We talk a lot about getting your plants outside as soon as you can in the season. This has multiple benefits to the northern gardener. First, the sun is free energy and is far superior at growing plants compared to the artificial lighting we use. Second, if you can get your plants out sooner, it expands your indoor growing capabilities. We often start our hardening off processes 4 to 6 weeks before last frost, with a goal of having most of our plants outside for at least 2 to 5 weeks before we transplant into our gardens! This translates to mid-April to early May for us and our growing area.
We fully recognize that not everyone has the advantage of a temperature controlled greenhouse. That was us for many, many years. We pursued a number of different methods to inexpensively buy and build temporary greenhouses in those early days. In the comments, you will find a link for one such design we created, a fully climate controlled DIY seedling greenhouse! This design is fully capable of protecting your plants against temperatures in the teens and possibly even below, we tested ours down to about 12F.
We wanted to get this design out early as we recognize that acquiring parts and supplies in Alaska can sometimes take a bit of time, should you want to building something similar this year.
If you practice this early season extension technique, it’s important to only put your cold hardy plants out early in the season. You definitely don’t want to start with things like tomatoes and peppers, these are at risk of cooler temperatures! As always, before putting any seed grown plants outside, you’ll need to run your plants through a hardening off process. We’ll share our process a bit later, but it’s really quite important to do this.
When we were able to get a lot of our earliest plants outside sooner in the season, it nearly doubled our actual indoor growing capacity. It reduced the number of indoor grow lights we needed to use and also the amount of time we needed to use them. This was important for us as larger scale gardeners that grow everything from seed, but also can reverberate with others for many different reasons.
We’ve done some testing comparing electrical usage of heating a small greenhouse like this vs. grow lights. Perhaps shockingly, it’s considerably more economical to heat a small greenhouse like this than it is to run most indoor grow lighting! (Even highly efficient LED varieties!) And not by a small trivial amount, either.