Propagators and lights - Pros and Cons
Paula, Mill Pond Flower Farm
Most hobby gardeners start off their seeds and plants when the soil is warm enough for direct sowing, or by planting them in trays or posts on a warm windowsill. It works well and they get good crops of flowers and vegetables. There are also flower growers who sow direct into the field in late spring for summer blooming crops and in the autumn for overwintered annuals. However, sowing without heat can be unreliable, and direct sowing slow, subject to high attrition and weed competition.
Depending on your climate, it can mean that there is only space in the season for one crop of a flower. In the north of the UK, using only direct sowing would push the start of the season for annual flowers to late June if it was a kind Spring and mid-July if it was cold or wet.
Add heat to your growing set up, and the season can be extended significantly, but it does bring with it some drawbacks:
Setting up a propagator costs money – even a DIY sandbox requires some investment
Running a propagator costs money
A propagator takes up space, different models vary but they all need to be indoors
Plants in a propagator need regular attention – at least daily
Plants that have been germinated or propagated with heat cannot be planted straight outside so will need protected space to grow in
Too much heat without strong light leads to plants that are leggy and weak
Claire, Carol and myself all use heat for propagation through the winter and spring, although our set-ups are different. It allows us to start early in the season and bring on plants quickly for earlier flowers. I also sometimes have to use heat to germinate biennials, as Scottish summers can be less than warm. It took me a couple of seasons to figure out why I had such poor germination with biennials sown in modules outside. It was just not warm enough.
Types of propagator
There are a variety of different types of heated propagators, from the very simple, to high tech, very cheap to seriously expensive:
Heated room – my first seedlings for cut flowers were grown in an empty room heated by a radiator. It was fine for germinating seeds but there wasn’t enough light to grow them on. The whole room has to be kept at the right temperature so it’s not very efficient.
Heat mat/electric blanket – a heater element that goes under your seed tray and warms the compost from below.
Sand box – a box with lid and a heater cable buried in sand. The seed trays are placed on top of the sand and warmed by the cable. Heater cables are easy to obtain online and other elements of a sand box can be made from what you already have available.
Fixed/variable temperature propagators – a tray with a cover and heater element, plus thermostat to maintain a constant temperature
Mist propagation unit – a heater combined with humidity, often used for cuttings
Heated greenhouse
Grow lights can be added to all of the above
Germination unit – a heated stacker unit without light for germination of seeds only
Between us, we use a mixture of the above:
Claire – My bedroom has a radiator beneath the window, and lovely tiled windowsill, - not practical for keeping the room warm, but great for propagating. For 2 months from March-April, my husband sighs and pretends not to notice. I have a heated Vitapod in my garden greenhouse, where I do the rest of my propagating, and a windowsill in my study with a grow light, and a radiator below.
Paula – I’ve used windowsills, a heated room, and a sandbox. I now use a home-made heated germination unit, as detailed in the video. Seeds are moved into an unheated polytunnel as soon as they start to germinate.
Carol – I've got a mix of a Vitapod propagator and a home made electric blanket hot box, in the conservatory. Also a heated cable and sand bench in the cold greenhouse. This season, I am aiming to set up a new propagation tunnel with a heated sand bench, maybe with supplementary lighting if I feel I need it.
Getting the Best Results from Heated Propagation
Any space that requires additional resource, in terms of time or money, needs to provide clearly defined results in terms of more/better flowers. If you are investing in heated equipment you need to get the best from it and have it in use regularly.
Work from a seed sowing plan – don’t sow seeds before you need them and before you have the conditions to move them on.
Use fresh seed – you don’t want to waste compost, heat and time trying to grow stale seed and ending up with a half full tray.
Use good compost – find one you like and stick with it. You’ll learn how long it can be left in your propagator without watering, what it looks like when it’s dry and how it behaves. Seed compost is generally the only one I buy in and is worth it for reliable results. If you can source it, buy good quality peat free compost.
Fill your propagator – it’s not worth heating empty space.
When it’s full, open it as little as possible to maintain a stable environment and temperature.
Put seeds that need the same conditions in the propagator at the same time.
Know when your plants/seeds should be moved off heat to make sure they don’t get leggy and weak