Seeds and Propagation


Image of a young plant seedlingIt is often the case that one of the major reasons for wanting to grow plants indoors is to be able to cultivate them out of season. Getting hold of the desired seedling starts from your local gardening store or garden centre can be more difficult during these times, since these establishments tend to cater to the outdoor gardener, preparing seedlings at their most commercially-fruitful (excuse the unintended pun!) times of the year. So how do indoor gardeners get growing at other times of the year (like now for instance, in November)? One of the answers to this question is to start from seed.
Getting seeds to germinate is not always as easy as it sounds and it can almost be an art form in which experience is invaluable. However, it also helps to understand the science too. Plant seeds often germinate optimally in environmental conditions that are different from those of the average day. In general, seeds most often germinate maximally when moisture is abundant and at higher than normal temperatures, but seeds from different plant species can also differ in their environmental requirements for germination, so it helps to know the ideal conditions for your particular seeds.

Seed Propagators

So hopefully you should now have an idea of what conditions your seeds like best, but what’s the best way to give them what they want?  A seed propagator is often used to control these environmental variables (particularly temperature) in an attempt to provide the best conditions for seed germination. There are several types of seed propagators available to the average user, but they mostly all fall into one of four categories:
1. Unheated seed propagators
2. Heated seed propagators (NOT thermostatically-controlled)
3. Thermostatically-controlled seed propagators
4. Variable temperature-controlled seed propagators

1. Unheated seed propagators

These are glorified covered seed trays – the cover is usually made from a transparent plastic and is there to reduce drafts, helping to maintain the temperature inside the seed chamber at a slightly higher temperature than the surroundings. The cover also serves to reduce moisture evaporation from the plant chamber reducing the chance that the soil dries out too much and inhibits seedling growth. These propagators are the least expensive but need to be placed in areas of the home where temperatures are conducive to optimal seed germination.

2. Heated propagators

Image of the Garland Super 7 heated propagatorThese tend to be pretty much the same as the unheated seed propagators described in 1. above, but with a low heat output device such as a heat mat or an integrated heated tray placed underneath the seed containers. The heaters in these propagators run continously but give off heat at such a low level to only raise the temperature of the seed tray by a specified number of degrees above the ambient temperature. These propagators can be placed in cooler places within the home, but as with unheated propagators, the ambient (external) temperature has to be monitored and adjusted to achieve the desired propagator temperature.

The Garland series of heated propagators are particularly popular with the home user partly due to their aesthetically-pleasing appearance, but also because they work well too. The lower heated tray contains carbon fibre heating elements that heat the seed trays that sit atop it. The propagators tend to heat the soil to about 8oC above the ambient room temperature although there can be a couple of degrees variability across the surface of the heated tray (the centre being slightly warmer than the periphery). Although a small amount of heat is wasted since the heating tray is not covered, the unique design allows for greater flexibility when controlling the seed chamber humidity since each seed tray can be vented individually (using the red swivel tab located on the cover). Once the seedlings appear, the covers can be removed but the soil should then be monitored daily since they will dry out quickly if left on the heated tray.

Garland Series of Electric Propagators

Number of seed trays
Individual seed tray sizeHeated tray sizeWattage
Garland Trio Top

23cm x 17cm76cm x 18.5cm13W
Garland Fab 4

17cm x 10cm38.5cm x 24cm10W
Garland Super 7

17cm x 10cm76cm x 18.5cm13W

On a more personal note, using the Garland Fab 4 Electric Propagator, we have so far germinated a number of seeds successfully in a 19oC room (soil temperature measured to be 28-33oC) under 12 hours / day of LED or CFL lighting (see table below).

NB: Whether lighting had an effect on germination is debatable but an interesting observation was that first appearance of the all types of seedlings tested so far have occurred under LED lighting as opposed to under CFL lighting, but this was usually a difference of a matter of hours. In addition, some seedlings under LED lighting appeared after some of the seedlings under CFL lighting so it is too early to say whether the types of lighting makes a difference to seed germination.

Seedling Germination using Garland Fab 4 Electric Propagator

SeedsSuccess RateFirst appearance of seedlings
Luffa100%3 days
Cherry Tomato88%3 days
Cucumber75%2 days

Image of two Luffa seedlings in a heated propagatorLuffa seeds & Cucumber seeds – these were obtained from a friend in the Middle East who grows their own Luffa and Cucumber plants. The Luffa seeds have proven very robust with 100% of them germinating very quickly in the Garland Fab 4 propagator, albeit not all at the same time. The Cucumber seeds showed a similar level of success, growing strongly under LED lighting.

Image of four Cherry Tomato seedlings in a heated propagator trayCherry Tomato seeds – these were obtained from and have pretty much performed spectacularly. They are advertised as 40 seeds for a very competitive price, but in reality, you get something like a couple of hundred. I got the feeling that they just bunged a spoonful of them into the sachet without counting. In addition, they bundled in another separate sachet of Safflower seeds as a gift – a nice touch. Planting 8 of the cherry tomato seeds in the Garland Fab 4 propagator led to germination of 7 of them by the 4th day (with most of the seedlings appearing on the 3rd day). Since then they have grown strongly under LED lighting.

3. Thermostatically-controlled propagators

Image of the retail packaging of a thermostatically-controlled propagator from the company, StewartThese seed propagators automatically switch on and off as needed, maintaining a seed propagator within a range of temperatures (usually between 18-23oC). However, it is important to realize that, with these devices, propagator temperature can NOT be set by the user  – the temperature range is predefined at the factory. Placement of these seed propagators within the home is less important since the temperature is automatically adjusted relative to the ambient temperature, although the propagator will not cool itself if the ambient temperature rises above the set range.

4. Variable temperature-controlled propagators

These seed propagators, as the name suggests, are essentially thermostatically-controlled propagators which can be set by the user to maintain a specific temperature. The temperature can usually be raised as high as 28oC, which is useful for some seed types. Temperatures below normal household room temperatures can also be set, as long as the ambient (external) temperature is not higher than the target propagator temperature, for instance by placing it in an unheated space such as a garage. Placement of these seed propagators within the home is less important since the temperature is automatically adjusted relative to the ambient temperature.

 Posted by at 5:35 pm