I’ve sourced 27 varieties that I hope will be adapted to our cooler summers (I will be growing outdoors). I would also be super grateful if anyone could share any seed with me that is already diverse/cold-adapted. I anticipate that the greatest issue will be fruit maturity and achieving proper sweetness due to lower sunlight intensity.
I would also appreciate any advice on sowing and planting dates, as I’ve never grown watermelons before. I am interested by your experiments of planting at different stages, Thomas, and was already planning to sow a bit later and plant out young - I have always found cucurbits to prefer this over sitting in pots, so it’s good to know you have experienced the same with watermelons specifically. I think for this year I will not sow direct, as it feels too high stakes (and I’m growing on a clay-heavy site). Eventually, I hope to achieve direct sowing, but I think that may be a couple years down the line.
Looking forward to hearing about everyone’s experiences!
I haven’t found sweetness to be problem and I grow in a much cooler climate. First year when I had little more varieties, there was very wet and fairly cool july when fruits were ripening and the few varieties that had started making fruits before that had good fruits. Flowering effectively stopped for few weeks so it really was having effect on them. Problem what people might have is that they aren’t as patient to wait 45-50 days for them to ripen, when in warmer climates that might be 35 days. Second problem is just having the wrong varieties, which might be the reason that some can’t make most of the little warmth they get.
The biggest problem you will have is early season cool and rainy weather. You might be able to escape that by sowing mid june. That should give you the necessary 90 days of decent weather for fruits to ripen. To me that sounds like the most appropriate window. You don’t have that much need to push for cold tolerance early in the season like I when you already have enough time. If you have good weather you could sow a little earlier, but I wouldn’t go earlier than early june. I have had warm starts to the year and then mid june rain with lows going down +5 and below which caused most of the seedlings to start to “melt”. Luckily that year that wasn’t much more than a week and temperatures bounced back. Some were unaffected by that, but last year had even worse and barely managed to salvage 2 plants with protection.
I prefer direct sowing, but if you need to make most of the little seeds you have I would use 6cm pots and transplant them before the first true leaf starts to grow. So about 10days old. That stage they don’t seem to be that affected by transplant shock if they have been just grown fairly smilar conditions like greenhouse. If you have a windowsill or something similar, then I don’t see the advantage. About the same sowing time.
This is useful to know - I’m glad to hear you haven’t had a problem with sweetness. Interesting about the cool/wet period affecting flowering more than already-formed fruits. That’s good to know. Do you have a list of the best varieties you found for cooler climates? I suspect I have most of them already, but it might be useful to have in the public record in any event, if you have a list readily available?
This is interesting, thanks for your thoughts on this. One benefit of being in London is it’s a couple of degrees warmer than the rest of the country on account of the ‘heat island’ effect. I might trial a couple different sowing dates this year, to try and gather some useful data - maybe I will try some in pots and then direct sow some more a couple weeks later. Thanks again for all the info - it’s incredibly useful.
I don’t have any really good comparisons. First year that I grew more varieties (I think about 6-7 watermelons) was the only cooler summer overall when I had staple varieties. Then blacktail mountain and Janosik did the best, with early moonbeam being just a little slower. Others were just slow enough that flowering didn’t start before cooler period started and then they didn’t have time. Those failed varieties were mostly russian and 1-2 from north america that I can’t remember name of. Next summer was record hot so there wasn’t really that much difference in earliness. Something like a week, which ofcourse might be decisive, but since they were from transplants those differences can come coincidentally from transplant shock etc. Also I selected varieties very carefully based on recommendations to northern climate. What I had besides those above that produced (and that I remember) were: sweet siberian, cream of saskatchewan and golden midget. There were some others that I can’t remember the name of which maybe didn’t do the best. The next year I also direct sowed mini love and it was that year (again hot summer) week later than the best from my then F2/F3 mix. That year I also used cloth early in the season so maybe there might have been more differences considering how much difference removing it made the next year.
Best way to learn is to make mistakes and the more you try the more you expose you to mistakes. I would just caution not to get carried away, especially the next years when you have experience from one year, but not the whole picture of the range of year to year variation. I would say it’s saver to sow them when it’s cool, but late enough in the season rather than when it’s warm/hot. If the ground has warmed up enough, they can emerge in 5 days. Just fast enough to be exposed to sudden change in weather. If the ground is cool and weather not that favourable lets say early june, they can take 2-3 weeks to emerge. So they are more likely to come once the weather is likely to remain good.
Also now the first year you better play it save. The seedlings can have high mortality in cool weather and I would rather take my changes with them having enough time to ripen fruits rather than exposing them to high selection. Like I said, last year I had 2 survive out of thousands of seeds sown and the year before it was few %. So try to get as many seeds and play little bumblebee to increase crossing to get as big varied mix for the next year.
