How to Make a Hot Bed For Tender Plants

Gardeners trying to grow their own food, or tender ornamental plants will soon find that they are up again the challenges of a short growing season and winter frosts. Sometimes, it can be a challenge to provide plants with the protection that they need from chilly weather and cold soil can quickly kill off crops sown too early or too late. A hot bed is one way in which you can solve these problems.

What is a Hot Bed?

A hot bed is a raised bed that contains organic matter (usually straw and manure) that will compost in place. As these materials break down, they will generate a surprising amount of heat. When topped with a layer of growing medium, the heat from these decomposing materials will provide a little extra bottom heat for growing plants, warming the soil and roots and keeping frosts at bay.

A hot bed can be created outside in your garden, in a polytunnel or greenhouse, or even in a light, bright garden building, and can allow you to grow for a longer period of the year, and to consider more tender and warmth-loving plants than you might otherwise have been able to.

For even more protection from the cold, a hot bed can also be covered with a cloche, row cover, mini polytunnel, or cold frame to retain the heat and make an even warmer habitat for your plants.

How To Make a Hot Bed

Before you bring in your organic materials to compost in place to generate heat for your hot bed, you will need to consider what you will use to retain the materials. Almost any large container could potentially be used, and there are plenty of upcycling projects that you could consider.

For example, you could use an old bath, or metal trough. You could upcycle a barrel or another large container. You could also construct the sides of your raised hot bed from any number of natural or recycled materials.

Where heat retention is a primary concern, it could be a good idea to use materials such as rock, brick or ceramics, which have a high thermal mass. You could also consider how you might be able to create a cob structure, using clay – you might even be able to use clay from your own garden. Materials with a high thermal mass will help to regulate the temperatures. They will retain heat from the sun during the day and release it at night when air temperatures fall.

Once you have made/sourced your container/ raised bed, it is time to fill it with straw and manure, in layers. These carbon rich and nitrogen rich materials will break down in exactly the same way as the ingredients in your compost heap.

Simply add a layer of potting soil/ compost on top of your composting materials, water well, and plant up your beds, covering them to retain the heat as required.