Keeping vegetables warm and growing | Kitsap Week

A hoop house is one method of keeping plants warm during the cold season.  - Melinda Weer / North Kitsap Herald
A hoop house is one method of keeping plants warm during the cold season.
— image credit: Melinda Weer / North Kitsap Herald

Do you want tomatoes that actually ripen? How about lettuce that doesn’t wilt with every cold snap? Maybe you’d just be happy if some of your seeds actually germinated.

It sounds like you could benefit from advice on how to keep your vegetable plants warm.

In Kitsap, we face the dual challenge of skies that are more often cloudy than sunny and temperatures that never really climb as high as we’d like them to. The result is cold soil and cold, sun-hungry plants. Don’t despair — there are a number of low-cost ways in which to warm up your backyard crops.

Cold frames

Cold frames are essentially large boxes with lids made from translucent or clear material. You can build a frame around an existing bed or build a planter box with a frame on top. My husband built a planter box for summer flowers. When the chill of autumn began, he built a cold frame on top. The lid is made out of a large, old window that I bought on Craigslist.

On warm days, you prop the lid up with a stick. Cold frames are often built with the idea that you can move them around as needed. In the hottest part of summer, put them aside.

It’s best to mount the lid so that it is higher in the back than the front. Then, align the cold frame so the angled surface faces south. You want to soak as much sun into that box as possible.

I’ve had great success growing lettuce, spinach, radishes, green onions, and chives in our cold frame. Most cold frames are built low to the ground, so don’t plan to plant taller vegetables in them.

Hoop house

You were expecting me to list greenhouses next, weren’t you? But, have you considered a hoop house?

Hoop houses are low-cost alternatives to greenhouses that are easy to build. Basically, they are buildings made out of steel half-hoops and covered with clear plastic. I bought a kit from Steve’s Greenhouses ( There is a great gallery on his website to give you some ideas.

We’ve found, to our delight, that hoop houses are fairly easy to move. We originally constructed ours on our farm in Sandy, Ore. When we moved to Poulsbo, we dismantled it, labelled and folded everything, then put it back together at our new farm.

We discovered the spot where we originally located it did not have the best sun. So, my husband put a couple of dollies under the back corners, attached the front to the back of his lawn tractor, and easily towed the hoop house to a new location. Now, that’s portability!


I collect large pots from nurseries, fill them with rich soil and then plant seeds or transplants in them. Pots are easy to move around and easy to weed. They also keep the soil warmer.

I like pots because I can pull them all outside when it is time to scrub down the inside of the plastic. Keeping your plastic clear of green gunk will ensure your plants get the sun they need.

It is helpful to add a couple of large barrels filled with water to help retain heat. You may also wish to add a window for cross-ventilation in summer, or use a box fan for that purpose.

Indoor starts

Our growing season can be short. It’s a good idea to start plants indoors and then move them outside once the soil warms up. Growing indoors is not as difficult as you might think. All you really need are fluorescent light fixtures and pots or trays in which to grow your baby plants. I grew my starts on a folding table by a sunny window.

You can start your seeds in peat pots, egg cartons, small starter greenhouses, or even yogurt containers filled with potting soil. I poked holes in the bottom of yogurt containers and then set them in plastic trays so I could water them in the house without worrying about leaks.

Mount fluorescent light fixtures above the plants for extra light. Keep the lights on for 12 hours a day. I varied the height of the lights so they were always about 6 inches above the top of my seedlings. Start by resting the ends of the lights on soup cans, then large juice cans, and work your way up. You can even put a seedling warming mat underneath your containers to help your seeds germinate even faster.

Raised beds

If you want to grow better vegetables here in the Pacific Northwest and keep your soil warm, raised beds are great. Soil in raised beds also drains better, which helps to keep the soil warm.

You can really be creative when building raised beds: construct a frame out of wood, use old tires, or place railroad ties, cinder blocks or straw bales in a rectangle.

You want to fill your raised bed with quality, weed-free soil. I fill mine with comforter compost during the winter; a composting method where you spread organic matter over the bed in layers. As the layers decompose, they will create a wonderful, rich mulch. Cover the layers with black plastic to retain the warmth.

When I first transplant seedlings in the early spring, I just poke a hole in the plastic. But, remember to remove the plastic later in spring so the sun can warm the soil. The downside of using plastic is that slugs love to live beneath it.

For more information on how to grow vegetables in the Pacific Northwest, web-footed gardeners swear by Steve Solomon’s “Growing Vegetables West of the Cascades, Updated 6th Edition: The Complete Guide to Organic Gardening.” Kitsap Regional Library has copies on hand.

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