When we came to Finland I immediately started building a small tomato green house. I built it from old cupboard parts, basically with nearly no costs at all - just for the screws and the PVC foil. The green house served very well for my purposes but I lost 2 of the 4 plants from then to now. What has happened? We built this tomato house like a raised bed, with a mixture of small and medium branches on the top floor, leaves above it and then a mixture of soil from the garden with some kind of compost soil. For the first week everything seemed fine. Then the temperature suddenly dropped and the first plant just went into limbo, and never recovered. It was the one plant in the front, most exposed to the cold.
So the other 3 tomato plants were just fine until, yes, until the ants attacked. Somehow within 5 weeks after starting this tomato house the soil was full of ants. We haven't had any clue why that happened, so we read through a lot of literature for instructions howto get rid of ants in a organic / biological way. We already had basil as a companion plant but now we planted onions inbetween; which didn't help. Another book stated that ants don't like lavender. Luckily we had some in the garden so we put some lavender between it. Didn't quit help, even though I thought the numbers of visible ants were reduced. But that was probably just an subjective impression, there were still a lots of it. From the start to 7 weeks after another plant went down.
Problem solved, lets grow
Then we used soda and suddenly the ants were gone, all of them. And from now on the tomatoes just grew. From now and then I put some liquid nettle manure on the soil and removed some suckers. Of course we didn't forget to water the plants, but that's basically it. Now winter is coming and frost is already upon us. This week the second to last went down a natural death. A fungi got onto it. The last standing still has two nearly ripe tomatoes on it. Let's hope we get them ready.