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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 keep adding as I get time...)

All things to do with Compost.

First the caveats; I am naturally trying to simplify everything, not write a book! (although I realise I keep adding bits to this screed...)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.

I am also only considering peat-free composts.


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 - associated with plant vigour and leafy growth

Phosphorus - P - think root systems, flower formation, seed production,

Potassium - K -  helps general plant vigour,  increased disease resistance, frost tolerance, fruiting 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.

The pH value - whether a soil is acidic or alkaline - will have a great effect on whether the nutrients are available to the plant. If you have ever added lime to the cabbage patch, as brassicas like an alkaline soil, you will have seen the difference!

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, assuming you're pricking out the seedlings.

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; free-draining, friable ('easily crumbled') compost.

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 totally 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 give them the right conditions to produce roots, and until they have roots, they don't need extra nutrients.

Seed and cuttings propagation  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.

Potting on

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. Commercially, this will mean quick release fertilisers.

Too much N at this stage will lead to 'leggy' plants, which organic growers avoid! Plants which are forced, grown too quickly with excess fertilisers, will be more prone to attack from disease, pests and poor weather.

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 until they are large enough not to 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.

I mix well-rotted manure in whatever compost I'm using, for all plants in this 'growing on' group, but in any case, these plants require a slower release of nutrient over a longer time. We also need to consider the trace elements which are available in good soil and ensure these are in the compost used.

What materials are in compost?

Base material

Loam - a balance of clay, silt and sand particles containing fully decomposed organic matter.

The sort of dark crumbly soil we all yearn for! When you see composts with 'John Innes' mentioned, they will contain loam.

Molehill soil - hopefully (because it's where the worms might be for the moles), this will be a nice loamy soil! And does mean instead of getting cross at the moles, you thank them for digging it up....

Garden compost - a bit of an unknown in regard to nutrients, but if you've made it with a good mix of materials (see below) it'll be perfect as all your new plants will be 'introduced' to the soil in your garden.

Low nutrient bulk

Leaf mould - some plants won't grow happily without some leaf mould; think of plants growing in woodland habitats. Leaves are 'spent' parts of the tree and thus low in nutrient.

Coir - produced from the outer, fibrous husks of coco-nuts. I'm not that comfortable with the texture of coir, but others will swear by it.

Composted bark - another waste product. It's important that it is composted otherwise the breaking down of the bark will use up all nutrients in the area.

Stuff for drainage

There's the traditional crocks - bits of broken earthenware pots - used in large semi- or permanent container planting.

In the compost itself, horticultural sand (which means it has been washed free of salt) or fine grit may not be perfect ethical solutions but are certainly better than using polystyrene granules.

In a a large container, bark may provide drainage, but remember it will also use up N in the breaking down process, and once that process is done, obviously the drainage is less...


I'm putting green waste compost from county recycling schemes in this category, because it's often an unknown material! Some firms seem to quantify their compost, producing consistent mixes, some seem to produce random compost which might be all coniferous, or all household green waste and so on.

The use of these composts may vary according to their mix.


In bought composts, this will probably be some artificial fertiliser.

In home produced composts, manure of some type is normally used. This can vary considerably and unless you test every batch, the exact nutrient quantities and pH value will be unknown.

(Some people will use 'blood and bone' fertilisers which will have more concentrated nutrients, for example dried blood has 12% N rather than 0.6% in the same amount of cow manure. But I'm a life-long vegetarian! And you don't get the valuable humus contained in manure.)

Manure should always be 'well-rotted' rather than fresh to avoid N burn on young growth, and so that the bedding material has already or is in the process of breaking down. 

Too much manure will gradually make the soil more acidic, so if you need more nutrients you may also need to add lime in alternate years, Note; not together!

Garden Lime is made from pulverized limestone or chalk, sometimes in granular form. Do not use Slaked or Hydrated Lime!

Cow muck; somewhat sloppy until very well rotted and dried out! Has an acidifying effect on soils. 

N 0.6%   P 0.4%   K 0.5%

Horse muck; there will be more bedding in this than cow muck, whether straw or sawdust, giving a firmer material.

Less likely to have unwanted chemicals in the manure. Goat muck has very similar values of minerals and trace elements.

N 0.7%   P 0.3%   K 0.6%

Pig muck; probably the worst aspect is the apalling smell...only tried this once, very soggy!

N 0.8%   P 0.7%   K 0.5%

Chicken manure; note the high N content which can burn young growth, although comfrey seems to cope. Best added to the compost heap, speeding up the decomposing process. 

N 1.1%   P 0.8%   K 0.5%

Sheep manure; note the high K content which is very useful for root crops. Probably not so easy to collect, however if you do, try putting in a mesh sack in the water tub, for an excellent liquid feed.

N 0.7%   P 0.3%   K 0.9%

Rabbit manure; obviously only in small quantities, but has N and P in high amounts. Try bagging and adding to the water as above or using as a nutrient rich accelerant in the compost heap.

N 2.4%   P 1.4%   K 0.6%

Your own garden compost should have approximate values of;

N 0.5%   P 0.27%   K 0.8%

What do I use?

These are some mixes I have used for several decades.

Seed compost

1 part leaf mould/ composted bark/ coir - low nutrient

1 part loam (basic good soil)

2 parts sieved garden compost (or bought)

1 part horticultural sand or fine grit - free-draining

Large seeds

1 part leaf mould/ composted bark/ coir

1 part loam/ molehill soil

1 part garden or bought compost

Potting on

1 leaf mould, composted bark, or coir

2 loam or molehill soil

2 garden compost or bought compost

1 sand or grit

Cuttings mix 

4 leaf mould, composted bark, or coir

1 garden compost or bought compost

5 sand or grit - Must be free-draining

Container compost

1 leaf mould, composted bark, or coir

1 loam or molehill soil

3 garden compost or bought compost

Rich Mix,

add; eg potatoes or tomatoes in containers

1 well -rotted manure or worm casts

Bought composts

The problems;

The cost. 

