Contrary to what one might think, issues with our plants tend to be caused by abiotic factors such as temperature, irrigation, and nutrient quantity, rather than an actual disease. The easiest way to determine whether your plant is experiencing a disease or abiotic issue is to look for a pattern in the affected plants.

• Abiotic issue – If plant stress symptoms are widespread, appear suddenly on multiple plant species, and do not spread further, then it is most likely an abiotic issue.
• Disease – If the plant stress symptoms follow a pattern (either random or specific, like ring patterns in grass), that only affects certain plants, and develops over time, then a disease is likely the cause.

Abiotic stress creates susceptible plant hosts for disease and insects, so recognizing the signs and creating the best conditions for your plant is the first step toward disease management.

Nutrients

Plants absorb light and carbon dioxide from the air, and water from the roots. However, in the soil, there are various nutrients a plant needs to function, similar to the vitamins we need. While light has a much larger impact on plant growth than soil, it is important to make sure your plants are in healthy soil. Nitrogen is an essential building block in proteins, in both plants and people. Phosphorus is used not just in DNA, but to help create energy for plants to use to complete their daily functions. Potassium helps plants complete various tasks such as transporting sugar, CO2 intake, and much more. There are several other nutrients plants need, and all of them serve critical roles in keeping plants healthy. In truth, light has a much larger impact on plant growth than soil, but it is important to make sure your plants are in healthy soil.

A plant at any given time can have the right amount of nutrients, not enough, or too much. The chart below explains what general signs to look out for if your plant is experiencing certain nutrient deficiencies or toxicity. Note that certain nutrient deficiencies/toxicities affect the abundance of other nutrients in the plant. (include pictures)

If you would like to learn more about plant nutrients and how to manage them, please use the resources below:

• NC State Extension Master Gardener volunteers of Wake County Gardening helpline
• Soil test
• NC State Plant Disease and Insect Clinic
• Extension Gardener Handbook: Soils and Nutrients

Weather

Both extreme heat and freeze events can stress and even kill your plants, especially a cold snap. It is important to know what type of extreme weather you may be facing, as well as how to care for your plants during these events.

Frost, Freezes, and Freeze Damage: There is a distinct difference between a frost and a freeze. A frost is when temperatures can reach as low as 32° F, however, the temperatures generally stay in the 30s.

Freeze/Frost damage typically occurs 24 hours after a freeze event, While freeze/frost damage occurs immediately, it’s still important to recognize the general long-term symptoms of freeze damage in plants. Examples of damage include bark splitting, floral blooms not developing, browning/dead tissue, blemishes on fruit, frost rings, or “cat nose” (triangular-shaped depression in fruit, common in peach and apple).

How to protect your plants from cold weather: Before considering freeze protection, keep in mind that most of the plants in your yard can tolerate cooler temperatures and have natural defense mechanisms. Woody plants shed dead tissue, and perennials/flowers from bulbs can regenerate from their roots. Any early blooming plants, certain edible crops, fruit trees, or container plants are more prone to freeze damage. There are a few simple ways to protect your plants from cold weather.

Location Matters: Where your plants are placed in your yard can improve or impair your plant’s cold hardiness. The best place to put your plants is the southern-facing side of your home because it gets more sunlight and is the warmest part of your home. If you live on a hill or have a deck/porch, keeping your plants at higher elevations will help, since cold air sinks and will be the most concentrated at the lowest point in your yard. You can simply move container plants into your garage or up against the southern-facing portion of your home during a freeze if you have the space.

If you can’t move your plants inside it is best to cover them until temperatures rise above 32 degrees Fahrenheit. Any insulating material, such as cover cloth or blankets is fine. If you do not have frost protection fabric make sure to add multiple layers and cover the plants down to the ground. You can use dry leaves or pine straw to cover small plants.

Water your plants thoroughly right before the freeze event as water retains heat. But be careful not to overwater, as soaked soil can increase root and crown rot disease prevalence. 

