Should I Plant my Tomatoes Yet?
By: Dean Gunderson
One of the most frequent questions we get this time of year is some variation of, “can I plant my tomatoes yet?” The answer is no! As a warm season crop tomatoes cannot tolerate any frost. Technically you can plant them as soon as the last frost, which is generally mid-April. However, we highly recommend you wait because soil temperatures, not just air temperatures, are critical to plant growth.
Tomatoes want warm soil temperatures, they are originally from the Amazon rainforest, they have no adaptation to cold soils. You generally want the soil temperature to be a minimum of 60 degrees, but they really do best when the soil temperatures are closer to 70 degrees. About a month ago the soil temperature was around 55 before quickly dropping to 33 degrees and then up to 60 before dropping back down and then started increasing again and is a little below 60 degrees in the first week of April. This last month shows just how quickly the soil temperatures can drop this time of year, so even though it’s close to 60 degrees now it’s still best to wait until temperatures are consistently warm.
If you don’t wait, and get the tomatoes in the ground too early, at best you get no benefit. When temperatures are too low tomatoes become stunted, stop growing, and if the low temperatures persist become nutrient deficient. Tomato roots struggle to absorb nutrients, particularly phosphorous, in low temperatures. The leaves gaining a purple hue is usually the easiest way to see a phosphorous deficiency.
So when do you plant tomatoes outside? We like to wait until early May. By this time we are far past our last frost date and there has been plenty of time for the soil to warm up. So even though you may see tomato seedlings at the store already, rest assured you are not late planting them and in fact you shouldn’t plant them for several more weeks.