Organic vs Mineral Nutrients: How They Work and Which to Choose

Walk down the nutrient aisle and the first choice you face is organic or mineral. One camp swears organic feeding is gentler and more natural; the other says mineral feeds are faster and more precise. Both are right, because they are two different ways of getting the same elements to a root. This guide explains how each one works, where each one shines, what bio-mineral feeds are, and how to choose for your growing medium. It applies to tomatoes, chillies, cucumbers, herbs, salads and houseplants in exactly the same way.

The real difference: who does the digesting

A root cannot eat a fish, a leaf or a crystal of fertiliser. It takes up nutrients as tiny charged particles, called ions, dissolved in the water around it: nitrate and ammonium for nitrogen, phosphate, potassium, calcium, magnesium, and a list of trace elements. Every feed, organic or not, ends up delivering those same ions. The difference is how they get there.

• Mineral feeds are made from salts that already contain those ions. Stir them into water and they dissolve, and the plant can use them straight away.
• Organic feeds are made from things that were once alive, or from natural rock and ash: plant extracts, fish, seaweed, worm castings, bone and blood meal. Most of their food is locked up in larger molecules that bacteria, fungi and worms in the soil have to break down before a root can use it.
• Bio-mineral feeds sit in between: a mineral base that feeds directly, with organic extras such as amino acids and plant extracts added.

How organic feeding works

Organic feeding is really feeding the soil. Bacteria and fungi in the compost eat the organic matter and release its nutrients bit by bit, and worms and other soil life turn it over. The result is a slow, steady supply that follows the plant's needs fairly well, and a compost that holds water and air better as the season goes on.

That has some clear advantages:

• It is hard to overdo. Because most of the food is released gradually, a slightly heavy dose is far less likely to scorch roots than the same mistake with mineral salts. Our nutrient burn guide shows what overfeeding looks like.
• Salts do not build up as quickly in the pot, so there is less need for regular plain-water runs to clear them.
• The compost improves rather than wearing out, which suits growers who reuse their soil.

And some limits to be honest about:

• It needs living, warm compost. Soil life slows right down when the root zone is cold, so organic feeds release less in a chilly winter tent. Our guide to keeping a tent warm in winter covers the root zone.
• It is slow to fix a shortage. If a plant runs short, an organic feed can take days to correct it. Our nutrient deficiencies guide helps you spot one early.
• It is less precise. You cannot measure exactly how much food is available at any moment.
• Rich, damp compost attracts fungus gnats if the surface stays wet. See our fungus gnat guide.

How mineral feeding works

Mineral feeds, often called synthetic or salt-based feeds, are carefully balanced blends of soluble salts. Because everything is already dissolved, the plant gets exactly what the chart says, when the chart says it. That makes them the standard choice for growing media that hold little or no food of their own.

• Fast. A change in the feed shows up in the plant within days, which makes correcting a problem quick.
• Precise and measurable. An EC meter reads a mineral feed accurately, so you know exactly how strong the mix is. Our guide to reading a feed chart explains how to mix and scale one.
• Clean in hydro. Mineral feeds leave little residue, so they will not block drippers or turn a reservoir sour. Our hydroponic systems guide covers the systems they suit.
• Made for coco and rockwool. Coco needs extra calcium and magnesium from the start, which coco ranges build in. Our coco feeding guide goes into detail.

The trade-off is that mineral feeds are less forgiving. Too strong a mix scorches leaf tips, and unused salts build up in the pot over time, which is why coco and hydro growers water through to run-off and check the EC of what drains out.

Organic and mineral side by side

Feeding the soil instead of the plant

Liquid feeds are not the only organic route. Many soil growers put most of the food into the compost at the start and top it up as the plant grows, watering with plain water in between. It is the closest indoor growing gets to a vegetable bed.

• Pre-fertilised compost. An organic mix with food already blended in carries a young plant for its first few weeks without any liquid feed at all.
• Worm castings. Mixed into compost at the rate on the bag, or spread on top as a dressing, castings add gentle food and a lot of soil life.
• Slow-release tablets and top dressings. Pushed into the compost or sprinkled on the surface and watered in, these release food over several weeks. Follow the maker's rate for your pot size.
• Mycorrhizae and microbes. Beneficial fungi and bacteria help roots reach water and nutrients. Apply them at planting or potting on so they touch the roots. They are wasted alongside hydrogen peroxide or other sterilising cleaners, which kill them; our root zone guide explains the choice between sterile and biological.

If you reuse compost, a season of organic feeding and castings will leave it in far better shape than mineral feeding, but refresh it with fresh compost and castings before replanting. Our growing media guide covers soil, coco and hydro in more depth, and our pot size guide helps you give the roots enough compost to draw on.

Bio-mineral: the middle ground

Bio-mineral feeds take a balanced mineral base and add organic ingredients such as amino acids, humic substances or plant extracts. The mineral part does the feeding and keeps the mix measurable; the organic part is there to support the root zone and soil life.

