Seed germination

NormandyLiz · February 2023

Is there anywhere you can get more accurate guidance on seed germination requirements? I usually follow the instructions on packets but they are often very vague. 'Sow in March' could mean anywhere from 1st to 31st, regardless of the weather.

Some seed merchants are very good and give temperature guidelines but most don't. As well as temperatures, I'm assuming that cloud cover would also impact the amount of daylight.

Question 1 is therefore how do you go about determining the optimum time for sowing seeds?

Question 2 is 'under glass'. I don't (currently) have a greenhouse but do have a plastic sort of cold frame. It clearly doesn't provide the protection of a proper greenhouse but does keep frosts off. Would using this change the timing of sowing or would you follow 'sow outdoors' timings?

Fairygirl · February 2023

It can be trail and error with many seeds. The important thing is what conditions you have once they've germinated, are growing on, and then need moved up into pots.
Anything plastic will only keep wet stuff off, it won't really provide protection from frost, so those types of cold frame or growhouse are fine for hardening off, and protecting from rain/sleet/snow/wind, or sowing hardy annuals, but again - the timing matters for getting them outdoors - that's the main factor. It's why I don't really sow before March, and even then, they're started in the house. It's still too unpredictable for putting small plants out in April here, so I aim for May to get hardy plants outside. Those are mainly sweet peas.
The less hardy types will be sown end of March and would go out later in May, or early June, as long as they're looking tough enough. I often sow stuff in April too, which can be easier, but that's mainly follow up salad crops - lettuce, mizuna, basil etc. Basil has to stay inside until much later anyway.

Some seed will be fine in early March in your frame if your climate is generally going to be warm enough for them to germinate and grow. If in doubt, sow some, then wait a few weeks and do more. Keep a note of how they do, and also a note of how the weather's been.
Some seed will need a period of cold to set them off too, so it does depend on what you're growing.

Buttercupdays · February 2023

For probably the majority of seeds the best time is likely to fall somewhere between mid March and the end of April for indoor sowing.This allows time for plants to grow strong enough to be planted out from the end of May. For biennials sowing is a bit later around May- June. This should give enough light and heat for hardy plants, but those from warmer climes may need additional help.

For any given year however there is always an element of luck, given our changeable weather, now additionally affected by the uncertainties of climate change. Last year for instance, May gave us lovely day times, followed by sharp frosts overnight that killed off things in my GH that had survived all the winter months!

I hedge my bets by starting things off indoors in a heated propagator, then moving them on quickly, if hardy like sweet peas to an unheated one, then a bright window sill, then my now unheated GH. Some plants need longer germination times or grow more slowly, so may get planted earlier or stay in the propagator longer. I'm sowing aubergines today, but my windowsill already has some chillies, artichokes and parsley that I started earlier and some other seeds that I was 'testing for viability'. Some came good

All available windowsills get requisitioned as the days progress to give all my plants the best possible chance of a good start, but even after many years of gardening I still get it wrong sometimes.

Fairygirl · February 2023

I do too @Buttercupdays, but I think one of the biggest mistakes made with seed sowing is the amount sown. We see it every year on the forum- people with no room for the pots they've moved seedlings into, and then they don't know what to do as it isn't suitable to move them outside.
I grow fewer seeds than I used to, as I simply don't have the room indoors, and the little growhouse isn't warm enough to move most of them into until late April or early May. It's also why I grow very few half hardy plants. The new dahlias will be inside for quite a while too

NormandyLiz · February 2023

Thanks both.

I'm assuming others have the same problem as me - very limited options on where to put pots. Our house has almost no windowsills, I don't have a greenhouse, but I love growing from seed. Seeing those first leaves emerging is magical.

It's fortunate that so often packets have more seeds than you think you'd need, so at least the trial and error, with plenty of error, isn't the end of the world. We're due a colder period next week, but I'll pop some of the hardier ones in after that passes and see what happens. And keep a diary, not something I'm good at but it is sound advice, thanks @Fairygirl.

On the plus side, the astrantia I sowed at the beginning of winter have all germinated. They're now in the growhouse but having read the above I'll pop them on the only window ledge when it's cold next week. They're too precious to loose.

Fairygirl · February 2023

If your astrantias have survived so far, they should probably be fine. They're hardy perennials.
It can sometimes be counter productive to cosset them after they've been in harder conditions. If they're a decent size, I'd be a bit wary of bringing them into a much warmer site.

NormandyLiz · February 2023

Okey doke. I'll leave them out in the growhouse. They're still tiny, no true leaves, and I would be gutted if they fail but I do have more seeds in the freezer - I thought I'd try both methods to double my chances!

Fairygirl · February 2023

Ah - if they have no true leaves, it's possibly not ideal out there for them then. The seed leaves are only the start, so if the conditions aren't good you might not get any true leaves at all.
If you have several pots or trays, you could always leave some and bring some in. That's the best way to see what suits your conditions.

bédé · February 2023

Your time and timiing is a factor. As is the temperature. Don't worry too much, sow little and often, and in different places. You will gain experience.

NormandyLiz · February 2023

and ps - I'm not sure many would agree that coming into our house would classify as 'cossetting'

. The theromostat is set at 14°C, 12° overnight.

Fairygirl · February 2023

'bout the same as mine then @NormandyLiz

The only time my [south facing] kitchen has been above 15 since last year was when there was some sun last week, and it got to 18 in there for a while!

Seed germination

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