Page 28 - Simply Vegetables Autumn 2023

media for drainage and the amount and type used depends on the media. There are a wide range of sands available varying in type and size and it is important to choose the right one otherwise it can negatively affect plant growth. The sand should be lime free and a reasonable coarse one as fine sand can block the pores in the soil causing poor aeration and waterlogging. Soils Many organic books and magazines suggest making your own growing media with a mixture of garden soil, leaf mould and home-made compost. Although this may be successful for some easy to grow plants a number of problems can arise. Both the soil and homemade compost could contain weed seeds which are likely to grow and either could contain diseases and possibly small soil pests unless partially sterilised.
The use of soil in growing media is fine and has been used many years, in fact hundreds of years since we have grown in containers. The important point is that it is the right type of soil and not any old soil from your garden or elsewhere.
The ideal soil is a medium to heavy, preferable a turfy one, this was established by the John Innes Research Institute back in the 1930’s by Johnson and Newell. If
the soil is sandy, it is too free draining and leaches out nutrients, if a clay soil the drainage is poor and plants produce poor root growth or die from waterlogging, or the media sets like concrete if it dries out.
So, what soil can we use? The recommendation is for stacked turf of a medium to heavy loam, try contacting a turf supply company and see if they sell the offcuts or damaged turf. If so, buy a load and stack it in a heap, cover and leave for 12 months, if you have some well-rotted manure stack it in layer of turf and manure. Whilst it is rotting take a soil sample and check the pH (ideally it should be 6.3 Slightly acid), if it is lower than this add slightly more lime, if higher use less lime when mixing.
When you break open the stack slice down the sides and sieve the soil through a 9mm sieve, if you have a soil shredder the soil can be shredded which is a lot quicker!
Soil Sterilisation
Or correctly I should have stated partial sterilisation as if fully sterilised it would kill the good soil flora and fauna which we need. Very small amounts can be done
in the microwave (but ask the head chef first!); larger quantities need a different method. The one I used many years ago consisted of a 25 litre metal oil drum into which I put an old grate, water was added up to the grate level and it was then
placed onto an old hot plate. The soil to
be sterilised was put into a hessian sack which was supported over the grate and the hot plate switched on which heated the water. As the water got hotter it turned to steam and passed through the soil steam
Tomatoes showing poor leaf colour
sterilising it. It worked very well, and I rarely had any weeds grow or any pest and disease problems and my parents paid for the electricity!! The bag should nearly seal the drum so that the steam passes through the soil and not straight out of the drum. The soil was allowed to dry a little before mixing with peat, sand and John Innes base fertiliser to make John Innes compost. I think it took around 45 minutes but if you have a thermometer leave it steaming until the soil temperature is 80°C for 10 minutes. Insects, diseases, most viruses and weed seeds are killed at 80°C if held for 10 minutes.
Growing Media Mixes
There are several mixes that could be made which I will consider next. I will start with the old-fashioned John Innes Composts; this is like going back to the future as these were developed by the John Innes Institute in 1937 and could become more commonly used in the future. They were developed
as a general-purpose growing media for
a very wide range of plants and will be suitable for most if not all vegetables. The original J I recipe contained peat, but this could be substituted by either coir or leaf mould or at a push if good quality by well- rotted homemade compost. The two J.I recipes are set out below:
John Innes Seed Compost
2 parts sterilised medium loam
1 part peat or coir
1 part coarse sand
(all measured by bulk / volume)
The peat or coir should be sieved through a 9mm sieve to remove any lumps, the sand / grit should be lime free, and coarse with 60% of the particles between 1.5 and 3mm in size.
To the above add 42.5 gms of superphosphate and 21 gms of chalk per bushel, or for larger quantities of compost, 1.10kg of superphosphate and 550 gms
of chalk per cubic meter. A bushel is .035 cubic meter!
It is recommended that the main ingredients are sieved first and then mix them thoroughly with the superphosphate and chalk.
John Innes Potting Compost
7 parts sterilised medium loam
Sieved bark
3 parts peat or coir
2 parts coarse sand
(all measured by bulk / volume)
For JIP 1 to the above add 113 gms John Innes Base fertilisers and 21 gms chalk
per bushel, or for larger quantities 2.75 kgs John Innes Base fertiliser and 550 gms chalk per cubic meter. For JIP 2 add double the above fertiliser and chalk and JIP 3 add triple the above fertiliser and chalk.
The John Innes Base fertiliser can be brought ready mixed, or you can make your own, the recipe is below all by weight:
2 Hoof and Horn 3 mm grist
2 Superphosphate of lime
1 Sulphate of potash
Again, mix thoroughly to ensure all plants get the correct nutrients, the analysis of
the above for those of you interested is nitrogen 5.1%, soluble phosphoric acid 7.2%, potash 9.7%.
When the soil has been allowed to dry
the ingredients can be mixed, ensure you do not contaminate the sterilised soil by using dirty tools / equipment and putting in a dirty shed etc. it is wise to use the compost within 2 to 3 months of mixing as the fertilisers will start to release the nutrients.
Alternative Growing Media
Back in the 1970’s the peat based multipurpose compost started to become popular and replaced the John Innes,
this was partly because good loam was becoming hard to obtain. Some of the multipurpose composts were proprietary mixes like Levington but there were recipes for homemade mixes. One of the most widely used and well-known was the U.C composts which were developed at the University of California, these were studied by the research stations in the U.K and the GCRI loamless compost was developed;
28 Simply Vegetables