This is where I'm going to explore various horticultural topics in more depth. These topics usually begin on the facebook page (check that out if you haven't already!) but there's more space to go into details here. Please feel free to comment, publicly on Fb or direct to me using contacts below.
(This is a work in progress! I will add as I get time...)
All things to do with Compost.
First the caveat; I am naturally trying to simplify everything, not write a book! There are many exceptions to these guidelines. This is to go into the topic in more detail, not write a scientific paper. A little more knowledge is however helpful whether we're making our own composts, mixing commercial products or diagnosing crop failures.
What nutrients do plants need in order to grow? Let's start at the beginning;
N, P and K. You'll see these on compost bags listing the active nutrients.
Nitrogen - N - we associate with plant vigour and leafy growth
Phosphorus - P - flower formation, seed production,
Potassium - K - we think root systems, increased disease resistance, frost tolerance and also crop sugar content
All 3 do lots of other jobs and combine with each other!
Calcium - Ca - and Magnesium - Mg - along with many other trace elements, both combine with the main N, P and K. You notice their Absence more than their Presence.
What else do they need?
Water, light, warmth in varying degrees and at different stages in their growth.
What are we looking for in the composts we use?
This is going to depend on whether we're growing seeds, taking cuttings, potting on, or growing in containers.
Within the seed is enough 'food' for the plant to germinate; this is very obvious with a large seed like a Broad Bean where you can see the shoot growing out of the bean seed. Therefore seeds don't require any nutrients to be added to the compost.
Different species will also require varying amounts of water, light (or dark) and heat for germination to take place.
Softwood cuttings are (roughly!) the tips of the plants, grown quickly with controlled heat and humidity. They are not very robust and require a degree of care to prevent becoming limp and dying. But they do grow quickly in the correct conditions.
Semi-ripe cuttings are as the name suggests, part soft green growth, part tougher stem. They are tougher than the above, require less care and still grow fairly quickly.
Hardwood cuttings are all tougher plant material, no soft growth to go limp, taken when the plants is in a dormant state. They require very little care but take several months to produce roots, and grow enough to be planted out.
In each case, we're trying to get them to produce roots but no Added nutrients are needed other than what is naturally in soil or the contents of your compost heap.
Seed and cuttings propagation thus need no extra nutrients, but they will need clean, weed-free compost to save competition. The main requirement will be in the structure of the compost to ensure aeration to prevent water-logging and a friable material into which the roots can develop. This is why many growers mix a commercial (and therefore heat treated = free of weed seeds) compost with sand/ vermiculite etc. This reduces any nutrients in the mix, and changes the structure of the compost to allow free drainage.
Good quality seed composts will thus be low in nutrients and have the required fine, free-draining characteristics.
Clearly if the seeds have germinated in seed compost, unless you prick them out at the right time, there will be insufficient nutrients for the plants to grow. The next compost thus needs some N but also root growth support from P and K.
The level of required nutrients will depend on what you're growing and how long the plants stay in this compost before - for example - being planted out. In general, this will mean quick release fertilisers.
Growing in a container
This could be 'into a larger pot' due to various reasons. Just a few examples; Globe Artichokes which can be very vulnerable to weather, pests, diseases etc. I always grow them to a 3 litre or even 5 litre size before moving to the permanent planting site, with correspondingly richer nutrient content. Fruit trees and currant bushes; having propagated them, I don't want to plant them directly into the orchard as they will get buried under the wildflowers and grasses! So again, they are potted into larger pots, with extra nutrients.
Growing (to cropping point) in a container
I'm thinking here of tomatoes if not in a greenhouse/tunnel bed. Or early potatoes.
The nutrients need to be balanced but with weighting towards P if tomatoes, K if potatoes. There also need to be immediately available sources of food, plus medium and long-term nutrients if the plants remain in the pots for several months.
Growing (permanently) in a container
Usually this would be ornamental plants, for flowers or evergreen leaves.
Again, a mix of quick and slow release nutrients need to be available, but clearly unless re-potting annually, these plants will need additional liquid feed. The weighting of nutrient will vary - extra N if leaf growth required, extra P for flowers.