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If there’s one thing we know about gardening, it’s that moisture is a critical component of the horticultural equation. Humidity — the presence and percentage of water vapor in the air — directly affects the moisture levels in your garden and can play a big part in the success (or failure) of your plants.
Humidity makes already-hot temperatures even more uncomfortable, but humid conditions also contribute to some tricky issues in the garden. Warm conditions are excellent for the growth of garden staples such as tomatoes and peppers, but when high humidity arrives, it can bring with it a host of other less-desirable visitors, such as molds and mildews.
The good news is that a period of hot, dry weather tends to halt or even end some plant diseases brought on by humidity. Therefore, if conditions cooperate, your struggles could be short-lived.
But if you live in a region with a penchant for high humidity, here are a few plant diseases to watch for, along with some suggested plants that are well-suited to life in a humid climate.
If you’ve been gardening for any length of time, you’ve most likely seen powdery mildew as it creeps surreptitiously through your garden, turning your lush vegetation dull, dusty, and powdery. Left unchecked, the powdery mildew wreaks havoc and can eventually kill the plants.
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This fungal disease is troublesome, but you can combat it with the right combination of tools and techniques. Start by using disease-resistant plants in your garden. Some heirlooms exhibit natural resistance to powdery mildew, so if this disease has caused trouble in your garden in the past, a switch to these cultivars could prove beneficial.
If you aren’t using disease-resistant plants, create more space around your plants to achieve maximum airflow, which can reduce the humidity around them. Also, try to always water around the base of the plants to avoid wet foliage. And if, despite your best efforts, powdery mildew does strike, remove diseased plants immediately to help stop the spread.
Blight the Blighter
Late blight fungus affects tomatoes and potatoes — members of the nightshade family — the spores forming when the relative humidity reaches levels over 90 percent, especially when combined with cool temperatures. The fungus results in lesions on leaves and fruit, spreads rapidly, and can quickly affect all of your plants. A strain of the pathogen that causes late blight is believed to have been the cause of the 19th century Irish Potato Famine.
Late blight targets tomatoes and potatoes, especially when humidity is high and temperatures are cool.
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Some people treat late blight with fungicides, but if you want to avoid using them and instead opt for more natural ways to avoid this fungus, choose disease-resistant cultivars, vigilantly observe your garden for early signs of the fungus, and plant as early as you can in the gardening season to avoid peak blight season during late summer.
It’s also important to rotate nightshades in the garden, so avoid planting tomatoes in the same location where you planted eggplant or potatoes last year.
Gray, Gray, Go Away
Fluctuating humidity levels can contribute to a flare-up of gray mold in the garden. Gray mold, also named Botrytis blight, is another fungus that you’ve most likely seen in your garden at one time or another, as it’s incredibly common. It generally manifests in the form of gray-brown spots on flower petals and leaves.
To help prevent gray mold in your garden, water plants early in the day, and give them space for air circulation.
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To curb the spread of gray mold, remove all diseased plant material from the garden. Take care to avoid wounding or damaging plants, as gray mold infestations tend to begin on weaker plants with injuries.
Controlling the humidity is one way to fight gray mold, but in lieu of controlling humidity, you can do what you can to improve conditions in your garden. Since mold thrives in hot, humid conditions, improve conditions by watering early in the day (from below, not from overhead), aim for ideal air circulation, and exercise careful pruning to prevent plant injury. It’s important to water from below, rather than pouring water onto the plant, to keep the leaves and plant as dry as possible. Organic fungicides can be effective against gray mold in some cases.
Downy in the Dumps?
Downy mildew affects roses, herbs, kale, and many other plants, and even though its name might lead you to believe otherwise, it’s not closely related to powdery mildew. The pathogens that cause downy mildew are influenced by high relative humidity, and they thrive in a wet environment. Due to the many types of downy mildew, it takes on several varying appearances, including lesions, spots, and fungal growth on leaves.
There are many types of downy mildew, and the disease may take the form of spots, legions, or fungus.
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To prevent downy mildew in humid climates, allow plenty of air space between plants so that air can circulate easily and help to dry wet leaves. This can be done at planting time as you set out the plants, or you can increase air space during the growing season by remaining vigilant about weeding and pruning.
When planting, situate your plants to take advantage of your prevailing winds, which increases air movement between your plants. Also, unlike plants affected by gray mold, don’t water your plants in the morning; wait until the afternoon to avoid exposing foliage to cool and moist conditions for prolonged periods. Removing diseased plants is another good way to help eradicate this garden disease.
All right, enough of the plant diseases. Let’s talk about something a little more fun: choosing plants! Maybe you can’t change where you live (and maybe you wouldn’t want to), but you can change what you plant in your garden.
Embrace your humid climate by packing your garden with plants that will thrive in your location.
Common bush or pole beans (Phaseolus vulgaris) aren’t always happy in hot, humid climates. If you’re looking for a better choice, opt for lima beans (Phaseolus lunatus), which are well-suited to a more humid lifestyle. (In fact, humidity can be beneficial to the overall success of lima beans.)
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‘Black Beauty’ eggplant is one of the more prominent eggplant cultivars, and it’s a proven choice for humid regions. It’s also incredibly beautiful!
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All you watermelon lovers, don’t miss out on growing ‘Blacktail Mountain’ watermelon. This classic heirloom has delighted gardeners for decades, and it happens to be a fine choice for growth in humid climates.
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In general, cucumbers handle heat and humidity well, but to increase the odds of success, trellis your cucumber plants. Trellising allows for a healthy amount of air circulation that can reduce your chances of developing powdery mildew. To avoid powdery mildew altogether, try ‘Platinum’ cucumbers, an open-pollinated cultivar developed at Cornell University specifically for its resistance to powdery mildew.
Okra is your friend, humid-climate gardener! Your garden simply won’t be complete without this warm-weather staple.
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If flowers are your fancy, wax begonias (Begonia semperflorens) are a smart choice. They handle humid conditions quite well and are intensely beautiful.
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Purple coneflowers make a spectacular addition to any garden, and they’re also tolerant of humidity.
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Don’t let the restrictions of a humid climate put a damper on your garden bliss! Learn to spot potential issues before they get out of hand, ensure as many elements are in your favor as you can, and fill your garden with plants that’ll appreciate your climate. And then walk out to the garden and enjoy every joyful, albeit humid, moment.
The Notable Nightshades
At first mention of the word, some might think of a poisonous flower, and others might picture a humble potato. Nightshades, or the Solanaceae, have a surprising amount of variety, and because of that, it’s one of the most important plant families on Earth.
More than 2,600 species claim Solanaceae as their family, including vines, shrubs, trees, and herbs. Some of the more popular plants, such as potatoes, tomatoes, and peppers, are staple foods for many around the world. Others hold a more infamous reputation, such as belladonna, a highly poisonous and potentially deadly plant.
Despite the wide range of nightshade plants, they do share some similar characteristics. Many of them sport simple alternate leaves, and showcase medium-sized flowers that grow in clusters. Notably, these plants contain a collection of compounds called tropane alkaloids. These compounds range from the soothing medicinal to the toxic pesticide, depending on usage and dosage.
Whether powered as a medicinal or rumored to be poisonous, nightshades have migrated worldwide and are closely woven into humankind’s past, present, and future.
Samantha Johnson is the author of several books, including The Beginner’s Guide to Vegetable Gardening, (Voyageur Press, 2013). She lives on a former dairy farm in northern Wisconsin with a Pembroke Welsh Corgi named Peaches and writes frequently about pets, gardening, and farm life.