How to Use A Cold Frame to Garden In Winter Months

Written by Edward Harris

O hark unto thee, Winter. In Persephone’s absence, the bounty of my harvest hath passed, and my once verdant garden doth wither and fall.

Sure enough, a few weeks still lie ahead until the Old Farmer’s Almanac predicts the last frost for Zone 6, Dayton, Ohio in mid-April.

Luckily, there are numerous ways to extend the growing season, allowing eager gardeners to start up operations despite the gloomy skies and slushy soil. One of the most accessible options is the use of tried-and-true cold frames.

What is a cold frame?

Think of a cold frame as a mini-greenhouse. These small, bottomless enclosures have a transparent, angled top. This angle allows them to capture energy from the sun and uses it to maintain a higher internal temperature than the air outside.

This temperature differential allows for extended growing seasons, protection for cold-hardy crops, and as a protected space in which to start seeds. You can also use a cold frame to harden off tender seedlings before transplanting them into the soil.

How does a cold frame work?

The glass or plastic lid of a cold frame is angled toward the sun, typically facing toward the south. The angle of the top captures infrared energy from the sun and converts that energy into heat inside the enclosure.

Even on cold days, this allows temperatures within the enclosed space to reach 80 or 90 degrees. That’s why it’s important that the top of a cold frame can be opened, to vent excess heat during warmer, sunnier parts of the day.

What is a cold frame used for?

A cold frame creates an environment that’s effectively one hardiness zone more temperate than the outside. This means that plants can be started earlier in the spring, and continue to thrive later in the fall. This also means that more frost-tolerant crops can thrive deep into the winter. 

In the early spring, a cold frame can provide some extra runway for slow growing crops. Later in the spring, they can serve as additional nursery space for hardening off tender seedlings. You can start seeds in them for fall crops as well.

What crops benefit most from a cold frame?

In general, most crops can benefit from the protection and warmth provided by a cold frame, but some great uses include:

In winter, keep on growing:

  • Kale, and other greens
  • Mâche
  • Onions
  • Beets
  • Broccoli
  • Cauliflower

In early spring, get a head start on:

  • Tomatoes
  • Strawberries
  • Watermelon
  • Marigolds
  • Pansies
  • California Poppies
  • Bachelor’s Buttons

In late spring, protect young heat-loving crops like:

  • Cucumber
  • Peppers
  • Zucchini
  • Eggplant
  • Cosmos
  • Zinnias
  • Sweet Alyssum

In fall, keep on trucking with plants like:

  • Spinach
  • Lettuce
  • Radishes
  • Winter onions
  • Carrots
  • Beets
  • Parsley

What kind of cold frame is right for me?

There are many ways to create a cold frame, ranging from placing reclaimed window frames over bales of straw, to turn-key commercial kits with aluminum frames and thick, polycarbonate panels.

Outside of cost, the most important considerations are the internal volume, which should provide a balance between being small enough to efficiently warm up from the sunlight they capture, and being large enough to accommodate the plants you plan to grow. It’s also very important that the lid can be propped slightly open, in order to vent any excess heat, and to open up wide so that you can access the plants growing within.

Who can help me get the best results from my cold frame plants in Dayton Ohio?

As always, one of the best bets is to consult an expert. The helpful staff at Stockslager’s Greenhouse & Garden Center in Dayton, Ohio can offer lots of helpful advice on how to get the most out of your cold frames. Stop by today, and get something growing any time of year!

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