Drought and Heatwaves: On the opposite end of the weather spectrum, are droughts and heatwaves. As we all know, drought is the absence of rainfall for a prolonged period of time, and a heatwave is a period of abnormally hot weather lasting two days or more. Short-term effects of drought/heatwaves include older leaf drop, wilting, and leaf burn (browning along the edge of the leaf). Certain diseases, like anthracnose crown rot and phytophthora root rot, can also cause wilting, and other diseases can cause similar symptoms, so it’s important that you consider your environment when diagnosing your plants. If you see wilting and leaf drop immediately after or during warm weather, it is more likely to be a response to the heat, but if these symptoms occur regardless of temperature, there’s most likely a disease at work. Long-term effects of drought/heatwave include dieback, sunscald, decreased flower production, and poor pollination, which leads to decreased fruit production and smaller fruit. Because these symptoms take time to develop, it’s important that you protect your plants from the heat as soon as you notice these symptoms.

How to Protect Your Plants from Drought/Heatwaves: Protecting plants from the heat is much easier than protecting them from the cold, but some methods may surprise you. First and foremost, water your plants deeply AND infrequently. This encourages the plant’s roots to grow deeper, which can improve the plant’s drought tolerance. When watering, especially if you have container plants, water slowly. Watering quickly on dry soil can cause runoff, so let the soil absorb the water before adding more. The other key point in managing heat stress is not encouraging new growth. New growth causes plants to use more energy and resources, which makes them more stressed during a drought. Limit pruning to only dead branches/tissue and let your lawn go dormant. It’s not the prettiest sight, but it’s less stressful on your turf than forcing you to remain active with irrigation. For those with garden beds or container plants, the last step you can take is weeding, as weeds take away water from the plants you’re trying to grow.

If you would like to learn more about the impacts of weather on plants, check out the links below. Below you’ll also find links to our vegetable crop chart and Plant toolbox, to help you make sure you’re planting during the right season:

• Plant Toolbox
• NC Vegetables Planting Chart
• Interpreting Freeze/Frost Probabilities from the National Centers for Environmental Information
• Dealing with Drought
• Blueberry Freeze Damage and Protection Measures

Light and Space: While extreme environmental stressors like freezes and droughts are obvious events to protect your plants from, putting them in the right amount of light, space, and irrigation is crucial not only to disease prevalence but also to your plant’s overall health.

Light: All plants need a certain amount of light, and one of the most common mistakes in gardening is putting a plant where it gets less light than it needs. There are 4 general categories of light: full sun (6 or more hours of direct sunlight), Partial shade (direct sun only part of the day, 2-6 hours), Dappled Sun (shade through upper canopy all day) and Deep shade (less than 2 hours to no direct sun). While you might think putting a tomato in a spot that gets 5-6 hours of direct sun is alright, in this light condition it will never grow to look like how it looks on the tag. This is because the plant is not creating enough sugars throughout the day via photosynthesis. If a plant makes just as much sugar as it burns, it’s very difficult for it to grow or produce flowers/fruit. 96% of plant growth comes from sunlight, so putting it in the right spot is crucial.

Space: This is as straightforward as it sounds. Plants need space to grow. Plant labels indicate how tall/wide a plant gets, so putting a plant in a more compact space will limit its growth. Now, with plants like basil and marigolds, this isn’t necessarily a problem, as they and other plants can grow either in the ground or in containers just fine. However, for these and other plants that do better in the soil, it’s better to space them apart so that they can grow to their full potential. The thing to keep in mind is that plant growth can take years, so even though a garden is typically meant to look lush, it will take some time before the garden can reach that picturesque point. Putting several plants next to each other will not only prevent them from growing but also make it difficult for them to survive. As the plants adjust to being transplanted, they now have to compete with all their crammed-in neighbors. Not only that, but several plants squished together reduce airflow between the plants, which creates an ideal environment (in humid North Carolina) for fungal diseases to develop.

If you have any questions about any of these issues, please use the following resources:

• Extension Master Gardener volunteers of Wake County Gardening Helpline
• Soil Tests
• Be on the Lookout For (BOLO)
• Extension Gardener Handbook: Diagnostics
• Extension Gardener Handbook: Appendix C – Diagnostic Tables