How to Build a Hotbed Using Chicken Manure for Early Spring Planting

Cabin fever, some may say, is the restlessness of being confined indoors during winter. I get excited about the upcoming garden season and start making plans. When winter fully sets in and I see my barren garden outside, I cannot wait for warm weather. Since I own chickens, there’s always chicken poo to deal with, so why not use it to build a hotbed in late winter? 
A hotbed is defined as an earth bed heated by fermenting manure. As the chicken manure decomposes, bacteria break down the organic matter and release heat. This warmth allows us to start seeds earlier in the spring, especially in areas with colder winters. You can expect the temperature inside the hotbed to be about 5 – 10 degrees warmer than the outside.

Materials for Building a Hotbed

To start, let’s talk about different materials to build a hotbed. You can use various materials, salvaged or purchased, to build a hotbed, such as cinder blocks, wood, old windows, or greenhouse plastic for the lid. The possibilities are endless. In the planning stages, if you are using old windows, be sure to design the size of the bed around this.

Preparing the Manure Mixture

When sourcing the filling for the hotbed, be sure to use fresh manure from within the last couple of weeks. Older manure has already started to decompose and will not provide as much heat as fresh manure. It is very important to mix in other materials to ensure appropriate ventilation and a balanced composting material. Mix it with carbon-rich “brown” materials such as straw, shredded brushwood, or dried leaves for optimal heat production. 

Avoid using pine shavings as the high carbon content can hinder the growth of plants and beneficial microorganisms. It can also create anaerobic conditions that deplete the oxygen needed for soil and plant health. Pine shavings retain water that can create a swampy environment where mold and fungi thrive.

Steps to Build a Raised Hotbed

There are two main ways to build a hotbed: as a pit or as a raised bed. In this post, I’ll describe the raised bed method, which is what I use in my garden and is shown in the photos. For colder climates, a pit-style hotbed about 24 inches deep might provide better insulation, but for many gardeners, the raised bed method is sufficient and easier to manage.

1. Build the Frame: I used reclaimed wood to build a rectangular frame.
2. Add a Lid: I added a hinged lid covered with greenhouse plastic to hold in the heat. On warmer days, you may need to ventilate so it does not get too warm.
3. Fill with Manure Mixture: Build the manure layer high. More material equals more heat. I filled the frame with a mixture of fresh chicken manure and straw, about 16 inches deep, tamping it down and watering lightly.
4. Add Soil Layer: Monitor the temperature of the manure base over several days. Once the temperature has reached its peak, I added 6-8 inches of good-quality soil base for planting.

At the end of the garden season, your hotbed will be a decent bed of compost that can be rotated back to your garden. If you are looking for more information on hotbeds, be sure to search your County Extension website.