The problem in comparing different regions is that there are so many factors more than just average temperature. Like if you have 15C during the whole day with 24h sunlight is different than having same 15C average, but with high of 25C and low of 5C with 10 hours of night. Overall the latter might be worse for most sensitive plants. So even if the recommended temperature might be too “easy”, what they can survive in other regions might not work for you either. Another thing is also how much variation there is. I’m a little bit of weather nerd and so I have researced weather conditions around the world. In some parts of the continental US record high for february is 27C and record low -27C. Now the variation probably aren’t that much in France or many other locations, but there is always maybe more than we would hope as gardeners. So it might be necessary to wait a little more until the range of variation is more tolerable. At the same time, if you want to have selection pressure you need to risk it little every year. Shit loads of seeds makes it little more likely that something will survive. I did look at the weather history around your area and it looks just as much of a conundrum early in the season as summers here for watermelon. Some mays looked just as shitty as last june here. I don’t think it’s impossible to breed them to tolerate that kind of conditions even if it might be uphill battle. If you look at cucumber, it originates also from a lot warmer region and has been adapted to even the coldest regions. It must have had the benefit of coming from mountainous region and so there have been good changes to incrementally improve it when you need to move only short distance to have little cooler climate, yet relatively long seasons.
Let’s bring back the topic to its core : 2026 watermelon growing season.
I’m gonna be direct seeding within a week or so - along with melon, maxima and moschata - :
I have my main population: resowing the best and earliest of 2025 in priority, discarding about 3/4 of last year. Something like 300 plants. Direct sown, plastic tarp, no irrigation, with some early vigor selection by sowing more than needed, with spacing, and discarding the slowest at a month post sowing.
and an alongside project of trying to fix a “moon and star … and stripes” trait of an overwhelming watermelon of last year, overwhelming both from an aesthetical and taste standpoints. Seeds sown in trays already. Waiting for the first real leaf to show up as it’s gonna be giving me cues of the “moon and star” trait - the “stripes” trait will show up when fruiting, so I may self these before seeing it showing up - or not showing up !- on fruits.
Biggest risk is sowing when it’s hot for the time of the year and changes to more normal/to the other extreme. I think it’s better to sow when it’s cold. Then they are still save under ground, but can start to develop. Based on forecasts it might even be good time to sow there now in the next few days as the cooler weather is supposed to turn warm at the turn of the month. Maybe little risky for squash that can germinate faster, but melons and watermelons probably will take at least 10 days to emerge if average temperatures are under 15C. Ofcourse it might turn cold in may also, but it might also go directly to fullblown summer and you loose the change to make cold selection. Maybe ideal would be sow when it’s still cold, but the forecast shows warmer weather in a week. Then it’s quite certain that you get some cold germination selection, but it’s also quite ceetain to warm up to move you towards more save time of the year. My situation is so much easier when there really isn’t time to wait. I might get cold selection or might not. Although I still use similar approach, just shorter window to make my move.
I personally have no longer the mind bandwidth to go into such considerations. Next fall maybe… The die is cast there: time to sow. I was willing to sow couple days ago but couldn’t due to tractor unavailability.
It’s probably not going to make difference most years and that date seems quite good, right on the edge. In your case you can always resow if you have a bad year or if you have couple survivors like I last year, you still have time no matter how much they are set back. But if I have learned something in the last few years is not to get complacent. Better not to have set dates or go even earlier just because last few years have been fairly easy. Hope for the best and expect the worst. Last year I came to realize that the germination can be so uneven that at the right moment the fastest might emerge and then be killed by cold weather, but the slowest might emerge late enough that they are saved by the next warm spell. And so you have plants that in terms of cold tolerance are the worst. I know I might overthink it sometimes, partly because of my climate I have to be precise.
I’ve re-red your post :
There is no real risk of frost here from 1st April on. So sowing now I would expect zero loss post germination, and so a correct selection relative to cold soil emergence. Less risky there and now.
From my experience melons and watermelons die with a lot less than frost. Hard to say exactly what’s the limit, but rain seems to make it worse. Average temperature of under 15C for long seems to be limit for most early in the season. Shorter periods like 2024 only like 98% died when it was week under 15C average, between 11-14C average with 16-19C highs and ground level little over/under 5C. I suppose that was quite fine as some were unaffected by it, but can’t be that far from the limit. And it might be different there when you have little longer nights. Last year was about the same range, but it seems like it had more effect. Possibly because there was more rain (50mm in few days) or because the spring was cooler and so it got cooler faster. Really hard to say how it might be there. Warmer winter and spring might make the cold spells more tolerable, but on the other hand the night might affect more. I didn’t mean that you could or should make big changes to your sowings, but some cases there might come situations where they will come up immediately if sown and then have longer exposure to possible cold weather. But it would really be only if there has been unusually hot period that is expected to turn cold in a week. Or if it’s really cool, may´be there isn’t such a rush to show right away, but at least see if there seems to be change coming. So quite specific, but still it seems to happen more and more at least here. Sowing when it’s cool might be saver option if it seems to be in forecast. In too cool the germination might be bad, but last year did show that it still isn’t zero. You will probably know more in few years. At least it would be good that there were some challenges.