There’s only one thing better than homegrown vine-ripened tomatoes and melons. That’s enjoying them sooner. There’s an easy and efficient way to coax tomatoes, cantaloupe, watermelon, peppers and all heat-loving vegetables to bear earlier: use clear plastic mulch to warm the soil.
I first heard of the technique about 45 years ago, as area universities were exploring ways to get melons to ripen earlier in northern climates, and I’ve been a fan of the method ever since, as clear plastic works wonderfully not only for earlier melons, but we can also use the technique on a few tomato plants to enjoy earlier fruits.
Warm-loving crops like tomatoes and melons require warm soil before their roots will grow. If transplanted into garden soil that’s below 55 degrees, the plants will remain inactive until the soil warms to the required threshold. If we can warm the soil more quickly in spring, then tomatoes and melons will begin growing faster, resulting in earlier and more prolific fruiting.
Clear plastic warms the soil more rapidly than black plastic. Clear plastic, laid on the soil, creates a greenhouse effect, letting warm sun penetrate and heat the soil, trapping the warmth below. Black plastic might feel warmer to the touch on a sunny day, but if you slide your hand under the black plastic, it’s cooler below the surface. Clear plastic warms the soil better.
Here’s how to use clear plastic for tomatoes and melons.
- Any clear plastic can be used. Rolls of 4 mil thickness are readily available at home improvement stores. 2 mil ‘painters plastic’ is too flimsy. The rolls are usually wider than needed, so cutting is necessary.
- Plastic can be laid down several weeks ahead of normal planting time to pre-warm the soil in late April or early May for the best head start. Or it can be laid down at planting time, which is usually about May 15 to 25 for warm season crops that are frost-sensitive.
- For individual plants, cut plastic squares 3 or 4 feet in size.
- For a whole row of tomatoes or melons, use a continuous plastic sheet, 3 or 4 feet wide by whatever length you want in your garden.
- After tilling or spading the soil, make a shallow furrow in the soil around the edges of where you want the plastic.
- Lay the plastic down on the soil, with the edges in the furrow, then cover the edges with soil.
- When planting time arrives, cut an ‘X’ shaped slit in the plastic, transplant the tomato or melon plants, then add a few handfuls of soil around the plant, to weight down the edges of the slit. Water in with a starter fertilizer solution.
- The plastic is best left on all season, and removed at fall cleanup time.
- Weeds might start under the plastic, but are quickly ‘solarized’ by summer sun as they’re trapped under the plastic.
- Rain reaches the plant through the initial opening, and as moisture moves in from the sides. If you prefer, you can poke a few holes in the plastic for additional moisture penetration, but it’s best not to. Too many holes allow precious warmth to escape and give weeds portals to escape. I don’t cut any additional holes.