It usually amazes me when someone asks what I think is a dumb question about growing plants from seed. I’m afraid I tend to forget that I’ve been doing it for 30 years or so and much of it is second nature. For newbies, growing from seed is, well….new. Totally.
So here’s some of my experiences. I hope you find them useful.
Most books will tell you to buy a bag of commercial seed-raising mix, put it in a pot, sprinkle the seed over the top, cover with a depth of mix equal to the thickness of the seed and water gently.
When the seedlings germinate (they never fail to do so in the books—real life is often quite different!), you ‘prick’ them out into larger pots to grow on. They always tell you to do this when the first set of true leaves appear. (Note: the first set of leaves to open from a germinating seed are the seed leaves or cotyledons. They are often very different in size and shape from the true leaves which appear next.)
Seedling with cotyledons and true leaves:
After that (say the books), you simply water the seedlings, perhaps add a little fertiliser and wait for them to grow big enough to plant out in their final position.
That’s all right as far as it goes, but seeds vary enormously. Here’s a few examples:
On the left is tiny, tiny seed (like dust) of camomile; then tomato, then peas and finally broad beans. It’s generally accepted that you sow large seed, like peas and beans, direct into the ground, bypassing the potting on stage. The disturbance to growth that would result from trying to pot on a large bean seedling (if you could do it without breaking the root) would set the plant’s growth back too much. Yet I still see punnets of pea and even bean seedlings for sale in nurseries and Sunday markets. Don’t buy them.
On the other hand, tiny seed means an equally tiny seedling with equally delicate roots. That means trying to prick out something very small with a very large thumb and finger, while trying to avoid crushing the poor thing to death.
So one of my tricks for tiny seed is to sprinkle a pinch of seed onto the surface of a small pot and allow all to germinate, then thinning later to the strongest seedling (often nature will do this for you by simply wiping out the weakies). Be careful though, that the little group of seedlings don’t succumb to fungus that will wipe them all out. Good air circulation around them is important. The plant is allowed to grow on in the original pot, bypassing the pricking-out stage and can be put in the ground without too much transplanting shock. If you know your plants and their growth habit, sometimes it’s possible to leave 2 or 3 seedlings to grow on and plant out as a group. You wouldn’t do this for a large tree, but you might do it for an annual or perennial, where a group of 2 or more plants will grow successfully together.
This doesn’t mean that all tiny seed should be treated in this way. Some small seeds resent the disturbance of potting up and planting out and need to be direct sown. Carrots are an example (and parsnips, although their seed isn’t as small). They must be direct sown and thinned in the ground. Thinning should take place as early as possible, but sometimes I’ve been able to get away with a succession of late thinnings and get a feed of baby carrots into the bargain. It’s possible to buy carrot seed sealed at nice regular intervals in a ‘seed tape’, which means thinning isn’t necessary:
When sowing seed, you don’t need a deep pot; this is only wasteful of seed-raising mix. A shallow punnet will do. A margarine container is suitable, but even then that can be a bit deep. I’ve taken to using those black plastic trays that supermarket meat comes in. A few holes in the bottom for drainage is all that’s needed:
Don’t forget to label with the name of the species and the date. Now, not later. Memory doesn’t recognise ‘later’. And keeping written records is most important if and when you want to check back on germination times (for forward planning, for example).
Once your seeds have germinated, forget about potting on at the first true leaf stage. They’re mostly still too small to be handled. Wait till they’re a decent size and have a small cluster of roots. You might need to do some experimental poking about at this stage. Some seeds make good top growth and very little root growth. Others make a lot of roots and still look pretty peaky on top.
While they’re waiting to be potted up they will relish a dose of weak liquid fertiliser—diluted worm juice is good, if you have a worm farm. If you’re going to use pelleted fertiliser, make sure that no pellets are sitting right against the seedling’s tender stem. The sudden influx of strong chemical can dehydate and kill the seedling.
If you’ve started your seeds off inside then they should be given adequate light as soon as they germinate. Otherwise they stretch up and become leggy and fall over. That usually means outside, although not in really hot sun.
You might start by using a commercial seed-raising mix and then decide to experiment with something else entirely. At various times I’ve used sieved potting mix, a mix of sand & cocopeat or commercial mix. At the moment I’m using a mix of 2 parts perlite:1 part cocopeat. It makes a nice light, but water-holding mix that makes it easy to lever out the seedlings.
