How To Make A Hotbed To Grow Food Through Winter

Making a hotbed for winter growing is a great way to extend the growing season. It allows you to grow more, both towards the end of the year and early next year.

You can create this simple project for little cost, using materials from your garden and other materials you can source easily (sometimes for free) in your area.

Why Grow Food in Winter?

Since it’s so much more effort to grow food during the winter months than the summer months, you may be asking yourself – why bother?

No matter how organized you are over the summer, you’re unlikely to be able to can, preserve, or freeze enough food to sustain you all winter long.

By the end of winter, many of the root crops and other items you’ve stored will begin to lose their appeal.

You will use up some, while others may be past their prime.

By growing some fresh crops over the coldest months, you’ll be able to continue to eat well during the winter and get a jump on the next year’s growing season.

You’ll want to plant leafy greens, like these cold-hardy lettuces, and other crops you can graze on and harvest a little at a time over winter.

But don’t forget to add crops that will remain dormant over the coldest part of the year to give you a head start growing in the spring. Even in cold climates, there is a range of crops you can successfully overwinter to provide you with an earlier crop next year.

What is a Hotbed?

A hotbed is basically a raised bed filled with layers of decomposing straw and manure or other organic matter. You then add a thinner layer of growing medium (soil/compost) on top to grow plants or seeds.

Like any other compost heap, a hotbed is built up using organic materials. Ideally, there should be a good mix of nitrogen-rich ‘green’ and carbon-rich ‘brown’ materials.

Why Make a Hotbed?

A hotbed is one of a number of methods that can protect the crops that you grow during the coldest part of the year – through fall frosts and into winter.

By providing a source of gentle, natural heat, a hotbed is an alternative to more costly methods of winter heating.

It’s an effective measure to keep plants frost free – especially when used inside a greenhouse or polytunnel. Even when implemented outside, a hotbed can be covered by glass or plastic to retain the heat that is given off by the composting materials.

Keeping a cover over your hotbed will retain the heat and stave off frost.

It will also protect your plants from heavy precipitation, strong winds, and other winter excesses. What’s more, it will provide a level of protection against a range of pests that are a problem at this time of year.

Not only can a hotbed protect traditional overwintered plants, but it also provides some protection for tender or even exotic plants that typically can’t be grown where you live.

Finally, even when winter is almost over, a seedbed is still very useful. It gives an advantage to seedlings planted in cold areas in the first months of the year.

Where to place a seedbed

As mentioned above, a seedbed can be placed inside a covered garden structure such as a greenhouse, polytunnel or even a garden building or conservatory, or outside.

Where you decide to locate your seedbed will ultimately depend on where you live and local growing conditions. Of course, it also depends on the logistics of your location and the space available.

In a particularly cold region, it is a good idea to place the greenhouse in a covered area, as this can double its protection.

It is important to ensure that you do not place the greenhouse in a particularly windy location or in a frozen area.

If you live in an area with a much milder winter, this type of protection and care may be more than necessary. You can be more flexible when choosing a location for your seedbed.

When choosing a location for your hotbed, think carefully about the other features of your garden and how you normally move between them.

It is a good idea to locate your seedbed near your home.

In winter you don’t want to walk too far to check, harvest and care for your winter crops.

It is also more convenient if your greenhouse is close to material sources (i.e. compost pile and chicken coop, etc.).

One last thing to consider is proximity to a water source (ideally rainwater rather than tap water). The closer the water source is, the easier and more comfortable it will be to water winter plants.

Materials for a seedbed

Once you’ve chosen a location for your seedbed, it’s time to think about the methods and materials you’ll use to build it.

First, let’s look at the different options you can consider for the edges of your greenhouse. What you choose to fasten the materials to will obviously affect the heat retention capacity of the seedbed.

You can consider using:

  • Stone
  • Recovered bricks
  • Reclaimed concrete
  • Clay/adobe/cob
  • Recycled items: plastic containers, old drinking fountains, bathtubs, etc.

Or, for less permanent structures:

  • hay bales
  • reclaimed wood
  • natural wood/blocks

Building the edges of your seedbed

The process of building the edges of your greenhouse will obviously depend on the materials you use. However, the first phase will consist of collecting these materials. It may be useful to know how many of the materials you need.

