grass in a boxI start most seed off in my greenhouse. I seem to get better germination and less slug and snail damage if I do this but I would really like a bit more heat in it to start things off even earlier. I don't have access to electricity in the greenhouse and nor do I want to pay a lot of money so what follows are a few things that I have tried and the solutions I have settled on.

The greenhouse in my garden does not have electricity in it or near it and it would not be practical to trail a wire or have it dug in so I needed to find other ways to heat it.  I had wondered about using a solar panel but there is nothing ready made and I didn't fancy fiddling around with panels, inverters and car batteries.

I came across one idea which I found on Sean's Allotment Garden Derby Lane 158.  This idea actually worked quite well and is good for keeping the greenhouse a little warmer overnight when it is going to be very cold. Tealights under terracotta pots. The tealights, I used 3, lasted for about 12 hours and the greenhouse was definitely warmer inside than outside. I placed mine on a slab on the floor so that the hot air rose.  I really wanted to place one under each set of shelves  but wondered if that was a bit too much so placed it in the middle of the greenhouse. Be very careful when picking up the pots after use though as they are very hot! I couldn't, however, see myself burning candles 24hrs a day even though they are very cheap. It is also not terribly safe even though my greenhouse is aluminium.

One thing I do have a lot of in my garden is stones, often quite big ones. It doesn't matter where in the borders I try to plant something, I always end up removing large stones not unlike Budleigh Buns but a bit murkier in colour.  I know these can get quite warm in the sun as I can feel that warmth when moving them from the borders if they have been lying on the surface.  I also used to have one strawberry plant on the allotment that had two large stones on either side of it and it produced way  more fruit earlier than the other plants.  So under the two front sets of shelving I have placed stones. As they are facing the sun, they will warm up when the sun shines in and then gently release the heat when it isn't.

An idea which turned up on several blogs was to have a large tub of water in the greenhouse. This warms up when the sun shines and releases the heat when it gets colder.  In fact, this works very well and I now have a large black dustbin of water in the green house on the sunny side. The greater the volume of water, the more stable the temperature. It does mean that I can't grow anything in that space but I would rather have a bit more heat when the sun is not shining than squeeze a few extra seedling boxes in.  This combined with the stones gently raises the temperature inside the green house.

Another material that I have a lot of in my garden is grass. We cut the lawn weekly and many years have to cut it all year round with no break between December and March.  I had heard about hot beds or boxes made with manure, Charles Dowding using one to start off his seedlings in the greenhouse. Most hotbeds are built with manure but I don't have any at home and don't want to buy it so have used grass cuttings instead.  The downside of using grass is that the box does not retain the heat for as long as manure but as we cut the grass so regularly, I always have some that I can use to rebuild the heap.

I use an old compost box made of wooden slats and a plastic lining inside at the bottom to keep the grass in one place. I then pack it down really well because the tighter it is packed, the longer it retains the heat. I then place boxes of seedlings directly on top of the grass. I did try using metal shelving on top of the box but the grass sinks down quite quickly and the seedlings were left a little high and dry.  If you pick the seedlings up, you can feel the heat on the bottom of the tray.  From February onwards, the grass has heated up to 70 degrees and will stay like that, slowly going down over 7 - 10 days. Just enough time for me to cut the grass again and refill it!

I don't fluff the grass up because it releases ammonia and that can burn the leaves of the seedlings. I also wait two days before I put the seedlings on the grass and then they are less likely to get damaged by ammonia as well.  

If I could only use one method, I would use the grass box as it targets the seedlings directly. I do use the stones and water to raise the temperature in the whole of the greenhouse and then the grass box for new sowings.

Do you have a free way of heating a greenhouse or polytunnel?