Hotbeds
What are hotbeds?
The clue is definitely in the name when it comes to hotbeds. A hotbed is simply a surface or substrate that is warmer than its surroundings, creating a controllable or passive microclimate.
Why use hotbeds?
Hotbeds create an environment that will allow you to sow delicate plants such as tomatoes, cucumbers and peppers weeks or even months earlier than the season would normally allow.
Hotbeds will keep the growing environment at a constant optimal temperature for seeds to germinate faster and seedlings to grow throughout the season, even when the temperature drops overnight or during sudden, unexpected cold spells.
Hotbeds allow you to extend your growing season by weeks, or even months longer than seasonal temperatures would normally allow.
Types of hotbeds
Electric
A heating cable is used to heat a substrate such as a seed bed or damp sand on which seed trays and pots are placed.
Biological
A raised bed is filled with fresh manure and covered with compost. As the manure decomposes it heats up and warms the compost.
Fuel
A fuel such as wood, gas or oil is burned to produce heat which travels through pipes under a propagation bed.
NB:
We only have experience with electric hotbeds so the information given here is based on electric hotbeds, though much of the information is applicable to all heating sources.
When should you start sowing?
That depends on several things, such as the type of plants you want to grow, or whether you are relying on natural daylight or using artificial lights. Will you have enough room for the growing plants until they can be transplanted into their final positions? Will you be transplanting into a polytunnel or greenhouse or outdoors? We have been caught out a few times by a late spring and have struggled to keep plants healthy until the ambient air and soil temperatures were high enough and stable enough to plant out.
If you know the latest date of frost for your region you can work backwards from there. For example, how long will your seeds take to germinate and your seedlings to reach the size you want them to be when you transplant them.
What Can You Propagate On A Hotbed?
Any plants that need a temperature higher than the ambient temperature can be propagated on a hotbed. We generally use a hotbed for seeds such as tomato, cucumber, pepper, chilli and aubergine. Although the warmth is also good for germinating many other seeds such as beans, beets and brassicas etc.
When to remove your seedlings from a hotbed?
This will depend on the type of plant you are growing. For heat-loving plants there is no rush to move them on – the only requirement is to make sure the seedling roots and foliage have room to grow. Plants that require a cooler environment will need to be removed from the hotbed sooner.
Transplanting into larger pots
We use 144 module sowing trays as starters for most of our seeds except things like beans and squashes that require larger modules or even small pots.
With the optimum temperature, a good seed compost and plenty of light, it is surprising how rapidly your seedlings will grow so be prepared to transplant them into pots as soon as they develop a good root system.
Hardening Off
On a warm sunny day it’s easy to be fooled into thinking your seedlings can cope with being off the hotbed. But keep in mind how much the temperature can drop overnight. Even strong healthy seedlings can suffer from temperature shock if not hardened off properly. We generally start hardening our plants off about a week before we transplant them to their final location.
If all of the plants on your hotbed are to be transplanted at the same time then you can gradually reduce the temperature of the bed by a few degrees a day. If you have plants at different stages of growth then start removing the plants during the day and re-placing onto the hotbed at night, leaving off the bed for longer and longer periods each day until they are acclimated enough to be removed permanently from the bed and can be transplanted to their final position.
YouTube
We will be making a video on how we make our hotbeds soon which will be posted to our YouTube channel so please subscribe to our channel and newsletter so we can let you know when it’s uploaded and keep you updated on posts and new videos.