When did we all start using shop-bought composts?

March 13 2022

When did we all start using shop-bought composts?

This is a bit of a digression, but I though it might be interesting to look at why and when we all started using bagged composts.

Before about the middle of the twentieth century, most people made their own potting mixes, based on soil, homemade compost, leaf mould, sand, grit – whatever they had to hand or could source. They might need to add fertilizers, as the compost had to provide the right balance of nitrogen, phosphorus, potassium and trace elements. It needed to have the right amount of lime, or none; for example, if it contained too much leaf mould, it might be too acidic. It needed to be the right texture, and probably sterilised.

So the possibility of having a reliable, ready-to-use bagged compost would have been a real godsend.

This was provided by the John Innes Horticultural Institution, which was set up in 1910 as an advanced training school for gardeners, a fruit-breeding research station and an institution for horticultural experiment and research with an emphasis on plant genetics.

They needed reliable composts for their experimental plants, and rafter much research during the 1930s, they arrived at a set of formulae for different types of compost, e.g. for growing seeds, for potting-on, or for growing larger plants, shrubs and trees in containers. In 1938, as part of the war effort, they published a series of leaflets and gave radio broadcasts to publicise their new composts and other improved methods for raising garden crops. ({info from https://www.jic.ac.uk/about-us/history-of-plant-microbial-science-at-john-innes-centre/).

Incidentally, the fact that the recipes weren’t patented explains why ‘John Innes Compost’ can cover so many wildly different formulations still; and peat has been used in many interpretations of the original recipe and still is, today. The crucial ingredient was loam (soil), with the addition of peat, sand or grit, limestone (usually), and a specially formulated ‘base fertilizer’, which was mixture of organic and mineral ingredients to provide enough nutrients for a month or two.

Why peat? It was reliable, consistent, and very very cheap to produce in large quantities. It’s said to hold water better than anything else (as long as you don’t let it dry out completely, when it can be very hard to get it to take up water again!). And it can be used in the many machines that have made industrial plant growing possible – for example, in the soil-blocking machines that produce the huge numbers of plug plants bought in from the Netherlands and elsewhere, to be grown on for sale.

Since these composts were first introduced, the industry has grown beyond all recognition. Once garden centres started up in the 1970s, many manufacturers have developed large ranges of different composts for different purposes, which made it so much easier to choose the right growing medium. Most of them don’t use soil at all (which makes them much lighter – suddenly, even if you didn’t have a garden, you could just go out and buy some compost to fill a few pots and have a few plants on a balcony, or just outside the door. The convenience and predictability of these composts meant that over the years, we’ve all begun to feel that they’re absolutely necessary in order to grow anything. That’s not quite the case – but we’ll look at that in the next post.