Hotbed for Spring Seed Germination - Japan - ARI
by the Asian Rural Institute
page developed by Emma Marks, ARI intern from Wilmington College
submitted August 2019
Hotbed at ARI
https://gyazo.com/eee74a10d4657f4b108db40fa52ff8d7
A hotbed is a plant bed that relies on the warmth created by composting leaves to heat soil. At ARI, we build hot beds using local materials in order to extend our growing season. We build our hotbeds inside of greenhouses in early spring when outside temperatures are around 5°C. Once a hotbed is built, the soil can reach around 20-25°C. Then, we can start our seeds and transplant while the weather outside is still cold.
How we build hotbeds at ARI
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Prepare the bamboo. You will need 6 strong, thick pieces about 1.5 meters tall to make the main supports, 8 long thin pieces, and 8 short thin pieces.
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Drive the main supports into the earth
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Add the bamboo slats that will hold the straw sides
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The final structure should look like this.
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Fill the sides with straw, adding it in small bunches and packing it tightly.
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Once the sides are finished, it is time to start filling the hot bed.
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The main ingredient to fill the hotbed is leaves. We collect fallen leaves in the autumn and dry them. As the leaves decay inside the hot bed, heat is produced. You need a lot of leaves, so make sure you gather enough. If you do not have enough, you can mix some rice straw into the hotbed, but it does not work as well as leaves.
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We also add rice bran, which helps to stimulate micro-organism growth.
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A small amount of dried chicken manure can be mixed in if the hotbed will be used for plants that require a lot of nutrients (like eggplant). The chicken manure provides nitrogen and other nutrients, but if too much is added, it can harm the plants.
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Begin packing the hotbed with leaves.
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Once a layer has been added, soak the leaves thoroughly with water. The leaves need to be completely wet in order to start rotting and producing heat.
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Then, compact the layer by walking (or dancing!) on it. It's good to sing as well!
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Add rice bran while spraying with water.
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Continue adding layers of leaves, soaking with water, adding rice bran, and compacting until the hotbed is nearly full.
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Top the hotbed with soil that will become your planting material.
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Flatten and compact the soil
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Monitor the temperature of your hotbed. As the leaves ferment, it can reach 20 to 25°C.
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Trays of seedlings can be started in the hotbed even when the outside temperature is cold.
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The hotbed can be covered with a blanket to retain warmth
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Once the plants have reached a proper size, they can be transplanted directly into the hotbed.
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