In northern regions (and I mean way up north, above the 50th parallel, like in Alaska, the Yukon, Labrador, Northern Quebec and Ontario, and pretty much everywhere in the Prairie provinces), where it is difficult to grow most tender vegetables (tomatoes, peppers, potatoes, beans, etc.), consider growing them in old tires. Because of their black color, tires absorb heat from the sun during the day. The soil inside the tire will be up to 13˚F (7˚C) warmer than the soil in the ground surrounding it. And when the temperature drops at night, much of this heat is retained.
And don’t worry that the rubber tires will poison the soil. True enough, they contain tiny quantities of heavy metals… but then, so do garden soils! Also, rubber degrades very, very slowly, over hundreds of years, and will only release any such minerals very gradually, especially in the North. Besides, the only mineral present in used tires in quantities greater than are usually found in a typical garden soil is zinc, a mineral that plants need for their growth anyway.
As you approach the last frost date, place a tire horizontally on the ground and fill it with good rich soil. Two or three days later, when the soil has warmed up, plant your tender vegetables inside, then place a second tire over the top to protect them from cold winds (often a problem early in the season) and to warm up their leaves as well. Tires absorb so much heat that it is as though you were gardening at a latitude 10˚ further south, sometimes even 20˚! If ever the summer turns to be hotter than usual, simply remove the second tire. Oops! It suddenly gets cold again? Put the second tire back in place.
Note that the heat of the tires not only allows for earlier and safer planting in the spring and increased heat in the summer, but also extends the season in the fall. With a tire garden, you can often gain, 2, 3 or even 4 weeks of extra gardening time, enough to see even tomatoes and peppers ripen!
Too Hot for the South
You’ll find people using tire gardens further south as well, but it’s not always a good idea to use old tires in this way in areas with hot summers, because the tires tend to heat up too much and thus impair the growth of your vegetables. If you live north of the 50th parallel, though, or at a high altitude, that’s not going to be a problem!