I’ve found that the longer I leave them, the stronger they are and the better they transplant. Sometimes I may have to trim a long tap root, but as long as side roots have formed this isn’t usually a problem. If there are strong, multiple side roots sticking out in all directions and you can’t get them into the hole you’ve made without crushing them, then here’s a neat trick. Dip the root system in some water. As you pull it out, the roots clump down into a narrow cylinder, allowing the seedling to be dropped straight into its hole.
When I’m potting up seedlings I fill the pot with potting mix and make a hole with a thin flat stick by working it from side to side. The mix has to be damp for this, otherwise it will fall back into the hole and you won’t have a hole! So I fill my pots and water them overhead with a fine rose spray on the hose and let them drain.
Here’s a selection of some of the pots I might use for potting up seedlings:
The pots don’t need to be very big, otherwise you have to wait too long for the seedling to grow before planting out. I want to get a nice strong seedling into the ground and growing as soon as possible. The tall pot is 50 mm (2″) square and 150 (6″) mm deep. (By the way, that black thing in the cement course between the bricks behind the pot is a plump little spider. See the legs. She’s found a nice warm spot to shelter in).
Tomatoes get special treatment. I want them to be a decent size so I can put them out as soon as the weather warms in spring. I don’t want to be actually sowing seed in spring and planting seedlings in summer. I want them growing and fruiting as soon as possible. So tomatoes get sown inside in late winter, on a heated propagating mat. I soak the seeds overnight, then plant them in cell trays, 3 seeds to a cell. Later, I thin to the strongest seedling. It’s important that they get plenty of light once they’ve germinated, to stop them becoming leggy, so they’re moved right up against the glass window during the day and moved further back into the warm room at night.
Cell trays on the heated propagating mat:
The first batch of tomatoes has already germinated:
When the weather warms enough outside, the cell trays go into the polyhouse until the seedlings are big enough to transplant into their final pots. They get fed really well at this stage and are planted out from these small pots.
Tomato seedlings ready to plant (from last year):
It doesn’t really matter if tomato seedlings get leggy, because they can be planted out right up to the level of the first set of true leaves. New roots will grow all along the stem and make for a much stronger plant.
Here’s a batch of beetroot seedlings I bought at a Sunday Market recently. They’ve been allowed (by the grower, not me) to become a bit leggy and have flopped sideways. You want to try and prevent your seedlings from doing this:
I potted the seedlings on into tall tubes. I didn’t want to plant them straight into the garden as they’re too small, but I wanted to eliminate the legginess, so I’ve potted them right up to the base of the cotyledons:
The tall tubes will allow a good deep root system to develop, but won’t stop the formation of the swollen root. I’ll put them out when they’re bigger and the ground is warmer.
If you’re going to have a go at growing trees and shrubs from seed, you need to know a bit about the plant species and where it grows naturally, especially what the normal germination conditions are. For example, the seeds of many plants from the northern hemisphere drop in autumn and spend the winter buried under snow and won’t germinate until the spring. Being buried under snow is a requirement for germination—they won’t germinate without this happening to break dormancy and prime them for germination.
If there’s no snow handy, you can get around this by ‘stratifying’ the seeds. This means sowing them as normal, then putting the pot or punnet in a plastic bag and storing in the fridge for a few weeks.
Some seeds, e.g. wattles, have a hard seed coat that needs to be broken down to allow moisture to penetrate and start the germination process. In the natural environment, fire usually does this by cracking open the seed coat. To get around this, you can sow the seed, pile some leaves onto the pot (not a plastic one!) and set fire to them, however it’s easier to put the seeds in a cup and pour boiling water over them, then leave them to soak. The ones that swell up can then be planted.
Many plants that come from fire-dependent vegetation areas (Australia and South Africa come to mind) need fire to germinate their seeds, but it’s not only hard-coated seeds that are in this category. In this case it’s chemicals in the smoke that trigger the seeds to germinate. Experimental work in South Africa and later at King’s Park in Perth proved this.
Seeds were treated by enveloping them in smoke from a drum of burning vegetation and germination was improved. In another experiment, the seeds were watered with water that had smoke bubbled through it, with the same result. The water was chemically analysed and a synthetic brew made up. It’s now possible to buy ‘smoke water’ to use on difficult to germinate species. I’ve been using it for some years on Australian natives with great success.
So, germinating seeds can be quite involved, but fortunately for us, growing veggies from seed is pretty easy!