Sowing TomatoesSow tomatoes from late winter (Feb) to Spring (April). Seeds should be sown on top of a good organic (preferably peat-free) compost. You can use a special seed compost for this or you can use a good, fresh general purpose compost if you take out some of the larger pieces of material. Seeds should then be covered with about 0.5cm of potting mix, vermiculite or perlite and very gently watered in. Water from below by standing in a tray of water and letting the moisture soak upwards until the top looks moist, or use a fine watering can rose, or a bottle-top waterer. Seedlings will grow successfully in 3-4cm modules or sow 2 or 3 seeds per 7cm individual pots and take out the weakest seedlings.
Germinate at room temperature, or use a propagator set to 20C-25C. Grow the seedlings on in good light on a sunny windowsill or in a conservatory, keeping them at room temperature or at least, not lower than 15C to keep them growing strong. If it's too dark and warm the seedling will grow weak and thin. Seedlings in modules should be potted as soon as they start to look crowded, leaving them over-crowded and lead to stunted or straggly growth, which will set the plants back. Given half-decent warm conditions tomato plants will grow like weeds! If they get tall too tall you might have to give them some plant support even before they go into their final pot or grow-back.
Potting OnWhen the young plants are looking large for their pots, or if you can see white roots starting to make their way out of the bottom, pot the tomatoes on into bigger pots. Don't let them become pot-bound as thiswill stunt their growth. Some of the smaller, compact varieties of tomatoes can be grown in a 20cm pot, but most need something bigger. Outdoor and larger plants will need big heavy pots so that they are stable and don't blow over, and have enough potting mix to feed and provide water for the bigger plants. Choose pots that are 30cm or more in diameter. When you pot on your tomatoes it's best to plant them deeper than they were in the pot that you've taken them out of. Tomatoes produce "adventitious" roots (roots that grow out from the stem) when the stem is buried. You can plant them up to their first set of proper leaves if you have depth in the pot, this can help if your tomatoes have grown a bit leggy in the darker spring months, making the tomatoes a bit less floppy. The extra roots help the plants take up feed, water and stabilise them in the pot.
Small varieties of tomatoes grown indoors in conservatories, on windowsills or in greenhouses will grow happily in any good organic compost. Outside try this recommended potting mix for patio vegetables.
Keep them growing in a sunny spot until they are well established in their new pots. Grow bags do work very well for tomatoes, I use the Tomorite Giant grow bags in the conservatory. I keep trying peat-free versions, but they seem to vary hugely in quality and productivity from year to year, these are reliable. Sorry peat bogs. By the way, if you are using grow bags, grow can frames are, much better than the makeshift versions I've been using. I use Gardman Grow-Bag Cane Frame (Triple Pack) (they are <£5) which let me support a 7ft tall bamboo cane with no wobbles at all.
Types of TomatoIndeterminate or Cordon varieties need to be tied in to a tall sturdy stake and the side shoots pinched out (these are the leafy shoots that grow out between the junction of a leaf-branch and the main stem. Bush varieties are easier to care for and can largely be left to their own devices. A smaller stake can be inserted to stop them flopping under a large crop of tomatoes.
Moving Tomatoes Outside OutsideChoose outdoor bush varieties, they have good crops of tomatoes with excellent flavour and are much less work than Cordons. The time you choose to put your tomatoes outside should depend on the weather and whereabouts you are in the country. It's vital that young plants are not exposed to frost or low temperatures. Frost will likely kill them, and anything below 10C will cause the plant to sulk and stop growing for a while. So, you need to wait until the weather is consistently getting warmer at night. This could be May or June. Plants should be progressively acclimatised to the outdoors by placing them outside for a few hours, then a few more hours each day, over a period of 2 weeks. This is called hardening off. Use your judgment about placing the plants outside, if the weather turns bad, you can keep them in for a day or two.
Watering and FeedingTomatoes should be kept consistently watered, just most, never waterlogged and never allowed to dry out. If tomatoes are allowed to dry out it will always cause problems from yellowing leaves to splitting fruit. Larger pots require less frequent watering than small pots, pots in full sun will need more watering than pots that are in light shade for part of the day. A small plant in full sun may need watering every day. When you water, make sure you water deeply so that the water gets down to the roots where the plants need it, rather than just wetting the top where it will evaporate away. Tomatoes like to be fed regularly, either use a slow release organic fertiliser or use an organic liquid tomato food. For liquid foods dilute it to a quarter of the recommended strength and user every other watering for consistent feeding.
Pests and DiseasesOutdoor tomatoes are generally untroubled by pests. Occasionally they are troubled by aphids, which can usually be washed or pinched off. Indoors your plants may be attacked by whiteflies, which are both damaging and annoying. Whitefly can be controlled with an organic fatty-acid type spray (like Eradicoat) suitable for use on food crops. This suffocates the pests without damaging the plants. Heavy infestations may have to be treated with natural predators encarsia formosa, a parasitic wasp.
Both indoor and outdoor tomatoes can suffer from Blight, a common fungal infection that is worst in damp summers. The best response is to grow Blight resistant varieties in the first place and to avoid splashing leaves when watering. Remove and destroy any browned leaves.