Seeds and Propagation

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It 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.

Image of a young plant seedling

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

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.

Garland GAL44LSW self-watering propagator

Garland GAL44LSW 24 Cell Self-Watering Propagator

An unheated propagator popular with growers today is the self-watering Garland GAL44LSW 24 Cell Propagator. The Garland GAL44LSW is an ideal propagator for the less experienced grower who has a hard time getting seeds to germinate as a result of either overwatering their seeds or by not keeping the soil moist enough for them to take root. The Garland GAL44LSW propagator overcomes the need for judging how much water needs to be added for maximal seed germination by using a water reservoir and a capillary mat that wicks up the water into the seed-containing soil when it is needed. The propagator is also good for those who are not always able to keep a close daily eye on their growing setups (think allotments!) or are away for a number of days, as the water in the reservoir can self-water the soil for up to a week or two before it needs replenishing.

Quality-wise, the Garland GAL44LSW self-watering propagator is, for the most part, made of sturdy injection-moulded plastic, although the cover is much thinner and even a bit on the flimsy side. In addition, the fitting of the cover to the main body is not as snug as one would have liked and consequently is liable to being blown off if used outside in windy weather.

A couple of users have noted that the Garland GAL44LSW propagator’s cover has a shallower depth to it than some growers prefer, meaning that seedlings only have limited headroom to grow before the lid has to be removed. However, good growing practice requires that seed chambers are vented once seedlings have sprouted and reached sufficient size, in order to reduce humidity and better facilitate plant transpiration, which in turn allows nutrients to be more efficiently transported up into plant leaves. Indeed, since the propagator is self-watering, growers need not worry as much about seedlings drying out once the cover has been removed, and only need to monitor the water level of the reservoir.

Overall the Garland GAL44LSW 24 cell self-watering propagator is an excellent economical seed propagator that works very well for a variety of different seeds and makes germinating seeds a lot less work-intensive while at same time going easy on the grower’s bank balance.

Heated propagators

Image of the Garland Super 7 heated propagator

Heated propagators 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 continuously 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. The heated propagator 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 of it. The Garland heated propagator tends to heat the soil to about 8℃ 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 it 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 ourselves, we have so far germinated a number of seeds successfully in a 19℃ room (soil temperature measured to be 28-33℃) under 12 hours / day of LED or CFL lighting or just with natural light.

NB: Whether lighting had an effect on germination is debatable but an interesting observation was that first appearance of 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. 

For some plants we further investigated the difference between using a unheated propagator versus a heated one on seed germination. Seeds from different plant species were incubated in identical conditions in one of two Garland Fab 4 electric propagators, one was kept switched off while the other switched on with both of them exposed to natural sunlight. Seeds were placed in organic Root Riot® grow cubes surrounded by inert clay pebbles (Hydroton) as physical support. They were observed over the course of two weeks in order to compare the difference heating makes on the time to seed germination.

Testing seed germination in Unheated vs Heated Garland Fab 4 propagators

Seedling Germination using Garland Fab 4 Electric Propagator
Success Rate
First Appearance
of Seedlings in
UNHEATED propagator
First Appearance
of Seedlings in
HEATED propagator
not tested
3 days
Cherry Tomato
not tested
3 days
not tested
2 days
Curly Kale
6 days
3 days
Luffa seedlings in a propagator

Luffa Seedlings

Luffa seeds & Cucumber seeds - these were obtained from friends in the Middle East who grow 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

Tomato seedlings in a propagator pot

Cherry Tomato Seedlings

Cherry 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. We 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.

Curly Kale seedlings in a propagator pot

Curly Kale Seedlings

Curly Kale  seeds - these seeds were obtained from Amazon and have performed very well, germinating 100% of the time, even after two years of storage. As one might expect from any seeds, germination time was variable from individual to individual but the overall time that the majority of these Curly Kale seeds took to germinate was approximately halved by using a heated propagator. In these tests, Root Riot® organic starter cubes were used but these seeds are undoubtedly robust enough to be germinated in a range of different media. As for growth into adulthood, the seedlings grew strongly with some of them being transplanted to a hydroponics system for full-term growth in a conservatory where they also performed very well.

Thermostatically-controlled propagators

Image of the retail packaging of a thermostatically-controlled propagator from the company, Stewart

These seed propagators automatically switch on and off as needed, maintaining a seed propagator within a range of temperatures (usually between 18-23℃). However, it is important to realise 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.

Thermostatically-Controlled Propagators in the UK

Seed Tray SizeHeated Tray SizePower
Garland GAL40FT
23 x 17cm59.5 x 41cm50W
Garland Big 3
37 x 22cm80.5 x 41cm50W
Stewart Thermostatic 52cm
--52 x 42cm22W
Stewart Thermostatic 38cm
n/a38 x 24.5cm8W
-- Information not available

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 28℃, 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.

Seedling Germination using Garland Fab 4 Electric Propagator