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.
Producing seeds is one way that flowering plants reproduce themselves. Each seed is a survival pod, containing everything a new plant needs to take root and grow – with the baby plant itself held in suspended animation.
If the seed lands up somewhere where conditions are favourable, then it will germinate and start to grow. To do so, it needs three things. The first is water – seeds are dry and need to take in considerable amounts of water to spring into life. The second is a suitable temperature, which varies greatly according to the plant species. And the third is oxygen – plants breathe (respire) just like we do. Without sufficient oxygen they can’t use the resources present in the seed, and they can’t grow.
Germination is the process whereby a seed springs into life, and the first stage in germination is called imbibition. You don’t need to remember the word, but this is where the seed takes in water. It swells and the seed coat cracks, allowing more water to get inside to the baby plant (the embryo).
Unless you’re soaking seeds in a jar of water then you won’t see the first stage happening. The second stage is usually hidden from view too, as the next thing to happen is that the first root (the radicle) appears. Roots anchor the plant into the growing medium, and allow it to draw up water and minerals from the soil. They head downwards, away from the light.
The first visible stage of germination is the final one, when the first shoot (the plumule) emerges from the soil. Once the stem starts to grow, and the seed leaves unfurl, then germination is over and we’re into seedling development.
The key thing to note about germination is that – apart from water and oxygen – the seed is relying on its own resources. They’re kept in the cotyledons (which often emerge as seed leaves) and the endosperm if it’s present in the seed. The seed doesn’t need any external nutrients at this early stage.
In a natural environment each seed is sent out into the unknown. It may simply drop to the floor, or be distributed by birds or the wind. It may even float away. If it were to germinate in the wrong place, or at the wrong time, then it wouldn’t stand a good chance of survival – and so many seeds have specific requirements to break their dormancy and bring the embryo out of suspended animation.
Cultivated varieties of plants have often had these dormancy requirements bred out of them, and merely require the triad of a suitable temperature, moisture level and oxygen supply to germinate. But if you grow more unusual plants, or save seed from less cultivated species, then you may run into some interesting requirements.
For example, there are plenty of seeds that need to experience a period of cold before they will germinate. You can try to mimic this cold stratification by sowing seeds into damp compost and popping them in the fridge for a couple of months, but if you live in a suitable climate then the ideal low-effort way is simply to sow them in autumn and let winter do the work for you.
There are also seeds that require periods of heat, and those (like many sweet peas) that have such tough seed coats that they need to be damaged (it’s called scarification, but not because it’s scary trying to damage the seed coat without damaging the contents!). Some seeds even need to be exposed to fire or smoke – that’s because they stand the best chance of having room to grow, and access to the nutrients they need, if they germinate when fire has culled the local vegetation.
Seed coats can also contain chemicals that inhibit germination; a thorough soaking with rain is what they’re waiting for. Some seeds only germinate in the light, so they know they’re not in the shade of a larger plant. And some only germinate in the dark. And there are still others for whom staggered germination is the order of the day – they hedge their bets by germinating seemingly at random over a long period of time, in the hope that some of the seedlings will survive.
When you’re sowing commercial seeds then it’s important to check the packet to see whether your seeds have any special requirements for successful germination. If you have problems germinating seeds for which you don’t have the instructions, then a quick check online (or in a reference book) will tell you whether they should have germinated under the conditions you gave them.
There is another factor that affects a seed’s ability to germinate – and that’s its viability.
In the next post I will talk about seed viability. From there my intention is to cover the basics of good seed sowing, more advanced techniques and seed composts. If you have any thoughts about what you’d like to read in the book, or comments on what you’ve read so far, then do let me know.