On the whole, tomatoes are easy to grow, even from seed. The difficult part is our complete inability to control weather extremes during our Southwest growing seasons. Like many herbs and vegetables, tomatoes are sensitive to high heat and cold. In my High Desert region (zone 6B) of New Mexico, I have to deal with both most summers. Like many of you, I live in a valley, and the average temperature swing from daytime high to nighttime low in a given day is 45 degrees. So, here are few tips for keeping tomatoes warm when it’s cold and cooler when it’s hot!
Why Does Temperature Matter?
When you look up climate or zone info before planting tomatoes, you can find lots of information about the best time to plant. Just be sure to check whether the information you find is from the East Coast (low desert gardeners already are used to adjusting planting and flowering time) or more specific to your region. Social media is full of posts about planting tomatoes in April around the country. That’s too early for me (our last frost date almost consistently hits around Mother’s Day) and way too late for those of you in the low desert.
But there’s more to tomato tenderness than avoiding frost at planting time. Here are a few problems caused by cold or heat:
- Even after danger of frost passes, a tomato getting daytime warmth and ready to flower might drop its blossoms when evening temperatures dip below 55 degrees.
- When temperatures hover around 90 degrees F (and/or above 75 degrees for evening lows), tomato flowers probably won’t pollinate. Before I knew that little fact, I blamed myself, and even the bees!
- Some varieties can take more heat or are made for short growing seasons.
Plant at the Right Time
Foremost, plant at the right time for your region. Check with local nurseries, master gardeners or cooperative extension offices and materials to identify average last frost and typical tomato planting times for your area. Be sure not to plant too early or too late (too late puts fruit production into hotter weeks or means less chance of fruit ripening in cooler Southwest regions).
Choose the Right Varieties
In my short growing season, I cannot get a large heirloom or beefsteak tomato to ripen; I would need a hot house. So through trial and error, I have found a cocktail tomato (large enough to slice for sandwiches), a paste tomato and several grape or cherry tomato varieties that work for me. Our favorite for the vegetable garden and containers is Renee’s Garden Candy (first photo above). There are plenty of short-season hybrids out there, so keep that in mind. In hot zones, you can choose varieties called Heatmaster, Solar Fire or Phoenix for better success.
Get Tomatoes Ready for Life Outdoors
Before planting your tomatoes in the ground, make sure they have acclimated to the heat, sun and wind. This is especially true if you start seeds inside. Most tomatoes from local nurseries have been exposed to the cold and some breeze, but probably are under a shaded cover. Gradually introduce your starter plant to breezes and sun, based on their past exposure, and increasing time outdoors a little each day, for up to a week with those raised indoors.
Plant Tomatoes in the Right Place
Make sure your tomatoes get plenty of sunshine, but adjust what “full sun” means when choosing a spot for your plants. In low deserts, give the plants filtered sun or light shade in the afternoon. If this is hard to do in your garden, you can plant most tomatoes in a container that you can move around (assuming it is not too heavy!) as the weather heats up or into shade on extremely hot days.
Protect Tomatoes from the Elements
Aside from a container or planting where natural shade occurs, there are other steps you can take to heat up or cool down your tomatoes. We warm the ground with a wall of water before planting and then surround starter tomatoes with 5-gallon buckets surrounded by a wall of water until temperatures warm a bit and the tomato shows steady growth. We use shade cloths to shade the plants when afternoon temperatures rise in summer.
Keep Tomatoes Watered in Peak Heat
Consistent watering (with a drip if possible) keeps tomatoes healthy. It is better to water consistently and in the morning before temperatures soar than to flood the plants with water on a really hot day. For one, the plant already is stressed. Second, heavy and inconsistent watering can cause tomatoes to crack. Notice the drip system in the wall of water photo above.
Finally, don’t blame yourself if your plants fail to produce as they should. There is only so much you can do to control Mother Nature, so just try a new strategy next year!