The Hort Report: Use cold frame or hotbed to grow vegetables that could be ready by mid-March

Manure heated hotbed

The vegetables you can plant in a cold frame or hotbed starting as soon as the middle of January are chard, green onions, kale, mesclun, peas and spinach. | Diagram courtesy of UMC Guide G06965, Building and Using Hotbeds and Coldframes.

Hopefully, all of you made it through the first major snowfall of 2024. If you believe in the old wives’ tales, we should have a total of eight measurable snowfalls this year.

It was a heavy, wet snow. All the moisture in the snow will help build the subsoil moisture and seal up the soil around the roots of many types of plants, keeping them from dying this winter from the cold. 

I had a good friend and neighbor tell me she was going to start melting snow and putting it in containers to water her houseplants for the rest of the winter. Snow has nitrogen in it that helps all types of plants grow.

Do you want to be eating fresh vegetables that you have raised by March 15 this year? Think about building a cold frame or hotbed to grow your vegetables in. 

Select a location on the south side of a building so it gets plenty of sunlight. The more sunlight, the warmer the soil inside the cold frame or hotbed will get. 

You need four bales of straw or hay and an old window frame to make a usable cold frame. Arrange the bales around a mix of compost, organic matter and soil. You should have the mix be at least four inches.

Put two bales on edge to make the sides. One bale flat makes the front, and one bale on edge makes the back. Lay the window frame over the top of the bales. Seal up spaces around the window and bales with loose straw or hay. 

To make this a hotbed, add a heat source. I would use fresh manure. Put it under the soil mix. The manure will decompose over the next few years. You will need to add more manure to the hotbed each year to help create the needed heat. 

You can also use a heating mat or heating cables to help create the added heat that a hotbed creates over a cold frame. When using a heating cable, cover it with sand about one inch thick to help the heat spread more evenly.                                                                                 

The vegetables you can plant in a cold frame or hotbed starting as soon as the middle of January are chard, green onions, kale, mesclun, peas and spinach. Two weeks later, you can start beets, carrots, collards, greens and radishes. You also can transplant broccoli and cabbage into it.

Your vegetables should germinate within 7-14 days. It depends on how hot the soil gets and how much moisture they get. Once they germinate and start to grow, you will need to pay more attention to them. 

Make sure you water your vegetables as needed. Don’t overwater them, but don’t let the soil dry out.  

Raise the window off the bales if too much heat builds up inside. It can be like an oven inside, thus baking and burning young tender vegetable plants. Do this early in the day, only open for one to two hours.

Once the days get warmer and daylight is longer, leave the window off all day. Only having it on at night will help keep the soil warm at night.  

I have known people who have harvested produce all season long. You also can harden off transplants.    

If you get along this year with your cold frame or hotbed, you might want to build one out of wood for next year. You can dig down into the soil several inches. This will help keep the heat in the cold frame or hotbed better. 

I appreciate all your questions in the past and look forward to them in the future. Call me at 573-588-2040 at Shelby County Implement in Shelbina, Mo., come by to see me or email me at sci63468@hotmail.com.    

Pat Greenwell is the owner of Shelby County Implement in Shelbina, Mo. He was a high school agriculture teacher for 11 years. He has taught adult vocational agriculture since 1987. He also is a research assistant at the Truman State University Ag Department Farm. 

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