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By January 27, 2018 0 Comments Read More →

Compost Recipes

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Elizabeth McCorquodale mixes up some sustainable compost recipes for all your different gardening needs

Plunging a hand into a bucket of well-rotted, home-made compost or leaf-mould is always a very satisfying thing. Plunging it into a bag of proprietary, shop-bought potting mix is usually a bit of a disappointment, and that disappointment often comes with a hefty price tag. I confess to a real dislike of buying bags of potting mix of any description, not only because they are so costly, but also because I just don’t know what is in them or where it came from, so I prefer, whenever I can, to make my own.

Most proprietary mixes contain a base of either peat or coir, with the addition of vermiculite for drainage and/or water retention, and sometimes some sort of composted organic matter such as lightly composted bark. Some of these mixes are rather dirty, some are difficult to wet or re-wet once they have dried out, and some have so little fine organic matter that water just drains straight through them. Also, very few of them come with impeccable environmental credentials.

The ideal potting mix is so much more than just a substance to physically support the roots of a plant and hold it upright. It must also have a good balance of water retention and drainage, a good cation exchange capacity (which simply means that it has the capacity both to hold onto and release nutrients), and it should be fairly stable, both in physical and chemical composition.

Whatever combination you opt for, a thorough mixing of all the ingredients is essential.

Garden soil is the obvious choice for use as a base for a potting mix, but unless you have a large pile of good, friable soil that is relatively weed and pathogen free, you may have to look elsewhere. That said, small quantities of garden soil can be harvested from unexpected places. Molehills, or the soil from building or planting holes, will act as a good base, but be sure to remove as much detritus from the soil as you can.

Loam is at the heart of many home-made potting mixes. It is made from grass turves cut into sections and stacked upside down until they rot down to a soil-like consistency. Like any composting process, the trick to a speedy conversion of turves to soil is to maintain moisture and heat within the heap without excluding air; the hotter the heap, the quicker the process. Loam is only moderately nutritious, but its great strengths are its ability to hold nutrients which are added to it ‒ it has a good cation exchange capacity ‒ and its texture and ability to hold water and to drain reasonably well.

Leaf-mould is lovely stuff, and it is so easy to make. Just fill sturdy bin-bags to the top with leaves as they fall, tie the top to keep out the winter rains, poke holes around the base to allow a little air exchange, then leave them in the corner for a year. The resultant soil conditioner will be rich and earthy, and just perfect for using in your mixes. It isn’t terribly nutritious, but it does have a good load of microorganisms that help to fight off pests and disease, and it holds moisture well and is easily re-wet if it

Loam, garden soil and composted bark.

dries out.

 

Well-rotted kitchen and garden compost is more nutritious than leaf-mould and makes a very good base for most mixes. If, however, you are using it as a base for seeds and seedlings, combine it with equal quantities of loam or leaf-mould or it may be too rich for the delicate needs of these tiny plants. The nutrient value of compost is directly linked to the raw ingredients, and the speed with which it rots down is directly linked to how small you chop the raw materials and how you build your heap. The biggest mistake in compost making is building your heap in a cold, dark corner of the garden; give it a sunny spot, layer it well and water it occasionally, and your heap will thrive.

 

Well-rotted compost makes a good base for your own soil mixtures.

It is difficult to think of a better, more environmentally friendly soil conditioner than composted woodchips and composted bark. They are usually the by-products of several industries, can be locally sourced, and have all the qualities that you need in a soil conditioner once properly composted. Composted woodchips and composted bark make absolutely wonderful stuff, but unless you want to wait a long time, you will have to build your compost pile high! Go for a heap at least 1.5m × 1.5m, and water it very well as you lay it down ‒ all the chips should be wet. When you have reached a height of around 1.5m, sling a tarp over the whole thing, tie it down snugly and leave it to cook for a year. The resultant soil conditioner will be crumbly and sweet smelling, and ideal for use as a base in your mixes, and is a far superior replacement for peat.

Well-rotted manure is rich and nutritious and can be sourced in large quantities, but for container gardening of any sort – as opposed to using it as a garden soil conditioner or a mulch – it should be composted for at least two years. This ensures that it has fully broken down and mellowed enough to come into safe direct contact with the roots of containerised plants. Keep your manure heap nice and hot in order to kill as many weed seeds as possible, and turn it occasionally to break it up to ensure that any straw or other bedding rots down efficiently.

