K's Garden

Building a large garden on a budget

Electric Windowsill Propagator Monday 2 March 2009

Filed under: Uncategorized — kgarden @ 12:00 am

Normally I sow my seeds in pans (shallow pots).  They are about 4″ diameter, and smaller than seed trays, as usually I only want a few plants. Then I pop the pan in a resealable plastic bag, and leave it on the window ledge until the seeds germinate.

Trouble is that the house is not really warm enough for some things – Tomatoes, Peppers, Aubergines and so on want 20-24C, and our central heating thermostat is rarely set above 19C, and has a night time fall-back of 16C.

So I treated myself to an electric propagator (well, two actually, but I don’t think the DW has noticed yet!)

I looked at a thermostatically controlled model, but I’m not that fussed.  Just something to provide gentle heat.

I got a couple off eBay called the “Garland Super 7” they take 7 small seed trays, with clear plastic domes and little ventilators, and they run at less than 20 watts. Cost £29.95 each



So I got busy and sowed some seeds.  For quite a few things I only want 6 or 12 plants, so I sowed the trays half-and-half. I’m never sure about this … often when I come to prick-out I find that the lifting the earlier germinated plants disturbs the later ones which aren’t yet ready to be moved.  We’ll see.

Propagator Seeds Sown

Propagator Seeds Sown

I’ve got one of those cheap plastic-covered mini-greenhouses (well two actually, don’t tell the DW that either please!!) in the conservatory, and I put any trays that have germinated, and my recently pricked-out plants, in there during the day so they get some warmth and sunshine, but I bring them back in and put them on the propagator at night when the temperature drops.

Update 09 March 2009

I’ve now got lots of little seedlings growing on in their mini-trays. During the day I put these is a mini-greenhouse which is in my unheated conservatory, and I bring them in at night.  I expect the house is warm enough for them at night (i.e. they only really needed the extra heat to make them germinate), but I’ve been putting them on the propagator to keep them warm.

But I’ve got more seeds to germinate, so I’ve bough an extra set of 7 spare trays, and lids, so that I can sow more seeds. The existing trays which have germinated will have to do without the propagator heat from now on! I think it is debatable whether I need lids, or not. The lids could probably be left off the seedlings – I’ve been venting them during the day for a while, but the best price I could find was for a package of Trays & Lids, but they are sold separately.

Provide More Light

Once the seeds have germinated they need lots of light, otherwise they will stretch and lean towards whatever light there is – and will become so-called “leggy”.

Even on a windowsill, right next to the window, this is still a problem.

If you can carry the seed pots/trays out to an unheated greenhouse/conservatory during the day, and bring them in at night (and you won’t drop them / mix the labels up / or any of the other various pitfalls that that entails) then that has to be the best bet. The all-round light in a greenhouse/conservatory is SO much better than a windowsill.

If using a windowsill is your only option then you need a reflector behind the pots / trays so that the seedlings get some light from behind, as well as from the window. I use something I knocked up from an old cardboard box with some kitchen aluminium foil taped to it:

Windowsill Propagator Aluminium Foil Reflector

I used this for a couple of seasons and thought I had been very clever! However, it turns out that kitchen foil is a poor reflector of light, and you would be better off with something painted matt-white (a panel from an old kitchen [white] unit perhaps) or better still a flat piece of polystyrene (polystyrene has excellent light reflecting properties). If you want Top of The Range you can use Mylar sheet, but its really not worth the cost / hassle for the benefit you will get.

You may remember from Physics at school that the power of the light falls off as the square of the distance (the “inverse square law”) – so double the distance from the window and you quadruple the loss of light energy. Don’t put your seedlings on the dinning-room table in the middle of the room! get them as close to the window as you can.

Another option is to use artificial light. You can get fluorescent tubes in an array to put over the seedlings.

T5 Growing lights

T5 Growing lights

The lights need to be very close to the seedlings – and inch or two, but not close enough that any heat burns them. Again, the inverse-square law is important, go up from 2″ away to 4″ away and you have reduced the “power” of the light by four-times … and at a foot away all your are doing is wasting money on the energy to power the lights, very little will be available to the seedlings (there are lights that have better penetration into the canopy of taller plants, but that’s a separate problem to seedlings which are all the same height. If you are interested have a Google for Metal Halide growing lamps)

See also the Vegetable Patch 2009 page


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