Hot Bed and Cold Frame

Hot Bed and Cold Frame

It’s that time of year again. Every year around this time, I start wishing I had a greenhouse. I’m a little bit glad I haven’t built it yet, because I’ve decided to completely change the garden layout, and the greenhouse would have been quite in the way. But the problem remains: seedlings are stacking up and need to be moved outside to make way for more.

So, over the past three days, I built a hot bed and cold frame. It probably wouldn’t take you three days, because you probably don’t have a damaged nervous system… This is a simple set up that generates mild heat for a few weeks as well as trapping solar heat. It will hold several flats of seedlings, and when it has served its purpose for the season, there will be a nice pile of compost left behind.

First I arranged six bales of hay into a rectangle. This hay was on the ground row inside a haybarn, so it was a little ‘spoiled’ where it touched the ground. Price: free for the taking. Next, I layered cardboard across the bottom and a few inches up the sides – not a necessary step, but I had some, and thought I’d see if it made any difference. Then I placed a layer of spoiled hay, a layer of chicken manure, a layer of spoiled grass clippings from last fall, and a layer of shredded oak leaves, followed by a layer of compost and a final second layer of shredded oak leaves. The dark color of the final layer will draw heat, and as the other layers interact and break down, they will generate heat. (Horse manure is traditionally used for hot beds, but chicken manure works.) The surrounding hay bales act as insulation to hold the heat. The last step was to place a four foot wide by six foot-eight inch tall (long in this case) double pane glass door across the top, sealing in the heat.

This will need to be monitored daily to prevent too much heat build-up. When the weather is nice, I leave the glass door turned so that the four corners of the box ventilate. The warmer the weather, the more ventilation is needed. When the forecast calls for cold weather, I leave the box sealed. Pretty simple, but you do need a thermometer, and you do need to watch the weather forecasts religiously.

I’ve done this before, and let me tell you, those glass doors are tough! A few years ago when we had a hailstorm with some of the ice balls measuring two inches in diameter, I just knew the cold frame was shattered. But to my surprise, it was none the worse for wear. Last year a freak ice storm weighed down old trees to the breaking point. A large oak branch snapped and fell onto a stack of glass doors I’ve been collecting, and only the top pane of the top door was damaged – the other side was fine. I did at least learn not to keep glass under oak branches… but my point is, don’t be too afraid of hail damage (if you are using safety glass), and do build your cold frame out in the open.

Other notes… You could build the whole thing in a pit to help moderate temperatures even more, but you might have drainage issues, and that’s extra work. You could build it with the north end sloped higher to gain more solar energy and shed water faster – this is no extra work if you build on a south-facing slope. You can also line the inside of the cold frame with water-filled two liter soda bottles for thermal mass. This helps regulate temperature swings tremendously, but it does take up valuable space.

Try it. You’ll like it.

Seed Starting Time

February… It’s time to get serious about seed starting for the upcoming growing season. Onions should’ve/could’ve been started sooner, but I don’t mind buying sets (they’re cheap…) If you start seedlings too early, you run the risk of getting bored of babysitting plants for so long. They do keep growing and taking up more and more space, you know. That can be problematic if you are growing them in the house – which is why outdoor space is needed.

I wrote earlier about a greenhouse I’m trying to build. It turns out I’m in no condition to build it the way I’d like to… so I need make it even more rustic than I had planned (it will be little more than a small glass-covered pole barn.) In fact, I had planned to have it built by now. At least I’ve collected everything needed to build it. So, now the pressure is on - I’ve started some seeds, and soon I’ll start more, and soon they’ll need to be kicked out the door!

So, what are the other options for outdoor seedling storage? In the past, I’ve had good luck with cold frames. A glass door laid atop four bales of straw gives ample room for tall seedlings, and excellent protection from drastic temperature swings. But in February or even March, it just isn’t warm enough. My great-uncle tells me they used to build hotbeds for this situation. A hotbed is a cold frame set atop buried horse manure; as the manure decomposes, it releases heat. I haven’t tried this before, but it seems like a good idea. Gotta’ love those traditional solutions!

Another solution is the low-tunnel. This is basically a series of arcs covered with clear plastic. Water-filled bottles (thermal mass) lining the edges help moderate temperature swings. This works well for hardy plants, but still there is the problem of an actual heat source for frost tender plants. This is much less of a concern the closer you get to the LFD. Again, placing it over a hotbed would provide some heat. Low tunnels are excellent for protecting wide rows and getting a few weeks’ head start on the season.

So, if the greenhouse isn’t finished soon, there are simple alternatives. I’m only a few bales of straw and/or a couple wheelbarrows of manure away from a time-tested outdoor holding pen for the seedlings.

Let’s get back to those seedlings. I started artichokes, asparagus, cardoon, celery, and leeks a few days ago. Also, you need some fresh cut flowers in the summer, so I’m making my first attempt at growing Gerber daisies from seed. I found some old (8 years?) corn seed, and I’m germination-testing those to see if I can use them this spring. These will take anywhere from a few days to three weeks to germinate. I started them all by soaking in water overnight, assisted by bottom heat. Then I sow them in growing medium I mixed up from bulk materials (it’s much cheaper in the long run – I bought these materials last year – and you can tailor the formula for fussy seeds.) Then, I keep a lamp on below the flats and containers to keep the growing medium temperature around 64 Fahrenheit. With the exception of the corn I’m germ testing, these plants all need the longest time to grow before the Last Frost Date (LFD.)

Next on the list are eggplant, pepper, and tomato. I’ll be starting those soon. Peppers are the most difficult of the three to germinate, so they come first. Pepper seeds definitely need to be soaked for a day first and kept warm for several days in order to come to life. A splash of hydrogen peroxide in the water can help wake them up. Then come the eggplant seeds, because they need a few more weeks of early growth than tomatoes. Tomato seeds germinate easily and rapidly, and the seedlings only need six weeks, or as long as eight, before transplanting.

The bones of my indoor setup consist of an old houseplant storage ‘cabinet’ that I built from scrap materials twenty years ago. It wasn’t built specifically to the dimensions of seedling flats, but fortunately it works pretty well. It has three shelves that can hold four flats each, and I hang four-foot fluorescent lights over them. This has worked wonderfully since I started using it for its new purpose! And it doesn’t take up too much space. It is tucked neatly into a corner, with a south-facing window in the center.

This time of year is exciting and challenging. Getting seeds to germinate isn’t the only challenge; the real bear is the process of deciding which seeds to grow, and which ones have to stay in the personal seed bank for another year! Tough decisions…