Worm compost has much the same virtues as a good quality, well-composted kitchen and garden compost or ordinary quality manure, but with a really lovely, fine texture. If you can make enough worm compost you are well on your way to a very fine potting mix.

Sharp sand or fine grit are the best ways to introduce drainage into a container mix. Sharp sand can be oddly difficult to find, as so many sands are just too fine grained to do much good, but a trip to your local builders’ merchant should offer up some options. To do the job well, the grains must be big enough to be rough and grainy between your fingers. If you can find a good, cheap source of fine grit or small stones, get a large bag, as it will never go to waste, and of course, unlike organic matter, it will never sour. <

TO PASTEURISE OR NOT TO PASTEURISE

For some this is a tricky question, but for me it is dead easy. I only pasteurise a soil substance that will be used for seed sowing or transplanting delicate seedlings. I figure that if I have got the mix right and the growing conditions are pretty good, then the plants will be resilient enough to cope with any weed or disease competition that may arise from their growing medium.

Pasteurising small quantities of soil is easy enough: half an hour in an oven set just above 82°C will kill most weed seeds and most harmful pathogens. Unfortunately, it will also kill off most helpful microorganisms, but this trade-off at the seed/seedling stage is worth making. Simply dampen the compost, pile it into a deep oven tray, cover it with foil to help retain the steam, place it in a cold oven, then turn on the oven. Begin timing once the oven has reached 82°C and let it sit at that temperature for half an hour.

Don’t be tempted to raise the temperature or to let it ‘cook’ for longer than half an hour after it has reached that temperature. At 100°C the soil will be rendered sterile, and sterile soil means that all the good fungi, bacteria and micro-beasts will be wiped out, and as we know, all those good microorganisms have a valuable job to do, so keep it to 82°C!

THE RECIPES
Compost for Seeds and cuttings

All these need very good drainage, so the proportion of drainage materials is very high – one-third of the volume of the entire mix. Once roots start to grow and the seedlings or cuttings begin to put on top growth, they will be ready to be transplanted into the next mix. < pic 10 with caption: Cuttings. >

*           One part sieved and pasteurised loam or sieved and pasteurised fine garden soil.

*           One part leaf-mould or composted woodchip or composted bark.

*           One part fine grit or sharp sand.

Compost for Potting on

This next stage needs to have a little more in the way of nutrients, but not much in the way of extra drainage.

*           One part loam or coarsely sieved garden soil.

*           One part leaf-mould or composted woodchip or composted bark.

*           One part rich kitchen and garden compost.

Compost for High-nutrient potting on

This is suitable for annual flowers and any vegetable seedlings.

*           Two parts rich kitchen and garden compost.

*           One part well-rotted manure (at least two years old) or worm compost.

Raised beds and larger containers

*           Two parts loam or leaf-mould or composted woodchips or composted bark.

*           One part rich kitchen and garden compost.

*           One part well-rotted manure (at least two years old) or worm compost.

Ericaceous Mix

*           One part leaf-mould.

*           One part composted bark and or pine needles.

*           One part rich kitchen and garden compost.

Succulents in permanent pots

*           One part pasteurised loam or garden soil.

*           One part grit.

*           One part kitchen and garden compost.

COMPOSTING TIPS

*           Keep an eye on the pH of your mixes. A pH meter is inexpensive and is invaluable for a quick check. You should be aiming for a pH of around 6.5 for most plants, though acid lovers will need a pH of about 5.5–6, and calciferous plants such as cabbages will appreciate a pH of closer to 7.5.

*           Vermiculite is a fine addition to many potting mixes; however, it is increasingly difficult to ignore the environmental impact of accepting this substance as an ingredient in our potting mixes. Vermiculite is a mined mineral that is taken out of the ground in vast quantities, often in huge opencast mines, with all their implications. It is then processed using exceptionally high (environmentally costly) temperatures to achieve the expanded little pellets that are used in horticulture, in home building and in industry. It is then loaded onto ships and transported over long distances to reach us here. As with peat, if there are perfectly acceptable alternatives, why not use them?

*           Coir is often offered as an alternative to using peat, and on the one hand it is a renewable resource and a natural by-product of another industry, unlike peat. On the other hand, it requires shipping over vast distances to reach us, and so the environmental points it gains on the one hand, it loses on the other. I would suggest that coir is probably a valuable and eco-friendly addition to potting soils when it is used in the countries where it is harvested.

 

 

 

 

 

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