“When should I plant my tomatoes?” A common answer in central Iowa is “any time after Mother’s Day”. But does that rule of thumb still apply with this year’s cold spring? The best planting time for tomatoes depends on your weather conditions, but here are a few guidelines that can help you decide when to plant regardless of where you live.
The first thing to understand about planting tomatoes (and peppers and squash) is that they are warm weather plants. Tomatoes will not grow in temperatures are below 50 F. The first sign that it is warm enough to plant is the night time temperature stays consistently above 50 F.
The second thing to consider is the temperature of the soil about 4" deep. Ideally, tomatoes should be planted when the soil temperature is at least 60 F in the early morning. You can use a soil thermometer, a kitchen thermometer, or just stick your finger in the soil for a minute and see if it feels cold (if it feels uncomfortably cold it is probably below 60 F).
The third thing to consider is the weather forecast. Even if there have been a few warm days and nights and the soil temperature warms to 60 F, a forecast for significant cold weather indicates it may be better to wait to plant until warmer temperatures are in the forecast.
So where does my garden in central Iowa stand on these 3 considerations? Our night time low temperatures this week have been in the upper 30’s and 40’s. The soil temperature in my west-facing raised garden beds this morning was 45 F (the picture was taken in the evening when the soil had warmed, but it will be cold again tomorrow morning). The night time lows in the 10-day forecast has a mix of 30's, 40's, and 50's. All of that suggests I should wait another week or two, which puts us pretty close to….Mother’s Day.
*If you are wondering about peppers, add 5-10 degrees to the tomato temperatures to get the temperatures required for peppers.