Gardening with a Cold Frame to Extend the Growing Season

I am completely fascinated by cold frames because of their ability to shelter plants and extend the growing season in the garden. It’s a delight to peer into the clear cover and see thriving green plants within. It’s not too late to create a cold frame and plant in it. September is a good month for planting seeds in the cold frame for a harvest in November-December. Here are some great ideas to help get you started!

Add a cold frame to your existing vegetable garden

A small cold frame made with bricks and a glass cupboard door. Perfect for some salad crop.

A small cold frame made with bricks and a glass cupboard door. Perfect for a small batch of salad greens.

 

Add a cold frame to a raised flower box 

This shows an easy way to convert a plastic vinyl raised flower box into a cold frame.

This shows an easy way to convert a 3′ x 3′ plastic vinyl raised flower box into a cold frame. The polycarbonate accessory easily attached on top.

Place it where it will receive the most sunlight. The south side of a home will be the brightest and warmest location.

The materials needed to create a cold frame are extremely simple and easy to find. You may have some of the materials in your backyard or garage.

The frame can be made with straw bales, bricks, concrete blocks, plastic vinyl or wood. It is best to use non-toxic plastic vinyl or untreated wood, especially for food production. If possible, angle the frame to allow more light to enter. A typical cold frame dimension is 3′ x 6′ but this can vary depending on the available space and materials used. The height of a cold frame is usually 1′-3′ to accommodate the growth of the plants.

The cover of the cold frame can be repurposed glass from doors or windows. Patio doors, shower doors or windows can simply be placed on top of the frame or attached with hinges.  A clear plastic cover works well too, such as 4 mil polyethylene film, corrugated polycarbonate plastic or twinwall polycarbonate plastic. Plastic can be attached to a wooden frame and either place on top of the cold frame or hinged to help secure it in place.

Prepare the soil by cultivating it with a trowel or shovel. Add organic container soil mix or a triple soil mix containing compost, peat moss and earth. This will help condition the soil by adding organic material and nutrients. If possible, place straw bales or soil around the outside of the cold frame for better insulation.

The fun part is planting the seeds!

It can be difficult to find seeds late summer. William Dam Seeds was fully stocked.

Seeds appropriate for planting in a cold frame in September:

  • Spinach
  • Radishes
  • Mizuna
  • Lettuce ‘Winter Density’ and ‘Red Salad Bowl’
  • Mache also known as corn lettuce or lamb’s lettuce

Plant the seeds in rows by creating furrows in the soil using your hand or trowel. Lightly cover the seeds with soil and gently water.

The soil is slower to dry out during the cooler months of the year. You may not need to water the soil in the cold frame that often but check a couple of times a week for watering. Keep the soil surface moist after planting seeds and then allow the soil surface to dry in between watering once the seeds have germinated.

The cold frame will need daily attention! Keep the cover closed when it’s cold and cloudy and prop open for ventilation when it’s warm and sunny.

Bricks or a stick can be used to prop the cover up for ventilation

Bricks or a stick can be used to prop the cover open for ventilation

Harvest the tender leafy greens in November-December when they are over several inches tall. Harvest on a fairly mild day when the temperature is not freezing and the plants are not frozen. Add your leafy greens to a salad or use them to garnish a meal.

Happy Growing,

Trina Alix

 

Reference:

  • Coleman, E. The Winter Harvest Handbook. Chelsea Green Publishing, 2009.
  • Meyer, S. Make Your Own Cold Frame. Organic Gardening. 41.8(1994): 42.
  • Colorado Master Gardener Program. “Frost Protection And Extending The Growing Season.” ext.colastate.edu/mg/gardennotes/722.html. Colorado State University Extension.