Saturday, April 18, 2009
Watch those soil temperatures!
Last year I tried to start my vegetable garden from seeds in April...and most of the seeds never germinated.. Well, I did some research on seeds and soil temperatures and found out that the soil temperatures were too cold last year, due to unusually cold spring temperatures. As you remember, last spring was terrible...in some ways the worst (coldest) since 1918. Here are some interesting soil temperature facts.
Most seeds have minimum temperatures that allow germination. And if the temps are close to those minima, germination can be slow or delayed. Some seeds like it cold (peas and parsley can germinate at 40F), while others need warmer temps (cucumber, eggplant and peppers like it hot...60F). My disaster was with beans (which like 50F). And you don't want to know about my tomatoes. So how can you determine the soil temps...well you can stick a thermometer in there (try about 1 inch in)...or there are web sites ...such as the Washington AgWeather network, controlled by WSU (see example above and the web link).
Right now the soil temp of the upper inch or so is approaching 50F in much of western Washington. Want to protect your seedlings and seeds from cold...add mulch. A few inches of mulch can greatly lessen the daily (diurnal temperature range). So it will take out the lows, but also lessen the highs. Cold air tends sink into hollows...so picking a higher location in your yard or even a raised bed can help. And soil temperatures are substantial higher with southern exposures...and particular on the south sides of buildings. Covering your plants with clear plastic..making a small greenhouse... really helps since the plastic lets the sun in, reduces the loss of infrared radiation to space, and lessens the amount of mixing out of warm surface air during the day.
Anyway, time for me to hit the nursery. But a warning...it will be warm on Sunday and Monday, but a cooling trend will develop Tuesday through Thursday. Too cool for tomatoes...which are notorious for being damage by cold. I have found some of the cold-favoring varieties really help.... cliff
PS: I will be at Costco in Kirkland from 11-1 PM signing their books
Posted by Cliff Mass at 1:43 PM