Seed trays, modules and pots
21.08.2023 - 12:04 / theunconventionalgardener.com / Emma Doughty
Soil isn’t one thing, it’s a collection of different things that come together to make the life-giving, plant-growing ‘dirt’ that we love. We have a tendency to poison it, cover it over and generally forget that it’s there, but good soil is the heart of a good garden and something we should pay a lot more attention to.
Mineral soils
Most soils are mineral based, made from mineral particles that are weathered away from the underlying rock. (Weathering is the collective term for various natural processes that gradually break down rock – it’s not the impervious, eternal substance we generally believe it to be). Soil is therefore a product of the local geology, and you have to live with what you get.
The texture of mineral soils depends on the levels of three classes of mineral particles. Sand particles, which are mainly quartz, are the largest – they range from 0.06 mm to 2.0 mm in diameter. Even the smallest sand particles feel gritty, and they are non-porous. Their ability to hold water depends very much on their size – coarser sand particles make soil very free-draining.
Silt particles are smaller, between 0.002 mm and 0.06 mm across, and behave very much like sand. They can hold more water, but they can’t form stable crumbs (clumps of soil particles) and can be hard to manage. Some silt particles are less inert than sand and act more like clay.
Clay particles are the smallest, with a diameter of less than 0.002 mm. They are made from various minerals, many of which have surface electrical charges. Most of these charges are negative, and so clay particles tend to attract positively-charged ions (cations). Positively-charged ions in the soil include many of the plant nutrients we have already encountered, and they are far less
Seed trays, modules and pots
When plants are grown in the soil they can send out roots, make friends with fungi, and source their own nutrients from their surroundings. In gardens we help them do this by improving and feeding the soil, a topic I will be returning to in chapter four. But when they’re confined in containers plants have a limited volume of soil and therefore a limited amount of nutrients to tap into.
An ideal seed compost is able to retain water, whilst at the same time letting excess water drain away to provide an environment that is damp but not waterlogged. It allows penetration of plant roots and is able to anchor plants, but has space for air. Its texture is consistent, and it is free from pests, diseases and weeds that would compete with the seedlings. As we have seen, it doesn’t need to contain many nutrients if seedlings are going to be pricked out; seedlings growing in modules will either need enough nutrients in the compost to support them through their first weeks of life, or suitable supplementary feeding.
There is a big trend at the moment in recycling containers to use in the garden (we’ve already touched on it with recycled food containers used for raising seedlings). There is also a large range of containers you can buy – from cheap plastic pots right through to enormous designer urns. What you choose is as much down to your budget as it is to your tastes, but all containers need to hold a suitable volume of potting compost and retain water whilst allowing any excess to drain away. If you are recycling containers to use for food plants then be sure that they’re clean and that they weren’t used to store anything toxic in their previous life. And remember that not all plastics are UV stable – some degrade when they’re exposed to sunlight.
When a seed sends out its first shoot and it rises above the soil level, germination is over and seedling development has begun. This is a particularly vulnerable time for the plant – it is running out of stored resources and needs to start collecting its own food. In this period of rapid growth it is also particularly at risk from pests and diseases.
When I set about blogging The Peat-Free Diet it was an experiment, an journey into the unknown. My aim was to provide gardeners who want to garden without the use of peat with the information they need to do so, and the book evolved into a gardening primer that assumed peat was not on the menu. My love of science made more of an appearance than I had anticipated and there are plenty of big words to cope with, but it is my hope that they are presented in such a way that they are not hard to swallow.
Potting on
The Pantry contains information about some of the items that are useful for a peat-free gardener, and gardening terms you may come across on your peat-free travels.
One of the big differences between now and the time before gardeners relied so much on peat-based composts is the rise in container growing. An army of modern amateur gardeners has to put up with small gardens, and possibly with no soil at all. Growing plants in containers allows us to garden wherever we like, and even to grow plants that would not thrive in our soil. Some plants are grown in containers to keep them under control; others so that they can be moved indoors in winter to ensure their survival.
Buying plants
There are no diseases that particularly single out plants grown in containers, with the exception of damping off – the fungal disease that affects seedlings, which we met in Chapter 2. As long as plants are kept well-watered and suitably fed (i.e. not stressed) then container culture should be very healthy, particularly if your potting compost was a sterile mix.
Sowing seeds is often the first gardening task of the year, and a favoured way of propagating plants because it’s very cost-effective. It’s the first stage in many plants’ lives and seeds want to grow, it’s their reason for being. And yet some gardeners are intimidated by seed sowing and avoid it where possible and others struggle to grow plants from seed successfully in peat-free compost. So I’m going to begin The Peat-Free Diet with a look at what happens when we sow seeds, the best way to go about it, and how to achieve a good success rate.