As you probably know by now, I'm a huge fan of growing vegetables all year round. In fact, I think that you can winter-sow most of them. You can do the sowing outside in pallet collars or pots for example. It doesn't matter if the soil thaws and freezes a few times over before the seeds germinate in spring. So, what are the advantages of winter-sowing? Well for one, you don't have to fit all the plants inside. Also, the seeds manage really well on their own and the plants grow large and hardy when you do a winter-sowing.

I usually winter-sow leafy greens, cabbage, onion, spices, and a few flower varieties. But what about winter-sowing tomatoes? They are more sensitive after all. But I know that most of us want to have plenty of tomato plants, and they take up a lot of space if you grow them indoors. Would I be able to winter-sow tomatoes successfully?

The bush tomatoes self-seed outside.

How to winter-sow tomatoes

I have actually tried to winter-sow tomatoes twice before. I noticed some tomato seeds germinating in my compost and was intrigued. It must work! So, I tried doing it in a more controlled environment too and sowed the tomato seeds in my polytunnel. The seeds germinated in March and froze shortly after. Last year, I tried it again. I sowed the seeds later though (March). The seeds germinated. And were again ruined in a cold spell not long after. So frustrating!

These past two years, I have also been digging up little self-seeded bush tomatoes outside in early summer and planted them in pots instead. This doesn't really count as winter-sowing tomatoes of course, but they might as well have been. The seeds were after all staying in the soil through fall, winter, and spring. I planted the bush tomatoes in pots in my polytunnel and my results have been great so far!

The difference between my attempts and the self-seeded bush tomatoes is mainly about the location. I decided to winter-sow tomatoes in my polytunnel, but the bush tomatoes came from my beds outside. The difference is actually huge! My polytunnel can get warm even in winter, perhaps 70 degrees (around 20 degrees Celsius) in February. When this happens, the seeds can, of course, start to germinate. But the polytunnel doesn't protect the seeds against frosty nights in early spring. And a lot of plants don't make it. Of course, tomatoes can be sensitive to the cold.

More about tomatoes: Tomatoes from sowing to harvest

We brought the self-seeded bush tomatoes inside and put them in pots.

I let these plants stay in their pots the entire season. I just put the trough on one of my beds between a few other plants in my polytunnel, and they got their nutrients and water through the little holes in the bottom of the trough.

Winter-sow tomatoes outdoors

When the tomatoes self-seed in the beds or in the compost, for example, they germinate at exactly the right time and grow nicely. However, some of them can, of course, germinate at the wrong time. The frost will be the end of these seeds. When the seeds germinate might depend on the variety of course, but I believe it's more random than that. I think that other factors matter more, for example, how deep the seeds were buried and how tall the bed is.

So, if I winter-sow tomatoes in my greenhouse and let the plants grow somewhere warm with sudden cold spells, I most likely won't get any tomatoes. But if I, on the other hand, use the self-seeded plants from my garden or try to sow my seeds in a similar fashion, I will get a very late harvest and the plants probably won't even develop in time to bolt.

What should I do?

Well, I decided to go for a compromise. I'm winter-sowing tomatoes outside and in a plastic crate. I can do the sowing outside whenever I want to, but the plastic crate will have to wait until mid-March. I'm doing the late sowing simply to avoid the issue of early germination and then freezing of course. So, the main difference between this and my previous attempts is that I'm going to do them both outside and later than before.

Of course, I'm also going to sow some plants indoors as a backup plan.

Read more: How to grow tomatoes outdoors

This is what the self-seeded plant looked like in my polytunnel! The top picture shows the tomatoes I got from it.

What's the trend?

Winter-sowing is really popular in countries with cold winters, for example, Canada. I know that plenty of Canadian gardeners winter-sow tomatoes in little cultivation boxes outside. You can use anything from see-through buckets to plastic milk containers. Just drill a few ventilation holes in them.

A lot of people winter-sow tomatoes in the second half of March and some say that winter-sown tomatoes can have a slow start but then grow quickly as soon as you replant them.

Of course, some of the seeds might not germinate at all. This is something that happens with all winter-sowing though. Not just tomatoes.

Read more: How to ripen tomatoes indoors

In conclusion:

When all is said and done, it's really hard to know exactly how a winter-sowing of tomatoes is going to turn out. You do however need to remember that the tomatoes might need some special treatment, compared to other winter-sown vegetables. I'm guessing that it would be really convenient to grow plenty of tomato plants outside so that I can save the indoor space. I do after all get quite a lot of plants on my window sill in spring.

• Tomato seeds do just fine in cold soil throughout winter and germinate when the soil and air temperature are right.
• If the seeds germinate too early, they will most likely freeze if you grow them in an environment with fluctuating temperatures.
• Choose a spot with a stable temperature, this will keep the seeds from germinating too soon.
• You might need to let some of the late plants keep growing in the greenhouse, otherwise, they might not be able to give you a harvest before it gets too cold in fall.

I do need to highlight the fact that the self-seeded tomatoes are bush tomatoes. These are low-growing tomatoes that you can harvest sooner than the taller varieties. I haven't decided which varieties I'm going to use this winter, but I'm guessing it will be both.

Do you have any tips on how to winter-sow tomatoes?
/Sara Bäckmo