If you want to get you seeds off to an early start you will need to create a nice warm and protected environment. There are 4 ways of doing this - soil warming cable, heated propagator, heating mat, hot press.
Early propagation requires a consistent soil temperature of 12ºC to 16ºC. Germination and root development are very slow below these temperature levels. If you have a large area to heat up then a soil warming cable is ideal. The cables are ready to use and can be plugged into a thermostat for complete temperature control.
You will need to build your own propagator – but this is relatively cheap and easy to do. The size of the propagator depends on the length of the cable. The following dimensions are recommended -
6m cable length - 50 watts 0.8m2 – 1.0 m2
10m cable length – 100 watts 1.6m2 – 2.0 m2
25m cable length – 320 watts 3.0m2 – 4.0 m2
- Make a wooden frame to sit on top of a sturdy shelf, adding a wooden base if needed. Use timber 10cm wide and 2.5cm thick. Line the sides and base with plastic, adding polystyrene underneath for extra heat conservation.
- Make you box the correct size to take the maximum number of propagation trays
- Fill the bottom 5cm with sharp or silver sand, available from builders’ merchants and garden centres. Do not use soft sand.
- Fill a 2.5cm layer of dry sand into the box and level it. Drill a hole into the wall of the box nearest to a socket. The hole should be big enough to feed the heating cable through. Stick the complete cable from outside through the hole. Lay soil warming cables in a series of ‘S’ bends, ensuring that the loops don’t touch (The cable could be plugged in immediately before this to make it soft and pliable). Fill another 1 – 1.5cm of sand over the cable or as much is needed to cover the cable. It should not be buried too deep. Level the sand carefully to achieve a smooth surface. The cable can now be plugged in. The heat will be distributed through the sand.
- When the propagator is in use keep the sand always moist (NOT WET)
- Push in a series of plastic tubes or stout wire to create a tunnel over the sand base. Secure plastic sheeting over the top to create a lid that can be adjusted by rolling up at the sides.
- Thermostat- To avoid overheating and electricity waste, a thermostat can be used to
regulate the temperature
- Tip: It is highly recommended to install a light source directly over the propagation box. Often propagation takes place in short days where there are not enough natural light hours to achieve healthy plant growth. With the help of a light tube (ideally ‘Grow Light’ tubes or similar lights for plant growth) and a plug-in timer the plants can be exposed to additional light hours. This will reduce the danger of ‘legginess’.
These are super easy to set up – like a mini polytunnel – and contain a heating mat 1.2m x 0.5m. They will fit on most greenhouse shelves and are easy to take apart and store when not in use. Can also be used to give a bit of protection to cuttings and delicate plants later on in the year. Heated propagators will ensure that your seeds have a constant steady temperature. This results in faster and even germination. Ideal for tomatoes, peppers, chillies, sweet peas etc. If you have an unheated greenhouse, then heated propagators will heat just the seed trays and you won’t face a bill for heating the whole room. You also don’t need to worry about fatal drops in room temperature if the propagator has a thermostat. Heated propagators also allow you to extend the sowing season. They can be used to help cuttings take and protect delicate plants later on in the year.
Like an electric blanket for your seed trays! The mat offers even heat distribution across a bench, and works best when placed on insulating material, such as polystyrene. It comes with a soil sensor and thermostat, and you can set the temperature up to 40 degrees C. It’s perfect for overwintering tender specimens, germinating seeds and taking cuttings. The aluminium mat is spray waterproof. The big advantage is that they can be set up and put away very quickly and can be used anywhere with light and power.
If you get all the towels out of the way this is a great place for starting off your seeds. Cover pots with a plastic bag so the soil doesn’t dry out. Good idea to put a sheet of newspaper down first - otherwise you will have soil everywhere!
Keep an eye out for germination and remove as soon as you see signs of growth. This is the big disadvantage of the hot press method as out of sight is out of mind – you could set a germination reminder on your ‘phone.
Have a look at our Propagation Section to view a wide variety of items which will help you successfully germinate your seeds.