Just because the birch buds are open and the leaves are the size of a squirrel’s ear, or larger, does not mean you can plant outdoors with impunity. Sure, the leaves signify we will finally be free of frosts for a few months, but it isn’t just air temperature that is in play. Your soils are probably too cold for most seeds to germinate properly.
Three things can happen when you try to germinate seeds in soil that is too cold. First, and most obvious, the seeds may not germinate at all.
Second, the seed might germinate, but it will take longer for seedlings to emerge. Take peas as an example, since this is a crop we plant early. At 41 degrees it can take 36 days for seedlings to emerge. Wait 9 more degrees and it will take only 13 days. At 68 degrees it takes just a week.
The third thing that can happen is the rate of growth may be slowed by soil that is too cool. You will get a plant, but it will be a stunted one.
OK you know where this is going. We cannot equate air temperature with soil temperature. The soil will absorb radiant heat, and retain it, at least longer than air does. So just how do you tell what the soil’s temp is and should you plant seeds?
The answer is — still — to get a specially designed soil thermometer. “Specially designed” surely sounds expensive, but what it means is the scale is calibrated to read lower temperatures than when cooking, which calls for much hotter temps. You can buy one from nurseries, hardware and box stores.
Will a meat thermometer work? It might, so go to the kitchen and check yours. You need to be able to measure between 35 to 90 degrees. Some cooking thermometers will show this range, but others won’t.
Once you have a thermometer, it is easy to place its probe. The seed packet will tell you the depth the seed needs to be planted. That is where you want to take the measurement.
Listen to the “Teaming with Microbes” podcast:
If you are with me, so far, here is where you may want to check out the internet for the rest of the information. Look for two kinds. The first tells you the ideal temperature range for any particular kind of seed. The second tells you how long it will take for a seed to germinate given a particular temperature.
A good site with both sets of information is the Oregon State University Extension Service. Incidentally, as a gardener, you should be using a search engine called Ecosia instead of Google or another, as Ecosia plants trees with its profits, millions of them.
Finally, a word about starts and when they should be transplanted. There is a need to acclimate anything green to the outdoor conditions. This is called “hardening off.” Indoor-grown plants will get sunburned and possibly bleach out if you don’t gradually expose them to the UV rays and winds outdoors. It takes about a week of slowly increasing exposure to sun and wind.
And starts need, at a minimum, the temp for ideal germination you will find on one of the charts for that kind of plant’s seed. If it is too cold the plants will die or live a stunted life.
Jeff’s Alaska Garden Calendar:
Alaska Botanical Garden: Plant sale kickoff Saturday, May 11 from 10 a.m.-4 p.m. Members only early access from 9- 10 a.m. Join! Check site for so much more.
Hoses: Get ‘em out. Repair them. Set up your system.