank.
Rates by Crop and Growth Stage
These are the rates we recommend on our water-soluble 60-mesh granular potassium humate, expressed per hectare with typical boom-spray volumes of 400–800 L for field crops and 800–1,200 L for established orchards.
- Vegetables under protected cultivation (tomato, pepper, cucumber, strawberry): 1.0–2.0 kg/ha, first pass at first truss flowering, then every 10–14 days.
- Leafy greens and herbs: 0.8–1.2 kg/ha at 4–6 leaf stage; keep strength low to avoid tip scorch on tender tissue.
- Tree fruit (apple, pear, peach, citric, table grape): 2.0–3.0 kg/ha at petal fall, 3.0 kg/ha at fruit enlargement, 2.0 kg/ha before colour change.
- Field crops (maize, wheat, rice): 0.6–1.0 kg/ha, ideally combined with a late urea or phosphate pass. Maize at V6–V8 and wheat at tillering and early boot give the cleanest responses we see reported.
- Transplant recovery dips: 200–300 g per 100 L as a drench or tray wash before planting out.
Foliar potassium humate stacks with, rather than replaces, a soil programme. Growers who apply 8–12 kg/ha granular to the bed before planting and then run two or three foliar passes usually get a better return than those who rely on either route alone.
Spray Conditions That Decide the Result
- Timing: early morning after dew dries, or late afternoon. Stomatal uptake on our test plots was clearly poorer at midday, and heat evaporates the droplet before the humate can work.
- Droplet size: 200–400 microns, medium droplet, with fine-atomising nozzles only when humidity is above 60%.
- Coverage beats volume. Two lighter passes with good lower-leaf coverage outperform one heavy soak.
- Water quality: use clean water below 500 ppm chlorides where possible; salty bore water combined with high humate strength is the most common cause of marginal tip burn.
- Adjuvants: on waxy leaves (olive, onion, cabbage) add a non-ionic surfactant; our soluble grades usually need none on soft-leaved crops.
- Clean-out: flush the sprayer with clean water at the end of the day. Humate solutions left standing will deposit on filters and pump seals.
Tank Mix Recipes Our Customers Repeat Season After Season
These are three combinations we hear requested most often with re-orders, and they illustrate how potassium humate earns its place as a carrier and efficiency input:
- Tomato colouring mix: 2 kg/ha water-soluble potassium humate + 8 kg/ha mono-potassium phosphate + chelated boron and calcium (separate injection for calcium). Applied 14 days apart, this improves fruit firmness and even colour on vine-ripened fruit.
- Maize stress mix: 0.8 kg/ha potassium humate + 10 kg/ha urea (28% N solution basis) + 2 kg/ha magnesium sulphate at V6–V8, repeated at tasselling. It supports green leaf area retention during hot, dry spells.
- Post-stress rescue: 1.5 kg/ha potassium humate + amino acids + zinc, sprayed within 48 hours of hail, frost or herbicide shock, to rebuild leaf area on new growth.
Troubleshooting Foliar Applications
- Leaf-tip burn after the first pass: reduce rate by half, check water chloride, spray later in the day.
- Sediment in the tank: the material is a soil grade, not a foliar grade — request 80 mesh or micronized from your supplier and repeat the filter test.
- No visible response: usually the crop was already potassium- or nitrogen-sufficient; evaluate over two to three seasons and check soil potassium status first.
- Foaming: run the agitator lower and add a silicone anti-foam; foaming is physical, not a quality defect.
Frequently Asked Questions (FAQ)
1. Can potassium humate be used as a foliar spray, or is it only a soil amendment?
Both routes work, but only water-soluble grades belong in a sprayer. For foliar use choose 60 or 80 mesh granular, or micronized flakes, with humic acid above 55% and insoluble residue low enough to pass a filter test. Soil grades ground from crude ore will block nozzles and leave grit on the leaf. Foliar potassium humate gives a fast visible response on leaves and fruit, while soil application builds structure and microbial activity over the whole season. On high-value crops we recommend combining them rather than choosing between them.
2. How much potassium humate should I put in a foliar tank per hectare?
For protected vegetables use 1.0–2.0 kg per hectare per pass, tree fruit 2.0–3.0 kg, and field crops such as maize and wheat 0.6–1.0 kg in 400–800 L of water. Dissolve the granules into the partly filled tank with the agitator running before adding anything else. If you have never sprayed the product on that cultivar, start at half the recommended rate and confirm leaf tolerance after 48 hours before scaling up.
3. Is potassium humate safe to mix with fertilisers and pesticides in the same spray?
Yes with most solid fertilisers, chelated micronutrients and many pesticide formulations, provided you add the humate to water first, then the dry products, then wettable powders and oils, and keep tank pH between 5.5 and 6.5 when pesticides are involved. Avoid combining it with strongly acidic products, concentrated calcium nitrate, or any formulation whose label sets a pH below 5.0. A one-litre jar test over fifteen minutes takes almost no time and protects an entire tankload.
About Us
NANJING MAXFIELD CROP SCIENCE CO.,LTD. is a manufacturer and exporter specialising in potassium humate and related organic soil inputs. Our factory stands in Shizuishan, Ningxia, one of China's key production hubs for humic acid raw materials, which puts us close to the leonardite resource our product line begins with. We control every phase in-house — raw material selection and storage, milling, granulation, screening and packaging — using a modern automated production model that removes the variability of manual feeding and gives us consistent concentration and particle size from lot to lot, which is exactly what foliar applications demand.
For spray-tank users we supply water-soluble potassium humate granular in 60 mesh and 80 mesh, plus micronized flakes, typically at 55%–60% humic acid and 10%–12% K2O, with every lot backed by COA testing on pH, moisture, insoluble residue, heavy metals and a dissolution screen. We also produce plant-source and mineral-source fulvic acid, amino acids, seaweed extract and compound amino acid products that mix with humate in the tank. A dedicated international trade department in Jiangsu Province handles enquiries, documentation and after-sales technical support for our global partners. If you are sourcing potassium humate for foliar programmes, private label packing or large-volume soil use, contact us at info@maxfieldcorp.com and we will quote and, on request, send 60 mesh and 80 mesh samples for your own jar and filter tests.
