Seed sowing, and then what?

I mentioned on Saturday that I’d sowed a lot of seeds this year. It may be of interest to some what I do with them if they germinate successfully.

I use Sylvagrow compost for both seed sowing and growing on. It is supposed to have a base level of feed in it, but it is surely not very much. Seeds that are quick to germinate grow fine for a short while then get pricked off into fresh compost. Seeds that are slow to germinate, or slow growing seedlings, will need to be liquid fed or they will not grow very much at all.

I sow most seeds in 9cm pots, pricking them off when they are at risk of being difficult to tease apart. In most cases, I prick them off into cell trays. I use 20 hole trays that are half the size of a standard seed tray. I find that if handled carefully I can get six to ten seasons out of them before they fall apart. Again, anything in the cell trays for more than a couple of weeks will need liquid feeding to keep it growing.


Sometimes I can fill a cell tray, tap it firmly to settle the compost, then using a pencil as a dibber, make a hole and feed the seedling roots into it. Sometimes the roots are too big and I effectively pot each plantlet separately into a cell.

Some seeds I sow directly into the cell trays, especially somewhat larger seeds like Morning Glory, Tagetes, Beetroot and spring onions. Big seeds like beans and courgettes I sow directly into 9cm pots.

Some things get planted out from the cell trays. Lettuce, beetroot, onions are examples. I find with the veg that the really vulnerable stage as far as my allotment is concerned is the period until the young plants are about an inch or two high. I don’t get many losses from cell grown plants, even if they’re quite small when planted.


Most things get potted on from cell trays into 9cm pots. The flower garden affords far more hiding places for slugs so I like to put out a somewhat larger plant in the hope it will survive better. It also means I can sow earlier and keep the plants growing in the greenhouse while it is still liable to be cold, even frosty outside. It will vary but many of these plants will be in the 9cm pots for four to six weeks so I use controlled release fertilizer pellets mixed into the compost to provide them with adequate nutrition. I bought a 25kg bag of Osmocote Exact 8-9 month granules last year and will get at least three season’s worth of potting from it, provided I can keep it in good condition. It is indoors, sealed tightly in its own bag, inside a bin bag. I generally mix 40 grams in 10 litres of Sylvagrow compost. You can get smaller quantities of it on eBay, where people have bought 25kg and broken it down into smaller amounts.

Once the plants are well established in the pots they get moved outdoors to harden off. I have carrying trays for the 9cm pots so moving them into the greenhouse if the weather is frosty or excessively wet or windy is fairly easy. Finding room is usually less easy. After a suitable period of hardening off they get planted in their final quarters.

16 thoughts on “Seed sowing, and then what?

    1. I think a lot of seedlings put down a deep root to get them into reliably moist territory, then set about producing laterals. With trees and shrubs I’d usually snip them, less often with annuals and perennials. Camellia seedlings just go straight out of the holes in the bottom of the pot, or round and round.

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  1. Thank you for a very informative post. It’s good to learn how things should be done. My method skips the cell tray stage….and I’m not so generous with the nutrients, but then again I’m not as successful with my seedlings as you are! I will try and grow the next batch in stages as you suggest and let you know how they go.

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    1. It’s mainly lack of space makes me reluctant to put things in bigger pots sooner. I have more time than space. In nursery days it would have been the other way round and I’ve have done things a little differently.

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  2. Good information. I am struggling to find decent compost here and I can see that yours is just what I was thinking about at lunch today, when wondering why I was no longer successful with seedlings.

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    1. One of the greatest strengths of peat was its consistency. As it slowly disappears there seem to be a lot of products offered which don’t tell you what’s in them, which always makes me a bit suspicious. What do they have to hide? essentially. Green waste is an ingredient which seems to me fraught with difficulty in that I cannot see how you could ever be sure what had gone into it, be that broken glass, hormone weedkillers, nutrients, mineral content or whatever. I have used potting compost with 10% green waste mixed with the Sylvafibre base and it was OK but no improvement on the compost without it and inclined to stand too wet in winter. To a considerable extent it’s a question of how well you understand the specific qualities of a particular compost and adjust your husbandry to get the best from it.

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      1. Agree 100%. I am having a lot of compost difficulties here in France. I use JI 2 that my husband brings from England. I did lots of research last year on peat-free for a gardening column that I write in an English/French monthly paper. It was so frustrating. I ended with a shortlist of about 6 possibles, none of which are sold in local outlets, some now discontinued, others which actually do include peat, although in small quantities. We just don’t have the choice that you have in the UK. Your post was fascinating – could just see from the roots and consistency that the SylvaGrow would be one to try. Perhaps after the lockdown is over and my husband goes back to work in England I shall have to ask him to import the SylvaGrow and give it a try. What I do know is that what I’m doing at the moment ain’t working!

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      2. Melcourt, who make Sylvagrow, are the main large scale suppliers of peat free composts to commercial growers, in my nursery days we were early adopters and I used around 200 cubic metres of the stuff each year over a range of a couple of thousand varieties of plants. It’s not quite as easy to manage as peat, mainly because the surface dries out when there’s moisture underneath so you can’t tell just by looking if the plant needs watering, but with experience it will grow most things as well as peat and some things better. No, I don’t have shares in the company, perhaps I should.

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      3. Ha! The drying out problem is perhaps why I should use it – I have a tendency to over-water (which I try to curb!) and plants in JI do not like it! Thanks for all your wonderful information!

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    1. The CRF pellets are used almost universally by nurseries but have to be mixed just before the compost is used so are never in retail composts. Given moisture and adequate temperature they release nutrients and if there is no plant to take them up or irrigation to wash them away, they build to phytotoxic levels in a few weeks.

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  3. I didn’t get a single germination from my dahlia seed. Who knows why! But good to see yours growing away so strongly. It’s always good to see how others so seeds. Some seeds I cover with old compost bags cut up, some go under the propagator lid. I am sure I knew once why I do that but I’ve long since forgotten. 🙂 When to start sowing is my dilemma, but I’m getting used tot the potting shed temperatures now and things,other than dahlias, are going well. Two dwarf beans are down due to slug attack. They lurk everywhere.

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    1. Very odd about the Dahlias, I reckon to get very high percentages with them. People cover seeds to keep the compost surface moist mainly, but of course some things needs light to germinate and if sun falls on covered pots it can get very hot underneath. Pitfalls everywhere, and slugs.

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