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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

Gardening: Use plastic milk jugs, plastic sheets, tarps to protect tender plants from spring frost, Munts says

I know everyone is champing at the bit to get gardens planted but let’s consider this. It’s been a whacky spring and we could still get a frost or two before June and beyond. At some point, however we will have to bite the trowel and plant if we have any hopes for tomatoes before fall frosts.

Traditionally, local garden lore says we can plant tomatoes and peppers when the snow is off Mica Peak to the southwest of Spokane. A quick look out my office window this week confirmed that there is still a lot of snow at the summit.

To protect small plants in the beds, cut the bottom out of a gallon milk jug with a cap and place a jug over each plant. If we get a really warm day, take the cap off to vent the warm air. Take the jugs off in early June when the plants start outgrowing them.

Stage some sheets, tarps or blankets in the garden to quickly cover tender plants if the forecast calls for near freezing temperatures. Because of the many microclimates we have here, your garden may easily get much colder than the predicted temperature. My garden at the base of the Painted Hills area can be five to seven degrees colder than the forecasted temperature at the National Weather Service office. Be sure to remove the covers in the morning so the plants don’t overheat.

Tender crops can also be protected with floating row cover, a spun polyester fabric that traps heat near the plants but lets light, air and water through. The fabric can be supported above the plants on hoops of heavy wire or half-inch PVC pipe. An added benefit of the fabric is that it can be left on the plants well into June and provide a cozy warm environment that will jump-start their growth. The fabric can be found at some garden centers like Northwest Seed and Pet or purchased online.

One unusual method for keeping frost at bay is to turn on overhead sprinklers overnight. The water freezes around the plants encasing them in a protective coating of ice. Once the ice melts, the plants are fine. This works because as the water turns to ice, it gives off just enough heat to keep the plant tissues from freezing. I saved a whole crop of pepper plants this way one year.

Lastly, our soil hasn’t had much time to warm up this spring, and that can stunt any tender crops like tomatoes if they are planted in it. To help warm the soil quicker, lay black plastic over the area you are going to plant and then cut holes and plant through the plastic. The plastic will trap the sun’s heat and warm the ground enough for the plants to thrive. If you are using drip irrigation, lay the hose under the plastic. The plastic will also help to reduce evaporation from the soil later in the summer.

Pat Munts has gardened in the Spokane Valley for over 35 years. She is co-author of “Northwest Gardener’s Handbook” with Susan Mulvihill. She can be reached at