We are all watching our birch buds and comparing them to squirrels’ ears as noted last week. Those freak — were they? — showers didn’t help. And now I am sitting here watching two squirrels and imagining their ears are quite a bit bigger than they have been in previous years. Of course, they are not. Still, what a winter.
While we are looking above ground, waiting for that sign frosts are over for the season, we need to be looking at temperatures below ground as they are just as important. If the soil is not warm enough, you are not going to get any crops. And even if it is warm enough for seeds to germinate, performance will be greatly affected by the low soil temperatures.
The right soil temperature is needed to trigger germination. This process releases the specific bacteria and fungi carried by each seed. Unless the soil is at the right temperature, the soil food web that feeds the plant won’t operate optimally. You think you are speeding up things, but you are not. It takes longer for the plant to reach maturity and it won’t get enough nutrients until the soil warms.
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So we need warm soils, and they will come. They always do. Still, it doesn’t make any sense to waste growing days when you don’t have a lot to spare. We need to pay a bit of attention to what soil temperatures our crops need so we can get them into the outdoor soil as soon as possible.
Obviously, to do this you need to take the soil’s temperature and that requires a soil thermometer. You can buy one at a nursery or garden center. These are often sold as compost thermometers and sometimes have a ruler attached to take the temperature at a specific soil depth. You can also purchase a soil thermometer wherever they sell cooking utensils provided it registers down to 40 degrees. Last resort is to order one off the internet.
Next, you need to know what soil temperature each kind of seed requires. Sometimes packet labels list minimum, ideal and maximum soil temperatures. Yes, Alaskans, it sometimes gets too hot for some things to perform well. Ever wonder why spinach bolts when it gets warm? It doesn’t do great in soils warmer than 75 degrees.
There are lots of things that will germinate at a soil temp of 40 degrees — beets, cabbage, cauliflower, Swiss chard. Spinach and lettuces can even be germinated at soil temperatures just above freezing. For some reason, however, peas are always on the top of the list for early crops. They are a 40-degree crop, for sure.
You can use the best gardening tool you have, the internet, to look up planting temperatures. Suffice to say, crops can be divided into cool soil crops — peas, arugula, corn salad, endive, kale, mesclun greens, mibuna, mizuna, mustard, bok choy and parsley — and warm soil crops — beans, corn, cucumber, eggplant, melons, okra, peppers, summer squash, tomatoes, pumpkins and watermelon.
For many, the answer to not enough indoor space to grow transplant seedling is starting some of the earliest season crops, outdoors in pots. Then transplant them later, when you feel like it. Start with peas.
Cloches, usually, clear domes, are used to force plants like rhubarb — that box or bag over yours is sort of a cloche. They can also warm soil for early planting. Make your own soil warmer by turning over a large clay pot or set up a few “walls of water.” Or make your own tent-greenhouses.
Knowing the right soil temperature helps you know when to plant. Of course, we still need those squirrel-ear sized leaves, first.
Jeff’s Alaska Garden Calendar
Alaska Botanical Garden Plant Sale Kickoff: Members’ Early Access on Friday, May 12 from 4-7 p.m. Bring your membership card. Open to the general public Saturday, May 13 10 a.m.-4 p.m. Public sales on May 12 and 13 will take place in-person at the garden. Online plant sales will begin Monday, May 15.
10,000 free trees from Anchorage Audubon: Wow. White spruce seedlings to replace some of Anchorage’s tree loss! Visit www.mrwhitekeys.com/trees.html. (Yes, the wonderful Mr. Whitekeys!) Volunteers needed. Do check the website as there is an extensive distribution plan for late May. This is a very important effort and volunteer help is needed. Contact by emailing email@example.com.
Native Plant Month: The Alaska Native Plant Society has the info: Do check it out.
Seeds to plant outdoors in the soil: Peas, nasturtiums, chard, onion sets.
Sweep: If you do nothing else, just sweep up the driveway and walks a bit. It will look like you did some yardening.