For best results with the least risk, tomatoes should be planted when ______.

Tomatoes are generally easy to grow. Experts at the University of Illinois Extension suggest you start seeds indoors if the ground is still cold. For best results with the least risk, they say, plant when the soil is warm, soon after the frost-free date for your area.
    Be prepared to cover early plantings during the night if there is still a risk of freeze. Black plastic sheet can help keep them warm. When transplanting, use starter fertilizer.
    Small plants called dwarfs may be placed a third of a meter apart in rows. If you grow staked plants, set the sticks in the ground about half a meter apart. Some larger varieties of tomatoes may need about a meter between plants and at least a meter and a half between rows. The idea is to leave enough space for harvesting.
    Work the soil to remove weeds. But do not work the soil too deeply or you could damage the tomato plants.
    Water the plants regularly during long dry periods. Give them plenty of water. Plants in containers may need water daily or even more than once a day.
    Some gardeners train tomato plants to grow on cages. Whatever you choose, make sure the supports are tall enough. Most modern tomato plants grow about a meter tall. Others reach almost two meters.
    Experts at Purdue University Extension in Indiana say tomatoes started from seed take forty-five to ninety days till harvest. The average air temperature should be about twenty-four degrees Celsius. In that case, you can pick the tomatoes when they are firm and fully colored. But if the weather is very hot, pick the tomatoes every day or two. Let them soften and develop their full color indoors.
    There was a time when people thought tomatoes were poisonous. In fact, they are just the opposite.
    Tomatoes are good for you. But are they a fruit or a vegetable?
    Technically, a tomato is a fruit--the fruit of the tomato plant. As the experts at AskOxford.com explain: "True fruits are developed from the ovary in the base of the flower, and contain the seeds of the plant." But some fruits, including tomatoes, may be called "vegetables" because they are used in delicious foods instead of sweet cooking.