Planting Tomato in Cold Soils

Q. I have some tomatoes and pepper plants in pots.  They are about 18" tall. Is it too early to plant them in my raised bed garden? It's been too cold lately to plant. 

A. You’re right, it’s been unusually cold. Both the air temperature and soil temperature are excessively cold for good plant growth of warm season plants like tomato and pepper. These are tropical plants, what we call “warm season”, and grow best at temperatures 60 – 65 ° F to about 95 ° F. They need enough new leaf, stem and root growth to get established and stay ahead of damage from disease or insects.

            How do you know if the soil temperature is warm enough? It is important that day temperatures are warm but nighttime soil temperatures can be cooler, down to about 45° F. A soil thermometer stuck several places in the soil, 1 to 2 inches deep for transplants, will give you a good idea of its temperature. I use an inexpensive AcuRite soil thermometer to do this.

            Garden soil, covered in plastic for a few days before planting, helps warm it up. The plastic should be sealed tightly against the soil. Then cut slits in the plastic where you plant. Covering the soil in plastic raises the soil temperature quickly. Covering the soil for 2 to 3 days is usually enough.

            I prefer tomato and pepper transplants to be about 6 to 8 inches tall when I put them in the ground. At this size they can handle a little bit of abuse and they are not so large they suffer from noticeable transplant shock after planting. Expect large plants like yours to go into a few days of shock before they start growing again. Warmer temperatures help them to recover faster.

            If plants are big, I pinch the tops back so the top and roots are in balance. It’s inevitable to have some root damage due to planting. Pinching the top back helps to compensate for this root damage.

            Transplant shock is an adjustment period the plant goes through when removed from a container and planted into a garden soil; from a protected environment in the nursery or greenhouse to a more hostile garden environment. All plants go through transplant shock. Smaller plants adapt quicker to a new environment than larger plants.