NPK and other ways of feeding plants

bédé · April 2023

If we ate just whole animals, we would have enough nutrients to sustain us. (Just if, I am not proposing a 100% meat diet.)

We could apply a similar logic to plants. If a plant was fed on just the products of other plants, would anything extra be required. (Perhaps needing to say that the best source of food for any one type of plant might be the same type of plant. But in realistic terms, a diversely sourced garden compost or leafmould would suffice.)

In a farming economy, where vegetable products are taken off the fields and sold, the fertility of the soil needs to be replenished. But in a closed-loop garden economy, do we really need to add fertiliser.

Adding fertiliser is a constant response on these forums to many plant health problems. But is it really the answer, or is it part of the problem?

Dovefromabove · April 2023

Is your initial sentence the case? … what about vitamin C … obtained from plants and a lack of it can cause severe health problems

https://www.healthline.com/nutrition/10-nutrients-you-cant-get-from-animal-foods#TOC_TITLE_HDR_2

thevictorian · April 2023

You'll have to forgive me if the specifics aren't entirely correct but I read a few years ago about Korean farmers that make specific plant fertilisers by soaking said plant in water and over time, developing a potent fertiliser (thinks it's called Jadam). It echoes the specific nutrients for said species but it always bothered me that you would have to have a strong mixture to give the plant everything it needed in the same quantities. I do like the basics of the idea though and am exploring it more this year with some homemade liquid feeds.

As for fertilisers in general in our gardens, I do think they are overused. We need to remember though that every weed we pull up removes nutrients from the soil that aren't replenished. If we chop and drop then you do build some replenishment into it.

Jenny_Aster · April 2023

This is where the old days of animal husbandry, arable and market gardening was just perfect, absolutely nothing was wasted. Animals grazed the fields and while doing so they fertilised the soil, in return the soil giving up it's goodness for animal feeds, nature and life in perfect balance.

There's a sort of magic going on, a magic that we take for granted. My geranium seedlings this morning had developed the geranium smell. The plants have only got 3 pairs of leaves, just where did they get that smell from? They were only a very tiny seed which must have had the minutest of DNA. It's mind blowing when you start to ponder.

Nollie · April 2023

In a natural ecosystem, it’s not only decaying plant matter available to plants but the rotting corpses of dead animals, the regular droppings of the living ones, the discarded shells of birds etc. In a ‘closed-loop’ or artificial construct that is a ‘garden’, the latter, not so much. So adding blood, fish and bone and animal manures in addition to plant-derived matter (could, arguably) create a more balanced system.

Similarly, adding compost derived from vegetable matter as a mulch also mimics the natural system where it may otherwise be lacking because, for example, you have few deciduous trees around.

All this should be sufficient to feed the soil and your plants unless you have a specific nutrient deficiency or problematically extreme pH, in which case certain additional amendments may be required, whether that be N, P, K or a particular micronutrient.

However, gardeners generally want their showy flowering plants and fruit trees to perform better than nature which is why, for example, we might add a slow release fertiliser at the start of the season and a high potassium feed during the flowering/fruiting season. The plant itself does not need this to be healthy but we enjoy the fruits of adding it.

I would disagree that ‘adding fertiliser is a constant response on these forums to many plant health problems’, the response can equally be ‘wrong plant wrong place’, lack of water, too much water, weather damage, you’re being too impatient give it time..

Obelixx · April 2023

It's fairly simple isn't it? In the veg plot, anyway - high nitrogen for leafy crops like salads and cabbages and higher PK for fruit and flower crops such as beans, broccoli, tomatoes, chillies etc.

I make "teas" from spring nettles for the leafy plants and from comfrey for tomatoes and curcubits and I'll be giving some to my new apple trees too. I also use the nettle tea on my citrus plants during the summer months with a drink or two of diluted Epsom salts for magnesium. From autumn thru to spring they need a higher PK so get a specialist feed or comfrey tea if I have any left.

Other than that I feed the soil by adding well-rotted garden compost and/or manure depending on what I'm going to be growing in a given bed.

GardenerSuze · April 2023

I have added no nutrients at all to my garden this spring other than some feed for a rose. I have clay soil and with rain it does well without.
The worst thing is over feeding it makes growth soft and prone to pest and disease.

I watered some hanging baskets for a client over several weeks. They had left a well know feed that is bright blue, it stained my hands and then I found out that it wasn't benificial to the plants anyway.
Always learning.

Winston_The_Gravity_Man · April 2023

I've often mused on whether compost heaps are really necessary other than to keep gardens, etc, looking neat and tidy. Why not just cut up foliage, not roots and seeds obviously, and let them rot where they fall ? Surely more wildlife friendly and with a reduction in energy expenditure because of no trips backwards and forwards to the compost heap. There will be a nett loss of nutrients but that can be mitigated by replacing them by other means which many gardeners do anyway.

Nollie · April 2023

bédé, as a chemist, you may be interested in the following article - and I would be interested in your thoughts of the ‘traditional’ V ‘contrarian’ approaches. I must say I’m inclined to side with the contrarians.

I cannot speak for the credentials of the Canadian author, who claims a background in chemistry and biochemistry, but food for thought..

https://www.gardenmyths.com/best-npk-ratio-growing-plants/

bédé · April 2023

Dovefromabove said:

Is your initial sentence the case? … what about vitamin C … obtained from plants and a lack of it can cause severe health problems

It's difficult, but possible if you eat enough offal (an awful word, but better than the American "organ meat").

It was a throw-away opening statement. I thought of Calcium and Phosphorus because we don't eat bones, but htat might have slowed down my getting onto the main subject, plants. I did find an answer though, animals' babies' food: milk and eggs.

bédé · April 2023

thevictorian said:
Korean farmers that make specific plant fertilisers by soaking said plant in water

MontyDon likes lovage-water. I put a little on my compost heap but don't do foliar feed. But I like the idea of the "same plant".

NPK and other ways of feeding plants

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