Hot boxes: Early sowing of vegetables
What is a hot bed? What kind of vegetables can I grow on a hot bed? Are there any drawbacks?
What is a hot bed?
Hot beds were very popular in Victorian times. Once set up, they can be used to grow salad crops in winter, get a head-start on seed sowing in the spring (by up to a month), and for growing melons and any of the cucurbitaceae family in the summer. A hot bed provides bottom heat, using manure rather than electricity as the heat source, thus speeding up plant growth of seedlings and tender plants.
- The heat source: Fresh strawy manure - in a layer 60-90cm deep (after treading). As the manure breaks down, it generates heat. Tread it down well to compact it, ensuring a more even release of heat.
- The growing medium: A mixture of top soil and garden compost (ratio of 1:1) - this is placed on top of the manure in a layer 20cm-30cm thick.
The hot bed can be as deep and as wide as you want, as long as the ratio of manure to growing medium is 3:1. If you do decide to make the hot bed deeper, temperatures may rise above the optimum (24C) and plants may be scorched. It can be cooled down by adding water or leaves and garden debris to the mixture. Check temperatures regularly with a thermometer.
A hot bed can be made in a greenhouse or outdoors. Provide insulation in the form of wooden sides (4 pallets) and a cover if outside.
Leave the hot bed for a week to warm up.
There are several methods of making a hot bed.
- In a cold frame (the lid is useful for conserving the heat).
- In a pit, 60cm (24in) deep.
- Stakes and 4 pallets on the ground to keep the materials and heat in (see drawing).
- In a greenhouse.
What can I sow?
Seed can be sown direct in the soil layer, or in trays placed on top. After building your hot bed in January, small seeded crops like salad and radish can be directly sown on a well-worked fine tilth. A head start can be made by sowing trays of peas, beans, turnip and autumn cauliflower for transplanting outside. Courgettes and marrows can be directly planted in to the bed April/May. Experiment with different organic crops and tell us how you get on.
As a hotbed will only last for up to 2 months - contents will have to be removed and replaced with fresh materials. However, the material on top will be well decomposed and can be used directly on the garden in the spring. The bottom layers may have to be composted again to mature.