Do I need a heater to overwinter my seedlings?

Hi everyone, I have some flower seedlings & young plants that I am planning to keep in my greenhouse until after spring as well as my many new strawberry plants I managed to create from the runners, I was wondering if it is necessary to have a small heater in it? Or does the glass alone offer enough shelter & heat for them to survive the cold? It's double glazed (my dad made it from an old porch) so I'm sure they'd have quite a bit of protection as it is, however, I just wanted to make sure whether or not there would be much benefit from additional heat? Thanks.

 

It depends what you have out there Freedom Spark. Heat costs money and you may well get away without it. Your strawberries will certainly be fine. Mine will be out in the ground all winter.
If your seedlings and young plants are hardy they will be fine in the greenhouse without heat. If it's very cold or frosty you can drape a bit of fleece over them. It can stay on for days no problem.
If you tell us what kind of plants you have we can advise you better.

 

I have some lupins, hollyhocks, poppies - victoria louise, oase & papaver venus, globe thistles & delphinium - giant imperial, shasta daisy & gaillardia. I've also saved seeds from my own violas & Lychnis coronaria, they've only recently germinated. I was also hoping to sow some seeds in January in the green house - red hot poker for example. Thanks for the advice.

 

I'm not sure about the Gailardia Freedom Spark, they might not be completely hardy, but all the rest should be fine. As for sowing in January, well just my opinion, but I would wait until February. There is a big difference in daylight and temperature and in my experience things get on so much better. You might get on better if you let the seeds germinate indoors then put them out into your unheated greenhouse with some fleece over them. Sometimes there is nothing to be gained by sowing too early. Seeds sown in March will get on better than seeds sown in January. The only thing I would sow so early is chillies and peppers - indoors.

 

Thanks, so if I cover the plants with some fleece if the weather gets particularly cold they should be fine? I can just move the gailardia indoors during cold spells, if the rest are quite hardy a heater may be a waste of time & money. Thanks again for the advice Alice.

 

Hi,

It isn't so much the temperature, it's the damp that causes most of the problems I have in my greenhouse-and lower light levels.

I am going to try a couple of those silica gels boxes you can buy-usually from pundstretcher or somewhere like that.

I lose a lot because of the low light and damp conditions.


I agree with Alice sowing in inhospitable conditions is a complete waste of time. Early sowing of some plants is necessary for me-but that's because of where I am situated-we have better springs and autumns than we do summers so I have to factor that in-my dahlias for instance are absolutely gorgeous at the moment, and my roses are exploding. I wouldn't advise you sow even in February-March is much more likely to produce successful seedlings-even later if you can get away with it

 

Things that will live outside anyway will be fine in the greenhouse.

There are three issues to my mind:

Damp - as Claire says.

Heat - some winter days can make the greenhouse hot, that can start the plants growing, don't want that too early - the lush growth will be killed by the cold. So open the vents on any mild / sunny days.

Cold - not really a problem for plants that would be happy outside, but there is the risk that the pots they are in allow their roots to become colder than they would be insulated by the soil. The pots get cooled on all sides, if you see what I mean. But the temperature in an unheated greenhouse will mostly be enough to prevent the soil in the pots actually freezing - but fleece, or some emergency heat, in really cold snaps may be necessary (or just bring them into the garage or somesuch for a few days)

 

I don't suppose you have tried these silica "damp-boxes" Kristen? I know you can get them for your car-I was figuring two maybe three would suffice?


If anyone else has tried them and found them of use I would be interested to know ( a fiver each! not made o'money lol).

 

I don`t think they will be too useful, plants transpire a fair bit of water and the humidiity is usually higher in winter so you will need to soak up a goodly amount. An electric dehumidifier probably wouldnt keep up on wet days

 

Probably right, I ain't paying for a dehumidifier though lol, have to think of some solution.

 

I would agree with Hex about silica gel crystals. They is so much moisture in the atmosphere that they would have no impact.

Freedom. Alice is right in that with the exception of the Gailardia, all the others are perfectly hardy.

On the general point of heating a greenhouse, it needn't be as expensive as you think if you just want it frost free. I overwinter a number of tender plants in both a summerhouse and a greenhouse. And the combined cost of keeping both frost free last winter was less than £5 in total. In both I had an electric heater, an external electronic thermostat, and a power consumption meter to measure the amount of energy used. Mind you the cost of the equiptment was more than £5 - but it will hopefully last a long time.

I only set my thermostat to keep a minimum of about 1C. If I had wanted it to be say 5C, it would probably cost three or four times as much. The reason it is so cheap, is that most nights the heater is never triggered to come on. And when it does come on it is only for a short time. By contrast, something like a parrafin heater has to be on all the time - just in case.

 

"something like a parrafin heater has to be on all the time"

Does a gas heater work off a thermostat? (Still have to burn a pilot light I expect)

 

They say that in a house with gas central heating 10% of the gas consumed is just the pilot light.

 

I don't have mains gas here, but I thought modern boilers didn't have a pilot light any more? Electronic ignition I suppose?

But I've heard people say that they turn off their gas boiler for the summer for that reason, and use the immersion instead I suppose.

Actually, thinking about it, the pilot light doesn't matter in Winter - the heat is going into the house, and contributing to "warmth", so I suppose its only the Summer that matters.