Here is how I will be starting seeds in my hoop house in early March. Thought I would share as it is a very good method for winter sowing. Since heat rises, it is a good idea to store these mini pop bottle greenhouses up high. So the bottles are supported by the caps, at the top of the hoop house. I am also going to put some in the covered raised bed, but in this part of the greenhouse the temperatures can get well over 30 Celsius even in -10 Celsius weather, so I will have to be careful doing this. You could also use smaller water bottles for this as well. Eventually, the plastic will need to be recycled but in the meantime rather than just throw away your bottles to be recycled immediately, why not upcycle them for a few years of use right? I am also using rotten straw as a potting soil substitute, it works really well and I grow everything in straw from straw bales that have been conditioned with fertilizer to aid in composting. So no need to buy potting soil. You will have to ignore the condition of the seedlings in the picture, I planted those in November and they have been dormant all winter. Also, make sure you drill holes in the bottom of the bottles for drainage.
Just in case anyone is wondering, the bottles are cut around the bottom and the wire is holding them back together. The wire I used is a piece of steel tig welding wire, similar to that of a clothes hanger. which would also work. When you want to remove the plants, just remove the wire. To water, the plants just unscrew the bottle from the lid and use a bottle like a dish soap bottle to put water in there, or a spray bottle. These do not need to be watered very often especially in cold weather, I would say once every 2-3 weeks, in the winter even less.
I am hoping that March will have enough hours of sunlight in my region compared to February. As you can see in this picture, it is still pretty cold in the pop bottles to support healthy growth at this time of the month in February, which is also the coldest time of year in Ontario. It is -7C (20F) outside windchill of -13C (9F) but as you can see the pop bottles inside are 5.5C (42 F) just as the sun is setting (and I opened the greenhouse door a lot today which didn't help.). I think that as we get into March in Ontario and we see daily temps above freezing, this should provide enough warmth in the bottle to start seedlings. The only other issue would be available sunlight hours which I think will be good enough to start an early crop in the pop bottles and be able to move them to the raised bed about a month later.
Oh, the joy of living in Ontario. As you can see the nighttime shift in February temps even inside the hoop house, are no match for the freezing outdoor temps. I think the plan would be to start the seeds in the bottles, in the raised covered bed, and start the next batch of seeds in the bottles on the ceiling later in March. I really don't want to use a heat source for this hoop house, but I think the warmth of the hot composting straw in the raised bed will be enough heat to start seeds in March. I will just have to experiment and find out.
The day after we are having fairly overcast skies and the pop bottle suspended from the roof was only able to get to about 23F compared to over 40F yesterday. Outside temperatures are about 3F. I moved the pop bottle into the raised bed to see what the difference in temperature would be and it is about 10F-15F warmer in the raised bed than at the inside top half of the hoop house.
It is very cold today -20C, -4F, and the inside of the raised bed is -2C, 29F so This proves that with a bit more work towards insulating the north side of the hoop house and maybe sealing things up a bit better, I could keep the temperature of the raised bed above freezing without the use of a supplemental heating device. I was thinking of adding some high nitrogen fertilizer to the straw to see if the raised bed would get warmer from this, but I think watering the fertilizer into the bales would cause the temps to get colder inside the raised bed. I don't want to freeze the straw because this can take a long time to thaw even with some warm weather and would delay my ability to start seeds in cold weather in March.
Have you thought of adding a frost blanket to your covered raised bed? Just put it over the plastic that is already on the bed...it will help insulate it more. Some moisture in the straw is good if you want it to decompose slowly, but you're right too much moisture would be counterproductive - it would either heat up too much on warm days or cause things to rot/mold under the plastic without air circulating. It looks good to place the bottles in the straw also for insulation of the soil in the bottles.
Denise Cares wrote:Have you thought of adding a frost blanket to your covered raised bed? Just put it over the plastic that is already on the bed...it will help insulate it more. Some moisture in the straw is good if you want it to decompose slowly, but you're right too much moisture would be counterproductive - it would either heat up too much on warm days or cause things to rot/mold under the plastic without air circulating. It looks good to place the bottles in the straw also for insulation of the soil in the bottles.
I insulated with some cheap moving blanket around where the lid meets the top of the raised bed to reduce heat escaping from the inside. I also put a reflective space blanket on the top and some extra blankets to try and trap more heat in the raised bed during the day. I noticed that the straw in the raised bed is still moist and has not at all froze, unlike the straw I had directly on the ground inside the hoop house which did freeze almost solid. So this means that even at night the inside of the raised bed is still above freezing whereas the straw on the ground is freezing. I am also adding solar power to the greenhouse to aid in lighting so plants can grow even in shorter daylight periods in the winter.