Seed trays, modules and pots
21.08.2023 - 11:58 / theunconventionalgardener.com / Emma Doughty
Seed viability
If you sow a batch of seeds and none of them germinate then it’s easy to imagine that you’ve done something wrong. Perhaps the temperature was too low (or too high), or you didn’t get the watering right. Perhaps the seeds succumbed to a pest or a disease before they even emerged from the soil. All of these are possibilities, but it’s also possible that the seed you sowed was not viable – that it was not capable of germination.
If we think back to the analogy of a seed being a survival pod, with a plant embryo lying dormant inside, then it’s easy to realise that they don’t have an unlimited lifespan. Eventually they will run out of the energy needed to maintain the life-support system, and when that happens the embryo will die. How long this process takes is very much dependent on the plant species, and it’s not a black and white thing; the percentage of viable seed in any given batch drops over time.
Seed packets often come with a Use By or Sow By date for this reason, but you can also find tables of expected seed lifespans on the internet.
It’s also possible that the seed was not viable to begin with. We can’t see what’s inside the seed, but variations in plant health and environmental conditions mean that not every seed that is created and released is alive.
Seed Banks (like the Millennium Seed Bank at Kew, Sussex or the Doomsday vault in Svalbard, Norway) go to great lengths to ensure that the seeds they collect for the future are viable and remain so. Most seeds are what scientists call orthodox, which means that they can be stored for long periods of time at low temperatures if they have been thoroughly (but not completely) dried. Stored seed batches are tested for viability at regular intervals.
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.
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.
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
I used to do a lot of seed swapping, attending (and holding) seed swaps, and doing ad hoc swaps with gardening contacts, many of whom I met online. I used to quite enjoy making homemade seed packets, and did some lovely ones from old botanical illustrations. Understandably this faded into the background over the years that I was without a garden and establishing a new one. I’m also trying to be a lot more restrained in my seed acquisitions, since seeds don’t last forever and I have neither unlimited time nor space in which to grow them. Last year I went to a local seed swap only long enough to give them my excess seeds!
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.