When do you plant tomatoes? If you visit a nursery this weekend, you'd certainly think now, because packs of little tomato plants line the benches. If you listen to conventional garden wisdom, you might wait until the weather is warmer, in May.
I always plant too late, waiting until June, and I seldom get any tomatoes until late August, with tomatoes lingering on the vine until November. They don't go to waste, but much of summer is spent without tomatoes, a sorry state.
But more gardeners plant too early and then wonder why their plants have flowers but no fruit. The answer is that tomato flowers don't make fruit until the weather is reasonably warm, so if the first flowers open during the foggy, cool weather of May and early June, they aren't likely to produce tomatoes.
Night temperatures must be between 55 and 75 degrees for fruit to set; daytime temperatures are relatively unimportant. If the nights are cooler than 55, there will be no fruit, but you also get no fruit if the nights are warmer than 75 degrees, which is why blossoms often drop off in midsummer without producing fruit, a common occurrence in the San Fernando Valley.
So, when is just right? My favorite reference book says that the tomato-planting season begins mid-March, though admittedly the information is a trifle out of date since "Vegetables in the California Garden" by Ross H. Gast, was published in 1933, and much has happened to tomatoes in the ensuing years. For one, there are now "early" varieties that don't need as much nighttime warmth to set fruit.
In coastal areas, where a foggy spring is a sure bet, these are what should be planted now. Two of the most obtainable are "Early Girl" and "Sweet 100." I had to search through the many other varieties to find them at my local nursery, but they were there. "Early Girl" is a normal-size tomato, a "determinate" type, which means it usually grows about three feet tall and then stops. "Sweet 100" is a cherry tomato and is "indeterminate," which means there is no stopping it until frost blackens its foliage. Indeterminate tomatoes can grow as tall as a house and frequently do.
Thus, knowing if you are planting a determinate or indeterminate tomato variety is essential. The one is quite manageable, the other requires massive support, or pruning. Unfortunately, this information is seldom on the plant label. Of the common tomato varieties I see at nurseries, these are determinate--"Pearson Improved," "Ace," "Celebrity," "Roma" (for paste) and "Patio" (for containers)--and require only short stakes or small wire cages, which are usually sold at nurseries. These are the least work to grow.
But if you want lots of tomatoes in little space, you should construct a big wire cage of concrete reinforcing wire with a six-inch mesh, about six feet tall by two feet across, or put in a tall sturdy stake, and grow the indeterminate varieties such as "Better Boy," "Big Boy," "Golden Boy," "Beefsteak," "Beefmaster" or "Pink Ponderosa." There is no stopping these.
So, the answer to the original question of when to plant is determined by where you live and what variety you are planting. Anywhere, this weekend, you can plant the early varieties. Near the coast, you can take a chance on the others or wait until the more sure-fire month of April. Inland, in the hotter interior climates where fruit set is going to be a problem in summer, you can plant any variety this weekend, but you can also plant in April.
You can start tomatoes from seed, but since most of us only need a few plants, buying them as seedlings at nurseries makes more sense.
How do you plant a tomato? Deep. After preparing the soil and mixing in some fertilizer, you should plant the seedling so all of the stem, up to the first set of leaves, is buried and underground. This would instantly kill most seedlings, but tomatoes will form roots all along that buried stem and be better off for it. In experiments carried out by Ortho Books, vines planted deep were twice the size after 30 days of growth. Be sure to firm the soil down so there are no air pockets (but don't break those brittle stems) and water thoroughly, even if it does rain this weekend.