13 Tips For Growing Tomatoes in Hot, Dry Desert Climates

Do you live in a desert climate and want to grow stellar tomatoes? Tomatoes can thrive in desert climates and yield abundant crops. Desert tomato growers may even enjoy plants with less disease, fungus and rot due to the dry climate.

However, desert growers are up against difficult conditions. Hot, dry days that drop down to very cold nights, low humidity and gusty winds, low water availability, and heavy monsoon rains. So how can you hope to have a great yield this season, if you live in a desert climate?

After ten years experience growing tomatoes and other veggies in the high desert of Arizona for farmers markets, I’ve picked up a few tips that can help you grow great tomatoes in hot, arid climates. This article will focus on tomatoes grown outdoors in soil or containers, not hydroponic or high tunnel-grown tomatoes.

Choose The Right Variety

Set yourself up for an abundant tomato harvest by picking a variety that will grow well in a tough desert climate. Most tomato varieties will grow in desert climates, but some will perform significantly better than others.

When choosing seeds or transplants, pick ones that are listed as “heat-tolerant.” Today’s tomato breeders are making excellent progress in varieties that can stand up to tough conditions.

Many super-tough tomato varieties are hybrid (F1) plants which combine the best traits of two parent plants. Hybrids have great disease resistance too. Hybrids seeds are not GMO seeds. The downsides of hybrid tomatoes are that the seeds will not “come true” to the tomato that you saved them from. The seeds also tend to be more expensive than open-pollinated seeds.

If you want to save your own tomato seed, choose an open-pollinated or heirloom variety. Red, pink, orange and yellow fruits fare better in the hot sun than dark-fruited varieties, which absorb more heat and are more prone to sunscald.

If you are only growing one tomato plant, you may have more success with smaller fruited types such as cherries or “saladettes.” These types tend to produce more abundant, consistent crops than larger fruited “big boy” types in desert climates.

Consider Virus Resistant Varieties

Curly-top viruses (CTV) are a family of pathogens that affect many crops including beets, tomatoes, bell peppers, and cucurbits in desert regions. Carried by the beet leafhopper insect as it migrates north in spring, some years are particularly worse than others.

The best thing a desert grower can do is choose CTV resistant varieties. In my years of growing tomatoes in Arizona, cherry tomatoes tend to be less susceptible than heavy-fruited heirlooms.

CTV symptoms show as a wilty-looking plant that fails to perk up even after watering. The wilty look gives way to a plant that may look stunted and twisted and fails to thrive, turning yellow and eventually brown. Unfortunately, there is no cure for CTV. The best course of action is to pull and dispose of suspected CTV plants immediately.

If you are starting your plants from seed you can choose seeds that are listed as Curly Top Virus Resistant, or CTV resistant. Ask your local nursery what varieties they have and if they are resistant to Curly Top Virus.

Know Your Last Frost Date

Part of the charm of the desert is the warm winter days. They can fool a gardener into setting out tender plants like tomatoes too early. However, desert winter nights can plummet to below freezing. This is especially true in higher mountain elevations and at the bottoms of deep canyons.

Before setting out tomatoes, know your average last frost date in the spring and watch the night temperatures judiciously through spring and early summer.

If the temperature even hovers above freezing, your specific microclimate (see below) may drop colder. Keep an old bed sheet or row cover handy in case freezing temperatures are predicted after you have planted tomatoes.

Observe Your Microclimate

Deserts have mesmerizingly varied terrain and vegetation that create unique microclimates. Daily and seasonal temperature swings can be extreme, due to the dry air which holds less moisture and warmth.

Microclimates can work in a gardener’s favor, such as a southern exposure in winter that warms earlier in spring. Trees that create dappled shade in the summer also impact your microclimate. Microclimates can also cause frustration, such as a low-lying garden where frost settles during spring long after other places are frost-free.

Observe the area you have available to grow your tomatoes. Ideally, it would be flat, but not the lowest point of the surrounding terrain, with good sun exposure. Cold air sinks, so the lowest points of your property are potentially the frostiest.

Heat banks such as large rocks can work in your favor in early spring to temper cold. But, they can also be scorchingly hot in summer. Access to a gentle breeze or air circulation is always good to reduce diseases. Breezy spots may also freeze last (depending on the type of frost).

Plant Extra Tomato Plants

You can always give away extra homegrown tomatoes, but the saddest gardening day is seeing your lone tomato plant die a premature death. Many things can happen – under-watering, over-watering, tomato hornworm decimation, gophers or animal damage, Curly Top Virus – so be prepared.

Plant one or two extra tomato plants. You can always prune them back if you are swimming in too much ripe fruit. Plants also enjoy each other’s company and help create a more humid microclimate amongst themselves.

Water Deeply When Soil is Dry

Deep, regular watering when the soil is dry down to the first knuckle is best practice for most crops in most climates, and tomatoes are no exception. Deep watering encourages deep root growth, rather than frequent, shallow watering which encourages lateral growth.

Test the soil for moisture by touch first rather than watering on a strict schedule. Water deeply, but don’t keep the soil saturated at all times. Plant roots need oxygen too, and water-logged soil has little oxygen.

Harvest Before Watering or Heavy Rain

Before you water deeply as mentioned above, harvest any tomatoes that are more than ⅔ ripe. The tomato flavor will be most concentrated when harvested from a plant in need of watering.

