Humic Acid and Iron Chelate: How to Use Them Together

The Humic Iron Complex is 500 g of humic acid powder (potassium humate, 80%+ humic acid, 10% K₂O) and 500 g of iron chelate (6% iron as Fe-EDDHSA). Use it when new leaves come through yellow with green veins. Dissolve the humic acid first and the iron last, pour it onto moist soil, and water it in straight away.

80%+ Humic Acid6% Iron (Fe-EDDHSA)Works to pH 9Humic First, Iron LastWater It In

Our Humic Iron Complex pairs our Humic Acid Powder with our Iron Chelate. This guide shows you how to use humic acid and iron chelate together: when to reach for them, how much of each to mix for pots, beds, lawns and citrus, how to get both into one can safely, and a simple plan for the season.

The best time for a first dose is late winter to early spring, as new growth starts, and autumn is next best. In summer, a leaf spray of the iron on its own works faster.

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What’s in the Bundle

Iron Chelate, 500 g. A dark reddish-brown powder with 6% iron, held by EDDHSA, a close relative of EDDHA. It keeps iron available from about pH 4 to 9, so it works in the alkaline, limey soil where ordinary iron gets locked up, and it dissolves fully. Our iron chelate guide covers it in detail.
Humic Acid Powder, 500 g. Potassium humate with at least 80% humic acid and 10% potassium (K₂O). It’s a soil conditioner rather than a fertiliser. It holds onto nutrients such as calcium, magnesium and iron, and at low rates it may help plants take up more of the nutrients you apply. Our humic acid guide has the details.

Humic acid holds iron partly by chelation, the same way an iron chelate does, though its grip is weaker than a synthetic chelate’s. In this bundle, the chelate supplies the iron and the humic acid backs it up.

There’s research behind the pairing. A review by Italian plant scientists found that humic substances can hold iron in forms roots can use and switch on the root’s own iron-uptake system, though most of that evidence comes from controlled experiments rather than real soil. And in a Spanish trial on lemon trees, mixing humic substances into Fe-EDDHA, the close relative of our EDDHSA, improved iron uptake compared with Fe-EDDHA alone, and improved fruit weight too.

When to Use It

Iron shortage has a look of its own. New leaves come through pale yellow with green veins, while older leaves stay green. It’s most common in alkaline or limey soil, near concrete, with hard water, and in citrus and acid-lovers like azaleas and gardenias.

Older leaves yellowing first? That usually points to magnesium, not iron. Our Magnesium Sulphate fixes it.
Whole plant evenly pale? It’s usually short of nitrogen. Our urea guide covers that.
Not sure? Our guide to yellow leaves with green veins walks you through it.

How Much Humic Acid and Iron Chelate to Use

⚠️ Note: More Iron won’t green plants any faster. Humic acid can go on more often, but not Iron. Halve both for seedlings, indoor plants and sensitive plants, and don’t go higher on trees.

Humic Iron rates by use
Use	Humic acid	Iron chelate	How to apply	How often
Pots & containers	1.2 g per litre (12 g in a 10 litre can)	2 g per litre (20 g in a 10 litre can)	Use it in place of a normal watering, enough to wet the whole pot	Both together in spring. Iron again after 4 to 6 weeks if new leaves are still pale. Humic acid alone every 2 weeks
Garden beds, roses & shrubs	1.2 g per m²	5 g per m²	A 9 litre can covers 2 m², with 2.4 g of humic acid and 10 g of iron chelate. Pour onto moist soil over the root zone, then hose it in	Both together in late winter or early spring. Iron again after 6 to 8 weeks if needed. Humic acid alone every 2 weeks
Lawns	1.2 g per m²	1 g per m²	A 9 litre can covers 10 m², with 12 g of humic acid and 10 g of iron chelate. Keep it off paving	Both together in spring and autumn, if new blades come through yellow. Humic acid alone every 2 to 4 weeks
Citrus & fruit trees	1.2 g per m² of canopy (about 8.5 g for a tree 3 m across)	Young trees 5 to 10 g. Mature trees 50 to 100 g	Dissolve both in 10 to 20 litres of water, pour into a shallow trench or ring of holes around the drip line, then water in	Both together in late winter or early spring. Citrus can have a second iron dose in summer. Humic acid alone every 4 weeks, spring to autumn
Hydroponics	2 to 6 g per 100 litres, added to the diluted solution, never to the calcium (A) tank	3 to 5 g per 100 litres, usually in the A tank	Don’t combine them in one stock tank. Jar test first	Each fresh batch
Leaf spray	Leave it out	1 g per litre, up to 1.5 g on fruit trees	Spray young leaves late in the afternoon, below 29 °C. Wet both sides and avoid ripening fruit	Every 2 to 3 weeks while new leaves are pale

Water every dose in straight away. Sunlight breaks iron chelates down.

How much of each do you need?

Pick what you’re treating, then slide to your can, area or tree.

Watering can: 10 L

Humic acid12 g

Iron chelate20 g

Water10 L

Iron doses per 500 g25

A 10 litre can: 12 g of humic acid and 20 g of iron chelate. Use it in place of a normal watering, enough to wet the whole pot.

Humic acid on its own every 2 weeks while plants are growing. Add the iron in spring, and again after 4 to 6 weeks if new leaves are still pale.

The 500 g of humic acid covers 41 doses this size.

Weigh a level teaspoon of each powder once on kitchen scales, and you’ll know how many spoons make a dose. Tree doses use canopy width, the spread of the branches. Halve both for seedlings and indoor plants.

