How I Sow and Grow Tomatoes
Like much of my planting, tomato seeds start in a 1/4 size seed tray or similar with a standard seeds mix. The seed tray is filled to around 1/4 from it's rim, and seeds are placed an inch or so apart in the tray. After spraying them down with some water, the seed tray is topped up with more seed mix.
They are then left on a source of heat either on a windows sill, or in the grow tent, covered with a plastic lid to lock in the moisture. If the seedlings were germinated on a windowsill, once germination takes place and the first leaves are developed, I move them into the grow tent, keeping them on a heat mat or heated propagator. The more light they get during this phase, the better. If kept warm, growth can be quite rapid and soon, the seedlings will start to show signs of a second set of leaves. By now, any cover for the seedlings can be removed to prevent dampening off.
As the second set of true leaves become formed, it's time to start thinking about a couple of things. Firstly, potting the seedlings on into their own pots, but also to make sure the seedlings are regularly disturbed. This can with be done by adding a fan into the grow tent to encourage some movement, or occasionally, brushing along the tops of the seedlings with the hand. The purpose of this is to encourage the seedlings to strengthen their main stems.
After around another week of the seedlings putting on more growth, it's time to pot them on into their individual posts. Each seedling is pricked out, and buried suite deeply up the stem of the plant into the pot, This helps the seedlings become stronger, and also build a better root system as new roots will be developed direct from the stem which is now buried in compost. They are kept on heat and under light for a while longer. It might become the case that at some point, they grow too big for their current pots. If that is the case, and the weather is not yet good enough for them to be put outside under cover, they may need potting on one more time and taking out from the grow tent in favour of leaving them on the window still.
As they start to outgrow their smaller pots, it's probably around the right time (temperature permitting) to start the hardening off process. As I start my tomatoes off under lights and on mats, this might be as simple as just switching off the heat mats for a few hours a day. Sooner or later though, they will need to be planted on, and this also sometimes means running out of room in the grow tent. When that happens, the plants are potted on and then moved into the polytunnel. If the evenings are forecast to get cold, I sometimes also add some fleece over the plants to protect them a little more. Now they are under natural light, they really do start to grow on, especially if the weather turns a little warmer.
While the plants are getting used to their larger pots and continue to grow, I can start thinking about preparing their final homes. For the most part, I grow my tomatoes outside, but if there is room in the polytunnel, I will often put a few plants under cover in there too. To make sure the ground is ready, I make sure it's weeded and also make sure that plenty of organic material has been added to the soil. I then use the tomato collars to mark out on the bed where the plants will go. When I first started growing tomatoes, I never got the spacing right, so now I make sure I leave a good amount of room between each plant.
Around this time is also a good time to add some companion plants around the edge of the beds. Here, I have chosen calendula and marigolds to do the job. Then comes the big plant out. Keeping a watch on the forecast, it's time to judge when the plants can get transferred outside. Something to remember is that though not hardy as such, tomatoes can deal with a little bit of cold should the temperatures dip into low single figures. They might not last for too many nights, but with a bit of fleece to keep the cold wind off, or any light frosts, they tend to pull through well. Another thing to remember is that once transplanted out, the plants can take a bit of time to settle into their new positions. Sometimes they will suffer a little bit of leaf curl, especially if they haven't been hardened off effectively. They may start to show signs of transplant shock. Again though, providing the timing and weather play ball, they'll get themselves established over the coming weeks and start to steadily put on more growth.
Depending on the variety (determinate or indeterminate) I add some canes or support structure for the growing plant. At this stage, it's important for me to just keep an eye on the growth, removing any suckers that appear, and also try to keep the lower part of the stem clear of growth to allow good air circulation around the base of the plant. As the weather continues to improve and the temperatures rise coming into summer, the plants will put on a growth spurt and start to produce flowers. At this point, I tend to start introducing a plant food into the weekly maintenance regime. It'll either be a specific tomato plant food like tomorite, or an all round liquid seaweed based food.
It's worth noting that at this point, if any of the plants were put into the polytunnel, they are treated in much the same way with the exception of watering. Should we have a wet period, then the outdoor plants won't get watered so much, but the plants in the polytunnel will still be watered, potentially several times a week. They also grow much quicker than the outdoor plants, but that's only to be expected.