Week to cover-up

Mesclun growing under row cover fabric

A week of 30 mph winds on Colorado's Front Range with both daytime and nighttime temperatures below seasonal averages presents a great opportunity to talk about plant protection and season extension "cover-ups".

Using floating row cover fabric to grow early spring crops made even more sense this week. With soil covering the edges, this lightweight, spunbonded polyester or polypropylene fabric stays in place even though it flaps in the wind. Indeed it should be loose for plants to grow. The fabric provides just enough tempering to moderate wind and cold temperatures while water and light penetrate for plant growth.

If you haven't tried growing under row covers, do so to realize the benefits including wind protection; earlier and increased harvest; pest protection from insects, rabbits and squirrels; frost protection; water conservation and more (see here). Many local market growers are making extensive use of fabric covers for field production. They work equally well in home gardens. Just be sure to peek under the cover once in a while. Weeds find the tempered environment equally conducive for growth and you don't want to miss peak harvest quality because crops are "out of sight, out of mind".

Wall O' Waters set up to warm soil

Another forward looking cover-up this week is preparation for early planting of warm season vegetables. Use of Wall O' Waters to warm soil for future planting of tomatoes and other warm season crops made sense after last weeks warm weather and before this weeks cool-down. Made in Dillon, Montana, this product has a proven record of enabling home gardeners to plant earlier and protect tomatoes from winds and frost. The water-filled channels in the sides are heated by the sun to warm the soil and then protect the plant inside. The manufacturer recommends setting them up at least a week prior to planting to allow for warming the soil for roots.

Wall O' Waters used with black plastic mulch

Wall O' Waters can be used either alone or in combination with another cover-up, black plastic mulch. Even though clear plastic works better for warming soil, black plastic does a fair job and can be used around water walls to prep a garden soil even more for an early May planting of warm season crops. Yes, our average last frost in Denver is May 5 but cold weather often extends later in the month. Plant protection and season extension make sense in our climate.

Photo credit: Mesclun growing under fabric row cover, Wall O' Waters set up to warm soil, Wall O' Waters used in combination with black plastic mulch - All credit Carl Wilson.

Extending the season in fall

The decision about what action to take with impending fall frosts can be complex. That’s probably why many simply throw a cover over their warm season crops (peppers in photo, tomatoes, etc.) and hope for the best.

The rhythm of the seasons with shortening days and cooler temperatures really speaks against fighting the trend. Harvesting tomatoes and letting them ripen indoors as discussed in the September 17 post may be a better choice in many ways. Cold temperatures destroy flavor and chilling injury decreases “shelf life” of the fruit leaving them open to decay. Room temperature indoors eliminates both problems.

Tomatoes will not be setting more fruit in cool temperatures so saving green plants is not productive from that standpoint. Concentrating on soil improvement by removing warm season plants to the compost bin and planting a cover crop as discussed last week may be a better use of a gardener’s energy.

Cool season greens planted in mid-summer (kale and mesclun in photo) tolerate frosts well. They may be more productive for the water applied in fall than warm season plants. Maturing root crops will also survive initial frosts and store well in the garden until dug for use.

Covers can perform well in radiational frosts experienced under clear nights. Cloth (photo left) will trap soil heat with the plants and is fine as long as it doesn’t get wet. Wet cloth loses heat due to evaporative cooling. Plastic traps heat and doesn’t have evaporative losses due to moisture but must be removed promptly the following sunny day to avoid cooking plants. Do remove any cover the next day to allow the sun to warm the soil again.

See CSU Extension Garden Note on Frost Protection and Extending the Garden Season for more extensive information including comments on use of space blankets and Christmas tree lights under covers.

Photo credit: Plastic to cover peppers, mid-summer planted greens, fabric covered tomatoes, all credit Carl Wilson

Season extenders for early birds

The Front Range’s mid-May average last frost date means it’s still too early to plant warm season vegetables such as tomatoes, eggplant, peppers and squash. Or is it?

Transplanting vegetables instead of direct garden seeding is one way of extending the growing season. You or your greenhouse grower typically start seed indoors 6 to 8 weeks before plants can be transplanted to the garden. Coddling plants inside when outdoor weather is still too cold gains you valuable “days to maturity” necessary for longer season vegetables to achieve the goal of producing fruit.

Another tool is in-garden season extenders. Products include Wall O’Water® (being filled with water right), Season Starter™ and Kozy Coat™. These plastic cones with water channels in the side use sound principles of physics to keep plants warm. The water absorbs heat from our abundant sunshine by day and releases it at night. Regulate the temperature in the cone by nudging the top open to ventilate on warm days and closed during cloudy weather and cold nights. Plant as much as a month early in April with these devices.

Remember that the mid-May average last frost date is just an average and can vary a month either direction. The snowy garden photo left was taken in Denver on May 24, 2002. Unless season extenders are used to minimize risk, playing the last frost average too closely can trip-up gardeners. This is why some risk-adverse gardeners don’t plant tomatoes until Memorial Day.

Keep in mind that extending the season is much more than frost protection provided by a sheet thrown over plants. It’s about keeping plants warm at night. Tomatoes in particular are markedly set back by nights cooler than 55 degrees F. They simply stop growing even though they haven’t frozen.

While growth is halted by night temperatures in the high thirties or forties, you lose valuable days and weeks in the quest for the necessary days to maturity in our short growing season. It takes plants days and even a week to resume active growth even when night temperatures warm.

Commercial plastic cones with water channels or home-rigged plastic milk jugs filled with water and circled around plants (photo with bean plant right) are valuable in extending our growing season. If you’re itching to plant early, season extenders are a must.

See the CSU Extension Garden Note on Frost Protection and Extending the Garden Season for more information.