How far one bundle goes
Use	Iron chelate (500 g)	Humic acid (500 g)
Pots	25 cans of 10 litres	41 cans of 10 litres
Garden beds	100 m², once	About 400 m²
Lawns	500 m², once	About 400 m²
Citrus & fruit trees	5 to 10 mature trees	58 doses for trees 3 m across

Humic acid goes on more often, so on pots, beds and lawns it usually runs out before the iron. Both come separately in 500 g and 5 kg packs when you need a top-up.

Can They Go in the Same Can?

Yes. Both powders dissolve fully, and in the lemon trial above, Fe-EDDHA went on mixed with humic substances. The order matters, and our two guides agree on it: humic acid goes into the water first, before anything else, and iron chelate goes in last.

Mix it fresh, though. Potassium humate is alkaline, around pH 9 to 11 in solution, and one humate maker lists pH 10 to 11. Fe-EDDHSA is most stable near pH 7 and holds iron from about pH 4 to 9, and in strongly alkaline water, iron drops out as iron hydroxide. So make up each can just before you use it, pour it on straight away, and don’t store leftovers.

The first time, do a jar test. Mix both at the same strength in a clear jar of water, for example 1.2 g of humic acid and 2 g of iron chelate in a litre, then wait 30 minutes. If you see clumps, sludge or sediment, apply them separately: water the humic acid on first, then the iron in a second can.

Keep these out of the can:

Calcium nitrate and other calcium fertilisers. Humic acid curdles with calcium.
Strong acids, or anything at pH 4 or below. Humic acid curdles, and the chelate loses its grip on the iron.
Pesticide concentrates and spray oils.

How to Apply It

Water the soil first. Moist soil takes the mix evenly. Don’t apply it to bone-dry soil or wilting plants.
Weigh both doses. Use kitchen scales, or weigh a level teaspoon of each powder once, so you know how many spoons make a dose.
Dissolve the humic acid first. Fill the can most of the way and stir the humic acid in until it’s fully dissolved. The water turns dark brown, which is normal.
Add the iron chelate last. Stir until it’s dissolved too.
Pour it over the roots. Wet the whole pot, or cover the root zone of a bed. For trees, pour it into a shallow trench or ring of holes around the drip line, not at the trunk. On lawns, keep it off paving.
Water it in straight away. Sunlight breaks iron chelates down, and watering carries both down to the roots.
Rinse off splashes. Both can stain paving, tiles and concrete, so hose splashes off hard surfaces and leaves.
Mix only what you need. Don’t store the mixed solution.

Wear gloves and eye protection when you handle the powders, as the iron chelate’s safety data sheet advises.

A Season With the Bundle

A simple plan for the year
When	What to apply	Notes
Late winter to early spring	Humic acid and iron chelate together	The best time for iron, as new growth starts
Spring to autumn	Humic acid on its own: every 2 weeks for pots and beds, 2 to 4 weeks for lawns, 4 weeks for trees	No iron unless new leaves turn pale
4 to 8 weeks after the first dose	Iron again, with that round’s humic acid, if new leaves are still pale	After 4 to 6 weeks for pots, 6 to 8 weeks for beds
Summer	A second iron dose for citrus	For a faster fix on any plant, spray the iron on its own
Autumn	Iron for lawns, if new blades come through yellow	The next best time for iron after spring
Winter	Nothing	Wait for new growth before the next dose

Limey soil, concrete and hard water keep locking iron up, so plants growing near them may need a dose every spring.

Not Greening Up?

Look at the new leaves. Iron applied to the soil shows in new growth first, not in old leaves. Fast growers often green up in 1 to 2 weeks, and slow growers like gardenias and azaleas can take 6 weeks or more.
Check the drainage. Waterlogged or cold roots can’t take up iron. Fix drainage, let pots dry between waterings, and wait for warmer soil.
Check the rest of the feeding. Natives given high-phosphorus fertiliser often turn yellow. Switch to a low-phosphorus native fertiliser.
Give the humic acid a season. Its effects are gradual and show most in poor or stressed soil.

Frequently Asked Questions

Can I mix humic acid and iron chelate in the same can?

Yes. Dissolve the humic acid first and add the iron chelate last, make it up just before you use it, and jar test it the first time. Keep calcium fertilisers out of the can.

Do I use both every time?

No. Humic acid goes on every 2 to 4 weeks while plants are growing. Add the iron only when new leaves are pale: in late winter or early spring, and again 4 to 8 weeks later if they’re still pale.

How long until I see a difference?

Iron shows in new leaves first. Fast growers often green up in 1 to 2 weeks, and slow growers like gardenias and azaleas can take 6 weeks or more. Humic acid works gradually, over a season.

Can I spray it on the leaves?

Spray the iron on its own, at 1 g per litre, late in the afternoon below 29 °C. It works faster, but soil doses last longer. Keep the humic acid for the soil.

Is it safe on lawns?

Yes, at 1.2 g of humic acid and 1 g of iron chelate per square metre, watered in. Keep it off paving and concrete, because both can stain.

Is this bundle a fertilizer?

Partly. The iron chelate supplies iron, but the humic acid is a soil conditioner, and neither replaces your normal feeding.

Can I use it in hydroponics?

Yes, but not in one stock tank. Iron chelate usually goes in the A tank, and humic acid goes straight into the diluted solution, never the calcium (A) tank.

How should I store it?

Keep both packs sealed, cool, dry and out of direct sun, and don’t let moisture get in.

Shop the Humic Iron Complex

The bundle gives you 500 g of Humic Acid Powder and 500 g of Iron Chelate (6% Fe) in resealable packs. It suits lawns, garden beds, vegetables and herbs, fruit trees and citrus, and pot plants.

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