Tomatoes plants have three main requirements- sun, water, and a well-drained, rich soil. The more sun you can get your plants the larger your yield. You really need at least 7 hours of June sunlight per day to grow decent plants, and 12 hours should get you beautiful plants, with a lot of tomatoes.
Your soil needs to be well-drained, whether in a container or in your garden. We recommend a mix of 20% sand, 20% perlite (or peat, although perlite is far superior), and 60% compost for containers. If you are planting in an outdoor garden it never hurts to condition the soil with sand and compost. When purchasing sand, be certain you do not use sandbox sand- you want "cut" or "builders" sand, although Quickrete-brand all-purpose sand works well too. Make sure you don't accidentally buy the concrete mix!
Start seeds under soft-white fluorescent lights 7-8 weeks before soil temperatures in your area reach 62F, and the danger of frost is past. Don't worry about buying the expensive "grow lights" as the soft-whites work just as well. The shoplight hanging fixtures cost $8 or $9 at Lowe's or Home Depot. If you buy two of them, 4 bulbs, and a cheap timer your total investment shouldn't exceed $25.
Start seeds in trays filled with seed starter mix or use jiffy pellets. Make sure that your trays are adequately drained and that you have your lights about 1 inch above the soil. The preferred air temperature is at least 67F, with warmer being better. Your lights should be on for 12 to 14 hours a day- a timer works well for this. Once the seeds have sprouted you will want to adjust the lights so that they are within 1 inch of the leaves. If the lights are too high, the plants become leggy (tall and skinny). Don't worry too much about the leaves touching the light bulbs.
It is possible to grow tomatoes in a window, although I have never had much success with this technique. You really need a bay window, facing south, to get the job done.
Once the plants have reached a size (2") where they are crowding each other in the trays, or roots are starting to emerge from the netting around the Jiify pellets, you will want to transfer them to 3.5" or similar pots. Mum pots work well for this, as do 16-ounce plastic cups with holes punched in the bottom. Plants will not become rootbound when planted in these containers until they reach 12 to 14 inches in height. When you transplant them take care not to damage the roots, and make sure the mix in the receiving pot is moist. Seedling roots die almost immediately when exposed to air or dry planting mix. Pepper seedlings need to transplanted at the same soil level, while tomato seedlings can be planted deep enough that the soil is over the first set of leaves (remove them first by plucking, not tearing).
Keep the plants under lights for 13-14 hours per day until it is warm enough to take them outside for a few 70F+ afternoons. Take care to keep them sheltered from the wind. Make sure they don't spend more than 15 minutes in direct sunlight the first day as the leaves will sunburn- it's best to start in the shade for a day or two, then work yourself to part shade, and then full exposure. If the low temperature will remain above 52F you can leave them outside overnight.
After a few days you can leave them in direct sunlight for an hour or so. Gradually acclimatize to direct sunlight, and don't expose to temperatures under 52F. Once your garden (or container) soil temperature reaches 62F, you can plant (provided you won't see more than a couple nights in the 40's). If you plant too soon, the roots get chilled and the plant never fully recovers.
Plant tomato seedlings deep! You can pull off the bottom two leaves and bury it up to the next set of leaves. They will form roots on any portion of the plant that is in contact with moist soil. Now, here is where many tomato gardeners fail. They rush to get their plants in the ground as early as possible. Big mistake! When you dig your hole you want to feel soil that is not cool to the touch. If it is, leave the hole open for at least a week to allow the soil to warm sufficiently. If you have a thermometer, use it. I always pour a bucket of warm water in the holes about 20 minutes before I plant.
Many people wonder how large their tomato plants should be when placed in the garden (or large container). The plants pictured below are ideal in size (left pepper, right tomato). You generally don't want fruit to be forming on your plants, but flowers are fine.
When you remove the plant from the pot take care not to bend the stem. You can gently pull the roots apart so that they aren't tangled.
The Perfect Size to Transplant
Tomatoes do great in containers. In fact, I have found that they consistently perform better in 15-gallon containers than in the garden. Anything under 7 gallons is a waste of time without fertilization. You may grow a nice-looking plant, but few tomatoes will be present. There simply isn't enough soil volume to provide the roots with enough room to grow.
It should be noted that container soil is much warmer than garden soil during most of the season. This gives container gardens a distinct advantage during the early season, but can cause some problems in July and August. When daily high temperatures reach the high 80's and 90's, you really need to liberally water all container plants on a daily basis. This helps to keep the soil temperature below 80F. The Cherokee Purple shown below (16" container) yielded 36 tomatoes last year. This picture was taken 3-4 weeks after transplant.
Almost all tomatoes should be staked unless you can tie it to a fence or railing, like I did above. I have found that the vinyl-coated stakes available at Home Depot and Lowe's work well. Tomato cages and boxes work great too. You can let tomato plants grow along the ground (un-staked) but you will find that the insects beat you to many of the fruit.
When I was a kid everyone said you had to prune, or "sucker", tomato plants. Supposedly the suckers would suck all the energy out of the plant. It's a great theory, the only problem is that the suckers grow tomatoes too. My personal experience has shown no real difference in production between pruned plants and non-pruned plants.
Depending upon which part of the country you live in, pollination can be an afterthought, or a real problem. In Central Ohio we get a lot of warm humid nights during the month of June where the temperature doesn't fall below 70F. During these hot, humid periods pollination of tomato plants is difficult. One theory claims that the pollen grains become too sticky, and thus are difficult to transfer. I tend to agree. This problem becomes evident when you have a beautiful tomato plant, but few fruit. The best you can do is hope the weather changes, or do a google search for "manual tomato pollination". It's really not that difficult. You should also be aware that, contrary to popular belief, honeybees are not the primary pollinator of tomato plants in most parts of the U.S. In Ohio they are responsible for only about 30% of pollination, while a tiny green-eyed fly handles the majority of the load. This is typical in other parts of the country too.
I gave up using synthetic fertilizers about 5 years ago and now rely solely upon composted cow and chicken manure. I have found that my yields are better using natural fertilizers, and my plants are healthier. If you have trouble finding natural compost there are some excellent organic fertilizers at your garden store. I have heard very good things about Tomato-tone but have little personal experience with it.
Water plants every 3-5 days, depending upon rainfall. Tomatoes generally like around 4-5 inches of rainfall per month. Plants will start to wilt if they need water.
An inch of water in a container is exactly what it sounds like- pour water into the pot so that about 1 inch is present before it soaks into the soil. Containers, however, require a lot more water than an in-ground garden. When daytime temperatures reach the high 80's I tend to water the garden every other day, and container plants daily.
You should always use cool water. Some rain barrels can practically boil water if exposed to the sun for too long.
A common problem that faces tomato growers in the Midwest and East is blossom-end rot. You may have read that it is caused by "inconsistent watering"; this is usually not the case. This problem is almost always caused by a lack of calcium in the soil. It is quite easy to correct- add crushed, cooked (hardboiled) eggshells around the plants at a rate of 3 or 4 eggshells per plant. Another excellent soil additive is crushed oyster shells. They are available from several online vendors.
If you are a tobacco user, either smoker or chewer, you need to wash your hand well prior to handling your seeds and plants. You can infect your garden with the tobacco mosaic virus (tmv), which affects both tomatoes and peppers.