Fear frost no more

By Kim Tuscano March 2023

Learn how to get a jump start on planting tomatoes with walls of water

Tomatoes are warm-weather crops. They like their roots nestled in a warm, cozy soil and are sensitive to freezing temperatures. Even a light frost can kill tomato plants, so they are typically planted after the threat of frost has passed—late March in southeastern Oklahoma and as late as April 30th in the panhandle. Yet there are advantages to getting a jump start on planting tomatoes in the garden.

In addition to bragging rights for producing the first ripe tomato on your block, starting tomato plants early helps ensure a good harvest before temperatures soar. Though tomatoes are heat-loving plants, they commonly drop their flowers when temperatures get too high. This occurs when daytime temperatures exceed 85 F and night temperatures are above 70 F for several days and nights. In Oklahoma, summer temperatures reach this critical range early in the growing season, causing flowers to drop and fruit production to slow or stop until cooler temperatures return.

This is where early planting comes in. But how do you overcome the threat of frost? You don’t need a greenhouse to beat the cold. Several inexpensive materials can be used to protect young tomato plants including old-fashioned glass cloches, milk jugs and soda bottles. For even more protection, consider using walls of water, which can be purchased at many garden centers or ordered online. 

Walls of water are double-walled, plastic plant insulators designed to hold water. They create an insulating ring that moderates the temperature around the plant and protects plants from freezing.  Each one is constructed of a series of vertical cells that you fill with water. The water absorbs heat during the day and releases it at night, keeping plants warm even when air temperatures drop below freezing. Walls of water can be used to start tomatoes, peppers, squash and other plants four to six weeks before the average last frost date for your area. 

Here’s how to use them:

1. Set up insulators one week before planting seedlings to warm the soil. This step is important, as tomato plants can be stunted by cold soils. Use a bucket to hold the walls open as you set them in place. Bury the bottom an inch or so into the soil for stability. Be sure to set insulators at the appropriate spacing for plants, approximately 2 feet apart depending on the tomato variety.
2. Fill cells two-thirds full with water and remove the bucket. The walls will fold together at the top, trapping heat inside and warming the soil below. 
3. Transplant tomato seedlings into the center of each wall of water. Use small, 3- to 4-inch plants as they will experience less transplant shock. You may wish to set a plant stake at this time, which will hold the wall of water open as you work. It can be difficult to work through the opening; a bulb digger can be helpful for digging. 
4. The plastic walls allow plenty of light to penetrate and nurture the growing tomato plant while keeping it warm day and night. After several weeks, plants will start emerging through the top of the insulators. At this time, fill the wall of water cells completely, which will hold the top open. Remove insulators after all threat of frost has passed. 

By taking measures to protect plants from frost, we can jump-start tomato production and enjoy an early harvest. Also consider early ripening and heat-tolerant tomato varieties as additional ways to beat the heat.