Check your garden temperature before sowing (even after it finally gets warm!)

Posted by Jamie Oberdick on 04/03, 2013 at 01:29 PM

April is traditionally the time when most gardening really kicks off outside. While average last frost is still sometime in May depending on where you live in Central Pennsylvania, you can plant frost-hardy vegetables. Air temperatures, of course, are key for plants health and growth; but soil temperature is almost as important.

If you plant seeds on a warm day but the soil temperature isn’t suitable for germination, your seeds probably won’t sprout and could even rot in the ground and never germinate. Soil temperature warms slower than the air, and guides on seed packages cannot take into account that particular year’s spring weather. Or, in our case here in 2013, notable lack thereof. So, how do you know when to plant your seeds?

The best thing to do is invest in a good soil thermometer. They are not expensive and you can find them at most garden centers - call your favorite one to make sure. You stick them in the ground around two inches this time of year. As the sun grows stronger during spring, you will need to increase that to four inches or so to get a good, accurate reading. Don’t just do it once, do it several days in a row. Then get the average. If possible, do the reading at midday.

Okay, now that you have an accurate soil temperature reading, time to decide what you can plant. Google is your friend if you are not sure what you can plant at what temperatures. Let’s look at several scenarios:

- You get a reading of 40 degrees or more: In this case, you can plant things like peas, radishes, kale, arugula, spinach, fava beans, and a few of the Asian greens like tatsoi and pak choi.
- You get a reading of 50 degrees or more: Some Chinese cabbages, any alium (by that I mean onions, shallots, and leeks), rutabagas, turnips.
- You get a reading of 60 degrees or more: This is like just before last frost (sometime in May depending on where you live). So, you can now sow just about any vegetable that will not be killed by frost.

So, despite the cold winds outside, we are just about ready to start planting. I think after this long cold spell, everyone in Central Pennsylvania is ready to start sowing their local local food harvest. Just make sure the soil is ready.

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