Page 27 - Simply Vegetables Autumn 2023

few hardwood may be as well mixed in with the conifer bark. The size of the bark is important as the larger sizes, anything medium or larger, increase the drainage
of the media. If too fine like powder this can block the drainage creating a wet or even waterlogged media. Any bark used in growing media should be matured and not fresh and should have been composted, also a uniform size.
Wood fibre’s This is usually shredded white wood with added nitrogen to reduce the chance of nitrogen deficiency owing
to the wood drawing nitrogen out of the media. The use of wood fibres can improve the air filled capacity of the media and is usually light in weight.
Sawdusts This can vary from a very
fine dust to small chips of wood and be
of mixed woods (not one species) once well composted it can have a peat like appearance.
Coir This is the outer husks from coconuts and is imported from Asia mainly Sri Lanka
so has a very high carbon footprint. It is usually milled to produce a fine material and is available in various grades. As it has a uniform size range it has a good air filled porosity (which means it should have good drainage and aeration). But nutrients are easily leached out so may need more feeding than peat composts. Avoid coir that is contaminated with saline water (sea water) which should not be sold for growing.
Straw The chopped straw from wheat
and barley have been trialled but have
not been consistently successful, oil seed rape has also been trialled. Straw has a good air filled porosity and can be used as part of a mixture although it can start to decompose relatively quick which changes the consistency of the compost and likely to affect plant growth.
Leaf mould I am not aware that leaf mould is available to buy so you will have to
make your own. It is often recommended in organic magazines and books as a substitute for peat in homemade growing media. It has a peat like texture and feel, contains very little if any nutrients and
I think may act very similarily to peat
in growing media. To produce good
quality well-rotted leaf mould can take 18 months to 2 years, this can be speeded
up by chopping the leaves up with a
rotary mower. The leaves should be from deciduous trees and beech and oak are reputed to be the best, but lime, sycamore, plane and other trees will likely be suitable. Composted Green Waste This is available to buy either from garden centres, online or direct from the composting sites, although it is good for applying to the soil as a mulch or digging in I do not feel it is suitable for
Newly filled leaf heap
Leca
growing media and is the cause of a lot
of the problems. If it has been composted at the right temperature it should be pest, disease and weed free but does all of the material reach 70°C?
Mineral Materials These are usually added to improve the drainage and / or hold water, although they are sterile and often light in weight, they are expensive and most have a very high carbon footprint
as they are produced using very high temperatures and transported over long distances.
Perlite A naturally occurring rock, mined and heated to very high temperature (approx. 1200°C) causing it to expand
and become highly porous. It is available
in various grades and is used to improve drainage and holds some water. Perlite is used in mixture at between 10 to 20% by volume.
Vermiculite Another naturally occurring rock that is formed in plates and again heated to very high temperatures to produce the material used in growing media. It is used at between 5 to 15%
by volume in media and also as a seed covering for certain seeds. Again, it is available in grades from fine to coarse. Other materials The following have been tried as growing media either alone or in mixtures rockwool, zeolite, clays (i.e. Leca (clay balls - see photo)), lignite’s, pumice, pulverised fuel ash (i.e Lytag or Hortag) and oyster shell.
Sands Sands are used in many growing
Progrow
Simply Vegetables 27