EXTEND GROWING SEASON WITH A COLD FRAME

January 18, 2019

Succulents that withstand fairly cool temperatures and do not need as much light as early vegetables and annuals are placed in the cold frame consisting of the shower door top.  If temperatures fall below freezing, the whole structure can be covered with an old blanket for protection.

Materials for cold frame

Various possibilities can meet space/budget requirements:

Walls

• Wooden boards, preferably 2 inches thick
• Landscape timbers
• Bricks or concrete blocks
• Hay bales

Tops/covers

• Old windows
• Old glass doors
• Clear plastic stretched on frame or hoops
• Clear fiberglass

An internet search will reveal numerous types of cold-frame structures.



Controlling heat, moisture

• Open or remove top on warm days
• Use electric lift devices
• Heat cables buried in ground or attached to box
• Heat lamp or Christmas tree lights
• Bags stuffed with leaves to place on top or around sides
• Blanket covers for cold nights



PHOTO BY BRENDA HEINOLD/VICTORIA COUNTY MASTER GARDENER

This cold frame is constructed with landscape timbers hugging the ground topped with a recycled shower door.  Its size and shape are a result of the glass top, which makes it an approximate 27-inch-by-69-inch box with a lid or top that can be slid to the side or removed altogether depending on the plants' needs for ventilation, light and heat of the day.

Every January, I start dreaming of the warmer days of spring when I can set out vegetable plants and flowering annuals.

Disappointing outcome of efforts

Over the last several years, I have tried to start my own transplants from seeds, many of which my gardening friends have shared with me or I have harvested myself. I have also started seeds purchased from seed catalogs or local nurseries. The result is often disappointing.

Although the seeds sprout, the plants usually fail to grow at all or get extremely spindly, eventually dying before the weather warms sufficiently to transplant them in the garden. I have used grow lights but have found them to be inadequate and too expensive.

New experiment with cold frames

This year, I have decided to experiment with cold frames. What is a cold frame, and why should I consider it?

A cold frame is a bottomless box built close to the ground, or even partially dug into the ground, and topped with a transparent cover. The sides of the frame hold in heat, and the transparent top allows the sun to warm the space and provide the light that the plants need to grow well. To prevent excessive heat and condensation, the top must be able to be opened.

Cold frames are far more affordable than greenhouses, relying primarily on passive heating from the sun.

• Variety of materials from which to build the frame

The box can be built from a variety of materials as can the transparent top. Refer to the adjoining information for a list of suggested possibilities.

Size, style determined by materials

The size and style of your cold frame might be dictated by available materials. In my case, I have an old aluminum-framed, glass shower door that will serve as the top of one cold frame. The door measures 27 inches by 69 inches, so that will be the approximate size of my box.

The box is made of landscape timbers stacked atop one another. The glass door is simply laid on top of the timbers. I plan to use this cold frame to grow succulents that can withstand fairly cool temperatures and do not need as much light as vegetables and flowering annuals.

To vent the frame during the day, I can simply remove the glass top, or slide it off to one side. Since this particular frame is not insulated and is not particularly airtight, I do not believe that venting will be much of a problem. If the temperatures are forecast to fall below freezing, I will cover the entire frame with an old blanket.

Second cold frame to house young plants

To get my vegetables and flowers off to a good start, I am building a second cold frame. It will be used to house the young plants until they can be placed in the garden.

• Designed to get more light and protect from cold

This cold frame is designed to capture more light and provide better insulation from the cold. The frame is made from 2-inch-by-8-inch pressure-treated lumber, salvaged from a backyard pergola that was destroyed by Hurricane Harvey. The top is an old wooden window that measures 28 inches by 36 inches.

• Top dictates size

Once again, the top dictates the size of the cold frame. If I did not already have a window, I would have built a simple frame from 1-inch-by-2-inch lumber and would have stapled plastic to it to form the top. In that case, the cold frame could be any size that works well for my space.

• Angled sides help capture more light/heat

The sides are angled so that the back of the box is approximately 8 inches taller than the front. The window is attached by hinges to the back of the frame. The top rests on the sloping sides and, therefore, is angled toward the sun, capturing even more light and heat.

The top can be propped open during the day to control excessive heat and moisture buildup. If the temperature drops very low, I will add Christmas lights to the inside of the box to add a heat.

• Located on south-facing wall

I am placing this cold frame against a south-facing wall. If a south-facing wall were unavailable, extra insulation could be added by attaching a foam board to the inside. Bags containing leaves or hay can be piled around the sides and more bags can be piled on top to provide extra insulation at night.

Consider a cold frame

Consider adding a cold frame to your garden this year. Explore the many styles and plans available. They are affordable, can be built quickly and can extend your growing season.

The Gardeners’ Dirt is written by members of the Victoria County Master Gardener Association, an educational outreach of Texas A&M AgriLife Extension – Victoria County. Mail your questions in care of the Advocate, P.O. Box 1518, Victoria, TX 77901; or vcmga@vicad.com, or comment on this column at VictoriaAdvocate.com.