They suit growers who want the precision of a mineral feed in coco or hydro but like the idea of some organic content, and they read sensibly on an EC meter. Two things to know: they are not certified organic, and in a recirculating hydro system you should only use one that is labelled for it.

pH and EC with organic feeds

Measuring works a little differently once you go organic.

• EC reads low. An EC meter measures dissolved salts, and most of the food in an organic feed is not dissolved salts yet. A reading that would be weak for a mineral feed can be perfectly adequate for an organic one. Follow the chart and the plant rather than chasing a number.
• pH still matters, but soil is forgiving. A good compost buffers pH, and many organic growers find they barely need to adjust. If your tap water is very hard or very soft, check it and aim for the soil range in our pH guide. Our water quality guide explains hard water.
• Use organic adjusters with organic feeds. Strong mineral acids can upset soil life. Organic pH down products based on citric or other natural acids, and organic pH up, keep the whole feed consistent.
• Calcium and magnesium. Soft or filtered water can leave plants short of both whatever the feed. An organic cal-mag fills the gap for soil and coco growers.

How to choose: four questions

1. What are you growing in? This settles most of it. Soil: either works, and organic is at its best. Coco: mineral or bio-mineral is easiest. Hydro or rockwool: mineral, or a bio-mineral labelled for hydro.
2. How closely do you want to control the feed? If you like to measure and adjust, mineral gives you numbers you can trust. If you would rather set up a good compost and water, organic suits you.
3. How warm is your root zone? Organic feeding slows right down in a cold tent or a winter greenhouse. Mineral feeds keep working.
4. Do you want to grow organically? If organic produce matters to you, choose an organic range and organic pH adjusters, and check the label for certification.

Browse nutrients and boosters

Seven common mistakes

1. Using a soil organic feed in hydro. It needs soil life to work and fouls pumps, drippers and reservoirs.
2. Judging an organic feed by EC. A low reading does not mean the plant is hungry.
3. Feeding a pre-fertilised compost too early. Let the compost do the work for its first few weeks.
4. Expecting organic to fix a shortage overnight. Catch problems early, or keep a quick-acting supplement from the same range.
5. Feeding mineral salts at full chart strength from day one. Start lower and step up while the plant looks healthy.
6. Killing the soil life you paid for. Hydrogen peroxide and strong sterilisers wipe out microbes and mycorrhizae.
7. Mixing ranges. Two balanced ranges combined make one unbalanced feed.

Quick answers

What is the difference between organic and mineral nutrients?

Mineral nutrients are salts that dissolve straight into the forms a root can take up, so they work within hours and can be measured precisely. Organic nutrients come from plant, animal or mineral matter that soil bacteria, fungi and worms have to break down first, so they feed more slowly and depend on a living compost. The plant ends up absorbing the same elements either way.

Are organic nutrients better than mineral nutrients?

Neither is better across the board. Organic feeds suit soil and an easy-going routine because they are hard to overdo. Mineral feeds suit coco, rockwool and hydro because they are fast, precise and measurable. Choose by your growing medium and how closely you want to control the feed.

Do organic nutrients make vegetables taste better?

Once nutrients are broken down, a plant absorbs the same elements whatever the source, so the feed alone is not a reliable route to flavour. Variety, light levels, temperature and steady watering make a bigger difference to how tomatoes, chillies and herbs taste. Many growers prefer organic feeding for other reasons, and that is a perfectly good choice.

Can I use organic nutrients in hydroponics?

Most organic liquid feeds are made for soil and are a poor fit for hydro: they need soil life to break them down, they can coat pipes and drippers, and they make a recirculating tank prone to slime and smell. Use a mineral or bio-mineral feed made for hydro, unless a product is clearly labelled for hydroponic use.

Why does my EC meter read low with organic feed?

An EC meter measures dissolved salts. Much of the food in an organic feed is not yet dissolved in that form, so the reading is lower than the real amount of food in the bottle and tells you less. Follow the feed chart and watch the plant, and use EC as a rough check rather than a target.

Can I mix organic and mineral nutrients?

It is best not to combine two different ranges, because each is balanced on its own and the result is guesswork. Bio-mineral feeds do the mixing for you, with a mineral base and organic extras in one balanced product. If you want to switch from one type to the other, do it between crops or start the new range at a lower strength.

Do I need to feed organic soil from day one?

Not usually. A pre-fertilised organic compost carries enough food for the first few weeks, and feeding on top of it too early can be too much for young plants. Start liquid feeding when the plant begins to pale or slow down, or from the week the compost maker suggests.

Is mycorrhizae worth adding?

Mycorrhizal fungi form a partnership with roots and help them reach water and nutrients, especially phosphorus. They are most useful in soil and coco at planting or potting on, applied so they touch the roots. They are wasted in a sterile system that uses hydrogen peroxide or similar cleaners, because those kill them.