By Mark Barnes
It is always a gamble to put your plants in the ground too early in spring but taking certain precautions can pay off for a quicker harvest. Knowing when the average last freeze happens in your yard usually requires the services of an oracle, but we have some tips for you.
Although you might be eager to get an early start to your garden, tender plants can be damaged by a freeze, even a mild one. And when the weatherman says it will just get down in to the mid 30s, one still has to be careful or Jack Frost will make an early morning visit and wipe out lots of money you just spent on those expensive heirloom tomato plants.
There are four things you should consider when trying to up the schedule on your tomato or pepper plants. First, you need to know when to plant. Second, you should know where to plant in your yard. Third, you should know what plants you can get away with putting in early and, finally, how one should insulate those plants if you do plant them early.
So when should you plant? It really comes down to where you live. And, more specifically, what kind of microclimates you might have around your house. Those little nooks and corners of your yard can trap and keep just enough heat to keep a frost from settling down on your tomatoes. But by the time you figure out where those are, you are probably a gardener with enough experience to know when to plant.
Let’s look at the bigger picture for more novice gardeners. According to the USDA Gardening and Plant Hardiness Map for Idaho, Kuna’s last average frost date in spring is usually somewhere between May 21 and May 31. In the Melba area, which is a little lower in elevation, the last frost date is May 11-20. Be aware that in any given year you could have a last frost in early April, or even one as late as June. In 1978, the temperature in Kuna hit 31 degrees on May 25 and 30 degrees on May 31st. As recently as 2007, Kuna saw on May 28th a low temperature of 31 degrees. Melba, although usually warmer, has seen a freezing temperature in mid to late June. In 1995, the low temperature records were set for Melba on June 7 with a low of 29 degrees and just 13 days later it hit 32 degrees.
While these temperatures are barely below freezing, they can stunt the growth of hot weather plants such as peppers and severely damage newly sprouted seeds. The old wife’s tale of waiting until the snow is off the mountain, or after Mother’s Day works for some, but keeping an eye on the weather and planning ahead usually works better.
Next week, we’ll look at plants you can get away with planting early and how to get an early start to your garden. We’ll even give you some tips on how to protect those tender plants by using some simple materials around the house.
Mark Barnes is a former University of Idaho Extension Service Master Gardener.
If you have topics or suggestions about what to cover in this new column, please contact editor@KunaMelba.com.