Soil is inorganic - particles of clay, loam, sand, silt, ground minerals. It can be very fertile or not at all, depending on the particles size, mineral content and organic matter content. Most soils usually have some organic matter in it. Add more of it if your soil doesn't have enough but more isn't always better. As the organic matter decays, the released nutrients are trapped between the particles of the soil and available to plants (this is why sandy soils can't hold nutrients - they drain too well and the nutrients disappear, and also why clay soils are often fertile). Shop bought topsoil is usually the perfect loamy mix, sterilized to kill weed seeds. It already has some organic matter in it and for many plants, it is good on its own. For hungry plants, it can be better to add a little bit more. Compost is mostly organic and it is a growing medium. The traditional mixes (JI based) have peat, sand and loam. A typical MPC would be mostly peat with some sand. Peat-free composts are a mix of composted organic matter (like garden compost), coir and other ingredients. Nutrients are almost always added to composts, it can be inorganic (lime, phosphates), organic (hoof, horn) or it can be timed slow-release granules. Composted organic matter on its own is too low in nutrients - good as a mulch or to mix with a soil that needs it but not suitable as a growing medium. A typical MPC is designed to feed a potted plant for two months, sometimes for longer, and then, additional nutrients need to be added (feeding). Using compost to mix with soil doesn't make much sense. If you want to add nutrients, you can add fertilizers directly. If you want to add organic matter, there are better products for that. Although it's fine to mix used compost with soil because there is no other use for it. Woody or fibrous organic matter is usually better than compost to mix with soil to improve its structure. And here comes manure. It is usually a mix of wood shavings or chips or straw with animal waste, and this all composted. Most of the nitrogen from the animal urine decomposes during the composting process but there is still some left. Fresh urine or manure has too much nitrogen and is too strong. A composted manure typically has a very low NPK around 1-0.5-1, so it has nutrients but it can't really be considered a plant food.
@edhelka thank you! That's a lot of info and I'm going to have to read it a couple more times to take it all in.
One interesting thing I noted though is that manure is not really adding much in the way of nutrients, but it's giving the soil better structure. If that's the case, how are you adding those required nutrients? Or are you just relying on fallen leaves etc to provide it? Or is the manure/compost enough?
In pots I get the fact that there's limited nutrients available and so you are going to have to add them yourself at some point. In pots, if I understand correctly, you are also suggesting that for longer term planting you should be using topsoil with added fertilizer, be that organic (blood fish and bone) or chemical pellets, correct?
Manure is relatively low in nutrients in comparison with plant food but it has much more than compost (not counting the fertilizers added to it, just plain composted organic matter) and we usually use quite a lot of it. The nitrogen in manure is relatively quick-acting. Then there is the organic matter (straw, wood shavings, bedding from stables) which decomposes slowly and nutrients to the soil slowly. So it gives both an immediate boost and long-term effect. Plants actually don't need much nutrients. For permanent planting like perennials or shrubs, healthy soil with 3-7 % of organic matter is enough with no additional feeding. In nature, this is achieved naturally through fallen leaves and plant debris. As the organic matter decomposes (with the help of worms, fungi, bacteria and other soil life), nutrients are released into the soil and trapped there (in case of clay soils) or leached away (in case of sandy soils). Our gardens are slightly different and the natural process may not be sufficient, like in these scenarios: - Large density of plants, larger than would grow in nature - Annual planting (flowers or vegetable), plants being removed every year without allowing them to die naturally, returning a large portion of nutrients back to the soil - Growing very hungry plants (tomatoes, roses...) and high density of them - Keeping the garden tidy - removing fallen leaves, dead flowers and stalks - Growing hungry plants in unfertile soil (plants that would never grow in that soil naturally) In these cases, going for a higher percentage of organic matter in the soil and replenishing it every year may be needed (or adding artificial fertilizers). Basically, nature needs no added fertilizer, it's our messing with the ecosystem that creates that need. In pots, nutrients get used up or leached off with watering. The natural process of decomposing the organic matter is slower (not enough soil life there) and nutrients disappear with watering anyway. Using a loam/soil-based medium increases its capacity to hold water and nutrients for longer. It also prevents soil drop (pure compost drops a lot every year). The best way how to feed permanently potted plants is using slow-release fertilizer or adding a little bit of liquid fertilizer to every watering. Plants that prefer poor soil can be ok just with the slowly decomposing compost but for most plants it isn't enough. I hope it makes sense
One more point about nutrients. When we talk about nutrients from the decomposing matter, it means mostly nitrogen, although P, K and micronutrients can come from organic matter too. P, K and micronutrients are usually naturally present in most soils from mineral sources and are very very slowly through chemical reactions with acidic rain or other very long-term chemical processes made available to plants. Compost has nothing like that.
You already have a lot of good information now. The only other thing I would add about manures is they add a lot more humus to the soil. Humus is actually the brown sticky liquid you get from manure and compost . This humus binds soil particles together to help make that open crumb structure which is considered ideal for roots. Remember also soil fungi actually breakdown a lot of the organic matter and makes nutrients available to the plant roots in a symbiotic relationship, the plants give the fungi sugars in return. There's another whole world in soil that many of us are only just learning about.