Most importantly, large amounts of water can cause hairline cracks in very ripe tomatoes, which drastically reduce their post-harvest life. Some large-fruited or thin-skinned varieties are more prone to cracking than others, so take this into consideration when choosing varieties to grow.

Add Compost to Increase Organic Matter

Soil organic matter is a gardener’s gold, it is where the complex soil web lives, decays and produces food for other plant life. Desert soils naturally tend to be low in organic matter, especially when compared with rich, dark soils of the midwestern United States. Desert soils can be extremely rocky, sandy, or heavy in clay which can make establishing a garden tricky.

Low organic matter does not have to be a death knell for your plants – amend with compost! If adding huge amounts of compost at one time is cost prohibitive, it is okay to build organic matter slowly over time (mulching helps build organic matter too).

Choose to amend only the immediate planting area with compost. If your garden soil is rock-hard or mostly dust, try building above-ground beds with soil and compost brought in.

Mulch the Soil Around the Plant

Mulching has been shown to conserve water, build organic matter in soils, and help even out extreme daily temperature swings. Wheat or oat straw is a widely available, relatively inexpensive mulch that works well for tomatoes. Other options include cardboard with wood chips on top, alfalfa hay.

Mulching may have the downside of encouraging slugs if the soil underneath stays wet constantly. Find a balance between mulching and watering, where the soil is not overly wet, and keep an eye out for slug damage.

Always avoid using bermuda grass hay for your garden or you may end up with an aggressive bermuda grass infestation.

Use Supports When Plants Are Small

Trellis systems or tomato cages are critical to keep your tomato plant from laying directly in the soil. Unsupported plants will easily pick up soil pathogens that cause disease and rotting fruit. There is no absolute right or wrong way to support a tomato plant, and you can get creative.

The best time to place a tomato cage or put in stakes for eventual trellising of your tomatoes is on planting day. If that is not possible, get your support system in before the plant is knee-high.

Waiting to trellis or place a tomato cage until the plant is large, branching, and even setting fruit will be a huge headache. Plus, working to lift up floppy tomato stems risks damaging the plant and knocking off green tomatoes.

If your trellis or cage is in place on planting day, you can prune it as needed as the plant grows into the trellis, making for a more manageable plant over the season.

Watch Out For Tomato Hornworms

Hornworms are a family of large caterpillars with conspicuous horns on their rumps, and the bane of gardeners around the country, even in the desert. 

Tomato hornworms (also called Tobacco Hornworms) are almost invisible when they are small, but give the babies two or three days of munching on your tomato plant and they will be as fat as your index finger. Hornworms can do a large amount of damage to the leaves and fruit very quickly.

Observe your plants closely, and learn to look for signs of hornworms – rough edged leaves, black or brown frass (poop) that looks like dust when small and is about the size of a peppercorn when from large caterpillars.

Try to catch the hornworms when they are small. Hand removal of the hornworms is the best non-chemical option, plus it is free and highly effective.

Harvest or Prune in the Morning

The best time to work in your plants is when the leaves are dry. This is true for pruning, harvesting, or adding more strings or supports to a trellis.

Working in wet plants spreads disease easily and is generally uncomfortable. Harvesting dew-covered tomatoes is wet and slippery work. Plus, the harvested fruits tend to have less robust flavor later as some of the water is absorbed through the skin.

The prime time to harvest tomatoes is in the morning after the sun has dried the dew, but before the tomato fruit starts to absorb the sun’s heat. Fortunately, morning dew tends to dry quickly in desert climates

Don’t Panic if Your Tomato is Not Setting Fruit

Your tomato plant is lush, thriving, and even flowering! You anticipate seeing green baby fruits soon, but after a while you still see no fruit. What could be wrong? First, don’t panic! Desert growers in particular are up against the most likely culprit: unfavorable daytime or nighttime temperatures.

Tomato fruit set is temperature sensitive, and does best with temps between 70 to 85 degrees. The blossoms will not set fruit if the day temps are very hot, especially if your days have been in the high 90s or 100s Fahrenheit. Likewise, fruit sets will not occur reliably with temperatures under 55 degrees, which could occur in desert nights even in the summer. In fact, day/night temperature swings between the 50s and 90s is common in the desert.

What can you do about this? Be patient. Tomatoes continually make new blossoms, and have the driving goal to reproduce fruit as much as you want to harvest homegrown tomatoes! Wait out the temperatures until they become more favorable, and keep observing.

The other option is to modify the growing microclimate for your tomatoes. This could take shape as adding shade cloth above the plants to reduce daytime heat. Be sure there is still good air flow to the plants. If the tomatoes are planted in containers, moving them into a more shaded area until the extreme heat passes could help cool down their microclimate.

Conversely, if night temps have been too cold, try covering the plants late in the day to conserve some of the heat and ward off cold overnight. You most likely would need to uncover the plants in the morning. This method adds one more “to-do” on your list, but should hopefully only last for a few nights, especially in summer.

Temperature fluctuations are the most likely reason for lack of or low fruit set on tomatoes. Other reasons include drought-stressed plants (increase water), or over fertilization with nitrogen (do not add any more fertilizer!) Most of all, do not panic and be patient. The tomato plant’s goal in life is to reproduce via delicious, beautiful fruit, so trust the plant is trying!