7 Tomato-Growing Tips for Hot and Humid Climates
Growing tomatoes in hot and humid climates presents unique challenges. Join farmer Briana Yablonski to learn a few ways to grow healthy and productive tomatoes during muggy summer days.
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Tomatoes are some of the most prized jewels of the summer garden. There’s nothing like picking a ripe beefsteak and slicing it up for a sandwich or watching your kid pick cherry tomatoes with glee.
These plants grow best in the long, warm days of summer, but hot and humid conditions around tomatoes can lead to a few challenges.
When temperatures rise above 85°F (29°C) and humidity makes the air feel thick, tomatoes face greater disease pressure, struggle with fruit set, and often experience declines in overall plant health. Previously, this was primarily a concern for growers in the South, but a changing climate means more growers have to contend with extended periods of temperatures above 90°F coupled with high humidity.
We can’t change the outdoor growing environment, but we can take steps to help tomato plants survive these hot and humid periods. Here are a few tips to keep in mind.
Plant Early
Daytime temperatures above 85°F (29°C) and nighttime temperatures above 70°F (21°C) can cause blossom drop on tomato plants. When flowers fall from the plant, it can’t produce the juicy tomatoes you’ve been waiting for.
Planting your tomatoes earlier in the season is one way to avoid these hot, humid conditions around tomatoes during flowering. You should always wait until after the last frost to transplant tomatoes outdoors, but you may be able to plant them in early May rather than early June. If you see cold nights in the forecast, cover the recent transplants with row cover to help protect them.
Another option is to transplant a round of tomatoes during late July or early August. These plants will grow during some of the hottest days of the year, but the weather will cool by the time they form flowers. Plus, the new plants will be free from diseases that may have caused early losses in previous tomato crops.
Trellis Your Plants
Many detrimental tomato diseases are more likely to occur when it is hot and humid. While you can’t lower the humidity in the air, you can implement practices that increase airflow and keep moisture around the leaves low.
Tomatoes will grow into a mess of unruly, tangled vines if left to their own devices. These plants can still produce flowers and fruit, but the dense foliage makes harvesting difficult and limits airflow.
Trellising your plants keeps them off the ground, which offers two main benefits. First, it increases airflow around the foliage, decreasing the humidity. Second, it limits the likelihood that the foliage will become infected by soil-borne pathogens.
There are multiple ways to trellis tomatoes, and one isn’t necessarily better than the others. The number of plants, their growth habit, and your preferences all impact the right trellising method for you.
Avoid Overhead Irrigation
When humidity is already high, you want to do everything you can to keep the area around your tomato plants dry. Avoiding overhead irrigation is one of the easiest ways to do this.
Instead of turning on the sprinkler or spraying your plants with a hose, choose an irrigation method that applies water directly to the ground. Using a watering can or hose can still work well; just apply the water at the base of the plant rather than overhead. You can also install a soaker hose or drip irrigation system if you’re growing an entire row of plants.
Plant at the Proper Spacing
If you’re working with limited garden space, you may be tempted to avoid the spacing requirements on your seed packet. Rather than planting tomatoes 18 or 24 inches apart, you leave a foot between each one, hoping to enjoy a big harvest from a small space.
This close spacing may make sense on paper, but it can lead to detrimental results in reality. Packing tomatoes close together limits airflow and increases the likelihood that they’ll develop disease, a common issue for tomatoes in hot and humid climates. This close spacing also leads to greater competition for water and nutrients.
If you live in an area with high humidity, you should space your tomatoes at least two feet apart. The only exception to this is if you’re intensively pruning to a single or double leader. Although tight spacing may seem like it will lead to bigger harvests, it often leads to weaker, disease-prone tomatoes that yield little fruit.
Water Well
High temperatures cause water to quickly evaporate from the ground and increase rates of transpiration (that’s the plant equivalent of sweating). When you combine these two factors, it means you’ll need to water your tomatoes frequently during hot periods.
The exact amount of water you should supply depends on factors including size, soil type, wind, and humidity. High humidity lowers levels of evaporation and transpiration, but high heat still means tomatoes use a lot of water.
In most cases, you should supply your tomato plants with one to three inches of water a week. Remember, this is just a guideline, and you may need to water more. Checking the top few inches of soil with your finger is a good way to determine if you need to apply water: if the soil feels dry, it’s time to irrigate.
Save Water with Mulching
Mulching the ground around your tomatoes in hot and humid conditions limits evaporation and decreases the amount of water you need to apply. Straw, wood chips, and pine needles are all suitable mulches that will boost soil organic matter as they break down. You can also use reusable landscape fabric as a mulch.
Choose Disease-Resistant Varieties
Hot and humid conditions mean tomatoes are more likely to develop foliar diseases like early blight, Septoria leaf spot, and late blight. If you’re worried that these diseases will take out your harvest, look for varieties that are resistant to these pathogens.
Most seed companies will list which pathogens each cultivar is resistant to. Choosing varieties that harbor resistance to diseases you’ve dealt with in the past is always a good starting point.
If you’re struggling with soil-borne diseases, purchasing grafted tomatoes is a good option. These tomatoes consist of a disease-resistant rootstock and a scion that provides the tomatoes we love. The rootstock helps protect against pathogens like Fusarium wilt, bacterial wilt, and Verticillium wilt.
Prune Extra Foliage and Suckers
Remember how I said increased airflow is crucial during humid weather? Well, I’ll say it again!
Pruning suckers and leaves is one of the most reliable ways to increase airflow around your tomatoes. Removing the suckers, the shoots that appear in the elbow created by the main stem and leaf, will limit the overall size. While this may seem like it will reduce your harvests, it allows the plant to direct its energy towards the remaining flowers and fruits.
Even if you choose to forgo removing the suckers, you can remove extra foliage. I highly recommend removing the leaves within a foot of the ground to prevent soil from splashing onto the tomatoes. You can also remove any leaves that lie below the lowest cluster of fruits.