The cost often seems excessive, particularly when made from recycled household garden waste, waste bark from the forestry industry and so on.

It should be cheaper, while those digging up peat bogs should be heavily fined...!

You can find cheap options in some supermarkets, all in those delightful non-recyclable plastic bags of course...and often the quality is not brilliant, or should I say Consistent - which is irritating.

The best products are definitely expensive. This saddens me as clearly all gardeners should be encouraged to shun peat. (for habitat preservation, with it's associated flora and fauna, for natural flood water control, and as a carbon sink)

The texture.

The worst products are either far too coarse for seeds or young plants, or far too dense and compacted for growing anything! Others are so free-draining, with no 'body' that they simply don't hold either moisture or nutrients. And some  - I have found this particularly with high coir content composts - appear dry on the surface but are in fact water-logged at root level.

The nutrient content.

This is tedious as often absent or too 'rich' or just the wrong type - and you're probably not going to know there's a problem until the plants fails in some way!

The solutions;

The best I have tried was definitely the Melcourt organic compost range. And if I only had a very small, town  garden, this is what I would use. I have tried many, many bought organic composts and have in the past grown thousands of plants ranging from alpines to trees and including water plants. Now that I grow mainly for my own uses, if I do need to buy extra material, it is mixed with my own composts.

An aside;

There is an old farming adage that the best agricultural tool is the farmers' boot - ie the farmer who walks his (or her)  land, walks round his stock, walks through his crops, will fare best; by observing the changes the growth patterns are learned, pests and diseases are spotted, mental notes are made on how the weather is affecting the crops. 

The same goes for the gardener; successful horticulture is 90% observation, spending time with your plants!

IF you do this, you will notice that this plant needs more nutrients, that one less water, more sun and so forth.

This applies to all aspects of horticulture - it's all about paying attention.

We all know people who grow excellent cut flowers or perfect cauliflowers or have fantastic roses - and often they 'specialize' in growing 1 type of plant. I might suggest (cheekily!) that actually they simply have the right conditions for that plant and are content for their one great success! But they may equally be besotted with one particular species, and thus constantly check and observe their habits, thereby learning what that plant needs to thrive best.

The people to take general inspiration from, are the ones who seem to be able to grow any and every plant - and the NGS, National Garden Scheme, provide us all with numerous fantastic gardens and gardeners to visit and talk to. Their enthusiasm is infectious and their knowledge invaluable. If there's any in your area, get out there and take advantage of this local - and thus entirely pertinent - pool of wisdom!

Gaining this understanding of what the plants need, enables us to mix our own composts. And it's really very easy, as well as remarkably effective and cheap!

Instead of burning leaves or filling green waste bags, put them in a wooden container in that shady spot where nothing grows, water well, cover  -  and forget about them for 2 years. (yep, this means you'll need 2 bins, one for Next years leaf storeage!)

Result? Your own leaf mould, without needing to own a mature, deciduous woodland...

As for the garden compost, you'll obviously be growing your own food and creating the outer cabbage leaves/ potato peelings/ apple core type of compost material! And weeding your lovely borders, with lots of easily composted annual weeds. And mowing the lawn with all those heat generating grass cuttings. And the horsey people in your area will be thrilled if you offer to take away their surplus manure (or your neighbours guinea pigs and rabbits for a smaller scale project) 

Simply set up 3 containers; one to fill, one maturing, and one to use. Layer the compost  - roughly, this is not an exact method, just avoid great wadges of one item - with your green waste materials, leave for a year and you should be able to fork out lovely dark compost. (If you're having problems, 'compost heaps' will be one of the next topics covered here!)

Liquid feeds

The nutrient values of liquid feeds does not have to be high to be effective as these are absorbed directly and quickly by the plant. Higher values will be achieved by putting a net of sheep or other 'dry' manure in your water tub, but very good results can be achieved by using comfrey or nettles;

Fill a large container - I use all the green material, stems and leaves but not roots - and pack it down well. If you just add a little water, enough to stop the material drying out,  then cover and leave for 3 weeks you will end up with a concentrated feed which you can bottle and diloute to use as needed. If you just cover with water and use from the container (again, after a couple of weeks, you get the same effect but it's quite smelly!

Comfrey Liquid N 0.014 P 0.0059 K 0.0340. High therefore in K and great for tomatoes

Nettle liquid is lower in K (but still good!) and high in trace elements.

Wood ash

This is high in Calcium, a good source of K , useful amounts of Magnesium, Sulphur, and P Phosphorous- as well as many trace elements including manganese, iron, zinc, aluminum, boron, copper.

The Calcium element is the same Calcium carbonate as in bought garden lime, so it is excellent for reducing acidity.

K, Potassium helps bulbs store food in the bulb for the dormant period and gives a boost against fungal attacks - both important factors for next years' flowers!

It takes effect quickly, so don't apply lots, but a handful around the brassicas will really benefit them if you have acidic soil. Asparagus, tomatoes also appreciate it.

AVOID using on plants that like an acidic soil or a low pH; Blueberries and potatoes for example.

You can add wood ash to your compost heaps as well.

I haven't tried this - yet! - but apparently a sprinkling of wood ash on your pond will control algae; I will post the results when I try that this autumn!

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