Determine details:

To do this, you need to decide on the size and shape of your greenhouse, as well as its depth. For best results, the contents of your greenhouses should be at least 80 to 120 cm deep.

This gives you enough material to generate the necessary heat, as well as a top layer in which you can grow your plants or sow your seeds.

You may want to make the structures taller. This way you can grow seedlings under a cover supported by the edges of the bed.

Bed edge construction:

Once you’ve determined the size of your seedbed and gathered the edging materials you’ll need, it’s time to begin construction.

In my new seedbed, I used salvaged stones from our barn renovation, dry-stacked to create the edges of the bed.

The advantage of using reclaimed brick, stone or concrete is that these materials are excellent for storing heat because they have good thermal mass. They store heat and release it gently when the temperature drops.

Filling your seedbed

Traditionally, a seedbed is filled with horse manure and straw. Many Victorian/19th century greenhouses had beds made this way. However, it is not necessary to use horse manure or straw. Many different compostable materials can be used to create the same effect and generate heat.

Chicken manure and wood chips hotbed:

For example, when creating my seedbed I used:

  • chicken manure, from the chicken coop where we keep our 15 rescued chickens
  • partially composted chicken manure and litter (from the top of the compost pile near the chicken coop)
  • wood chips used in their nest boxes
  • other materials available, also wood chips, crushed remains from the forest garden and dried leaves.

I added these materials in thin layers, which encourages decomposition.

The key to sustainable growing systems is to use all the materials available in your garden and environment, and use what you have on hand.

Compress seedbed materials:

After adding the compostable materials, gently tamp the mixture to compress them. By compressing the materials, the heat generation capacity increases. You should aim to create a layer of material that, when compressed, is approximately 60 to 90 cm deep.

Supplement your hotbed with growing medium

After adding the compostable materials, cover the greenhouse with a mixture of soil and compost. I think a 1:1 mix is ideal. Ideally, the fertilizer should be homemade. But if you don’t already have your own compost, be sure to source and purchase a peat-free variety. (Using peat compost is terrible for the environment.)

The ratio between the heat-producing material and the growing medium should be 3:1, as this will achieve an ideal temperature of approximately 24 degrees C/73 degrees F. This is why you need a growing medium of soil and compost. should be about 20-30 cm deep.

Creating a cover for your hotbed

There are a number of different ways to cover your hotbed. For example, you could use:

  • An old glass window
  • A glass bell jar or mini greenhouse, or ‘hot box’ as they are sometimes called
  • Regenerated polycarbonate sheets
  • Plastic row cover or mini plastic polytunnel or greenhouse

To cover my hotbed, I used a glass pane reclaimed from the demolition of an old porch on our property.

The bed edges are slightly above the surface of the growing medium and the glass is placed directly on top of this. This is because I will be using the hotbed for seedlings, which will be pricked out and transplanted to other areas before they get very large.

Planting your hotbed

You will need to leave your hotbed for about a week to warm up. After this you can sow seeds or plant them directly. Numerous different seeds and plants will appreciate the gentle warmth that rises from your bed.
However, it is important to remember that this is not a permanent addition to your garden.

Within 2-3 months, the materials are largely composted and therefore no longer emit sufficient heat.

The future

But even though it will no longer be a hotbed, it is still a fertile raised bed. So you can continue to use it to grow your plants. You just need to make sure you continue to use new compost and liquid feed to maintain a nutrient-rich growing area.

Alternatively, consider removing the composted material and using the compost elsewhere in your garden, or removing just the fully composted top layers and supplementing with more compostable manure, straw etc. and growing medium.

A hotbed is a flexible and useful addition to your winter garden. So why not consider making one or two this fall? If you want to extend your growing season even further, we have 10 inexpensive ways to do so.

Stephanie Miles

I'm Stephanie, a passionate gardener enchanted by the magic of cultivation. My hands dance with soil, coaxing life from seeds to vibrant blooms. Amidst the symphony of rustling leaves and fragrant blossoms, I find solace and joy. From a single sprout to a thriving garden, my journey is a celebration of growth, resilience, and the simple wonders of nature. Join me in this green sanctuary, where every leaf whispers tales of life's beautiful simplicity.

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