Kitchen Garden Forum

I have just bought a heated propagator mat with the intention of using it on a windowsill to assist in germinating tomatoes, aubergines, etc. I already have several trays with lids which can be used with the mat.
I see that the heat is a constant 20C and that I should use a timer with it. My question is, how to set the timer so that i have a good steady heat 24 hours a day. Also, some seed packets for flowers say they should be germinated at 15C, so is 20C too hot, and did I waste my money on this mat?!? Any advice, please?
Thanks.

Hello Columbine

I'm by no means an expert so please take anything I say with a health warning. I would have thought that if your mat has an in-built thermostat you could simply leave it on all the time and let the thermostat turn it off if the temperature became raised during the day. If it doesn't have a thermostat then I would think that it might raise the temperature too high during the day if the sun shines through the window. If the room is at 20C then you wouldn't need the heating on at all so if it doesn't have a thermostat I think you will need to turn the heater off whenever the sun shines on the propagator. As I say, wiser heads may well disagree. If they do, they are probably right!

Regards

Ian

You can't keep it at 20C without a thermostat, but most things will germinate OK if you leave it on all night and turn it off on sunny days so you don't cook them.

I've been given a small propagator which is basically a heated tray with the little containers with lids. This also heats up to 20C like yours and has no thermostat, so I just need to keep an eye on it, make sure the compost doesn't dry out from the base too, and be ready to pot things up quickly once they have germinated.

It is useful for germinating small amounts of seed at a time on the windowsil, but would be better with a thermostat.

I've got a propagator with all the kit for precise heat control, a light, and a nice high cover in the greenhouse for serious growing though.

Thanks to Ian and to PlumPudding for your advice. My mat does not have a thermostat and that is why the instructions say to use a timer. So, taking your advice, I will leave it on all night and turn it off during the day. Fingers crossed!

Hello Columbine
I think that it would be a good idea to invest in a thermometer then you check temperatures. It is very difficult to estimate temperatures. A soil thermometer stuck in a sample pot of compost is needed.

John

Yes, John, I see your point about checking the soil temperature, and will look into getting an appropriate thermometer.
Thanks for your advice.
Columbine

Similar subject but slightly different question. I've got a heated propagator (Christmas present) which has a fixed temperature thermostat. It's in my greenhouse which I am keeping frost free but not warm. Compost in the seed trays which came with it is a fairly constant 25C. I've sown a few aubergine seeds because I believe they need a long season. I plan to sow some more later (end Feb?) and keep whichever turn out to be the best plants. They've not germinated yet (only been in a week) but I'm wondering what to do when the do germinate. I seem to remember reading somewhere that if I leave them in the propagator, even with the cover removed to increase light, they are likely to become leggy. It's too cold yet to leave them in the greenhouse without the propagator. The lowest air temperature about 6 inches above the propagator is varying between 10C and 15C. Obviously this increases if the sun comes out but the vents prevent it getting much above 20C (and of course the propagator's thermostat turns it off). I was thinking about making some sort of rack and putting the seedings on it above the propagator. I could even make the height above the propagator variable to get the right temperature. At 60Watts it isn't going to break the bank, unlike heating the whole greenhouse to that sort of temperature, which the other plants in there don't need anyway. I hope I've managed to explain what I mean. What views? If this isn't a good idea, what would you suggest? Perhaps I should just have waited a while before sowing the seeds!

Thanks

Ian

Get one of those growbag sized metalframe plastic covered "greenhouses" with wire shelves and put it in the greenhouse with the propagator on a low shelf.

Hey presto, hot propagator, warm plastic house, cooler greenhouse, plus easy access via full width zip m rollup door.

Peter

Good idea. I might try that.

Thanks

Ian

Just on lack of light - we have bought a kit this year that is a tray with a water reservoir which services the trays using capillary matting and has a canopy over the top with a couple of fluorescent lights fitted. We have added a timer to control the lights.

We have had problems in the past with leggy seedlings and it being too cold to get them into the greenhouse once they have germinated so hope this will be an answer. For us germination isn't a problem as it is usually warm enough in the house. The problem with light is that it isn't just the levels which are never as good inside the house - even on a window sill - but it is also the length of daylight hours when growing seeds early.

According to what other people have said we should also be able to grow salad greens during winter with it too. I'm charting our progress on our blog if anyone is interested.

I had such great hopes of my large heated propagator years ago, that it would produce early seedlings for me, but it totally failed to come up to expectations. Seedlings germinated too quickly, too early in the season and because of low light levels, invariably ended up being leggy and useless plants. I didn't have a greenhouse, and found that even 48 hours after germinating was sometimes too long a time to have left them in the propagator. By the time I'd taken them out, planted them on and left them on the windowsill, the light levels were too short in the day for them to develop into strong plants. I ended up giving the propagator away. with a greenhouse I might have managed a better compromise, but indoors on a bay window ledge, it just didn't work successfully.

Hello Primrose

So do you now direct sow outdoors only or do you raise seedings in your bay-window without a propagator? I'm trying with the propagator this year also in the gh without a propagator (later) and direct sowing (even later) as a not-very-scientific experiment. Some people tell me that they will all end up the same or even if there is a difference in harvest time it will be so little as not to be worth the effort, and electricity, to try for early plants. We shall see, but I guess that your location in the country, the particular location of your plot, the soil etc all have such an effect that comparison place to place is difficult.

First crocuses opened in my garden today. The daffs are only about 2" out of the ground which is really late but they will catch up. Maybe that supports the point about early and later sowing all ending up the same.

Regards

Ian

Plenty of people say that sowing too early is a great mistake, an that later sown stuff largely catches up.

I only partially agree with this. Certainly direct sowing early in spring can be disappointing, but for some things it is quite possible to sow too late as well. Greenhouse tomatoes and peppers benefit from a longer growing season - I'd rather have my first ripe tomatoes in June than green tomato chutney in November, thanks.

You do need some plan for growing the seedlings on, though. I use a 2' x 6' x 2' high "propagator" made of twinwall polycarbonate with a bubble wrap front, set on a bed of sand with a heating cable in it. They'll stay under there in 5" pots until late March, when the covers come off.

GL : As you might remember from my other posts, I have been raising plants using artificial lights for a few years now. At this time of year I have the lights on from 4 to 10 am and 4 to 10 pm (I did a lot of research including contacting the bulb manufacturer but couldn't find any timing advice). When the lights are on I cover the propagator with white painted insulation boards, I fondly imagine it keeps the light in as well as the heat. I am about to sow Aubergines and Tomatoes that will be kept in there as long as they will fit as well as Cabbage 'Primo', Cauliflower 'Snowball', Basil, Parsley and a mixed salad box that will only stay in until I start up the heated greenhouse in a couple of weeks. Covering the lights means I have not had a knock on the door from the Drugs Squad!

I have some growlights, and have used them some years, using timing much the same. The troubles I had were firstly, that for lights that are of modest power, they must be close to the plants - so when they are off they have to be moved to avoid blocking out the natural light, which seems a bother. The second thing that worrried me was whether any "weaning off" procedure was needed to avoid confusing them with an apparently shortening daylength ?

I like the idea of using that metalised bubble wrap insulation stuff as a reflector behind them to increase natural light levels. Must try it one year ...