Brilliant info from Edhelka there. To geek out even further, there's also this soil chemistry term of 'cation exchange capacity,' which in practical terms means that soil organic matter, and clay, are able to hold on to nutrients within the soil, in a way that roots can easily access. With sand (which has a low cation exchange capacity), nutrients can leach straight through, and that's why we add bulky organic matter to sand.
There's a growing movement away from high-nutrient, high organic matter soils at the moment. Trendy ornamental grass and perennial plantings need to avoid grasses and thugs dominating them, without continual intervention. But if you grow them in a 'stressed', low nutrient soil, plant communities can become much more stable (and individual plants less likely to grow too lush and flop over). This mean you can pack in more floral diversity without things disappearing through competition.
"What is hateful to you, do not do to your neighbour".
Thanks for that interesting input @Loxley. I'm not at all surprised that there is a movement away from overly fertilised soils in some quarters. I think there seems to be a lot of that happening in all quarters, be it minimalism or something else similar.
Posts
As the organic matter decays, the released nutrients are trapped between the particles of the soil and available to plants (this is why sandy soils can't hold nutrients - they drain too well and the nutrients disappear, and also why clay soils are often fertile).
Shop bought topsoil is usually the perfect loamy mix, sterilized to kill weed seeds. It already has some organic matter in it and for many plants, it is good on its own. For hungry plants, it can be better to add a little bit more.
Compost is mostly organic and it is a growing medium. The traditional mixes (JI based) have peat, sand and loam. A typical MPC would be mostly peat with some sand. Peat-free composts are a mix of composted organic matter (like garden compost), coir and other ingredients. Nutrients are almost always added to composts, it can be inorganic (lime, phosphates), organic (hoof, horn) or it can be timed slow-release granules. Composted organic matter on its own is too low in nutrients - good as a mulch or to mix with a soil that needs it but not suitable as a growing medium. A typical MPC is designed to feed a potted plant for two months, sometimes for longer, and then, additional nutrients need to be added (feeding).
Using compost to mix with soil doesn't make much sense. If you want to add nutrients, you can add fertilizers directly. If you want to add organic matter, there are better products for that. Although it's fine to mix used compost with soil because there is no other use for it. Woody or fibrous organic matter is usually better than compost to mix with soil to improve its structure.
And here comes manure. It is usually a mix of wood shavings or chips or straw with animal waste, and this all composted. Most of the nitrogen from the animal urine decomposes during the composting process but there is still some left. Fresh urine or manure has too much nitrogen and is too strong. A composted manure typically has a very low NPK around 1-0.5-1, so it has nutrients but it can't really be considered a plant food.
One interesting thing I noted though is that manure is not really adding much in the way of nutrients, but it's giving the soil better structure. If that's the case, how are you adding those required nutrients? Or are you just relying on fallen leaves etc to provide it? Or is the manure/compost enough?
In pots I get the fact that there's limited nutrients available and so you are going to have to add them yourself at some point. In pots, if I understand correctly, you are also suggesting that for longer term planting you should be using topsoil with added fertilizer, be that organic (blood fish and bone) or chemical pellets, correct?
Plants actually don't need much nutrients. For permanent planting like perennials or shrubs, healthy soil with 3-7 % of organic matter is enough with no additional feeding. In nature, this is achieved naturally through fallen leaves and plant debris. As the organic matter decomposes (with the help of worms, fungi, bacteria and other soil life), nutrients are released into the soil and trapped there (in case of clay soils) or leached away (in case of sandy soils).
Our gardens are slightly different and the natural process may not be sufficient, like in these scenarios:
- Large density of plants, larger than would grow in nature
- Annual planting (flowers or vegetable), plants being removed every year without allowing them to die naturally, returning a large portion of nutrients back to the soil
- Growing very hungry plants (tomatoes, roses...) and high density of them
- Keeping the garden tidy - removing fallen leaves, dead flowers and stalks
- Growing hungry plants in unfertile soil (plants that would never grow in that soil naturally)
In these cases, going for a higher percentage of organic matter in the soil and replenishing it every year may be needed (or adding artificial fertilizers). Basically, nature needs no added fertilizer, it's our messing with the ecosystem that creates that need.
In pots, nutrients get used up or leached off with watering. The natural process of decomposing the organic matter is slower (not enough soil life there) and nutrients disappear with watering anyway. Using a loam/soil-based medium increases its capacity to hold water and nutrients for longer. It also prevents soil drop (pure compost drops a lot every year). The best way how to feed permanently potted plants is using slow-release fertilizer or adding a little bit of liquid fertilizer to every watering. Plants that prefer poor soil can be ok just with the slowly decomposing compost but for most plants it isn't enough.
I hope it makes sense
P, K and micronutrients are usually naturally present in most soils from mineral sources and are very very slowly through chemical reactions with acidic rain or other very long-term chemical processes made available to plants.
Compost has nothing like that.
Now to just figure out what to plant in all this soil!
There's a growing movement away from high-nutrient, high organic matter soils at the moment. Trendy ornamental grass and perennial plantings need to avoid grasses and thugs dominating them, without continual intervention. But if you grow them in a 'stressed', low nutrient soil, plant communities can become much more stable (and individual plants less likely to grow too lush and flop over). This mean you can pack in more floral diversity without things disappearing through competition.
When you don't even know who's in the team
S.Yorkshire/Derbyshire border