Knowing the right time to shield your tomato plants is key to protecting your harvest. Understanding exactly when to cover tomato plants can make the difference between a bountiful crop and a disappointing one. This guide provides clear, step-by-step instructions to help you make the best decisions for your garden.
Covering your plants is a simple but vital technique. It guards against unexpected cold snaps, harsh sun, and pest invasions. Let’s look at the specific situations that require protection.
When To Cover Tomato Plants
The primary reasons for covering tomatoes fall into three categories: temperature extremes, precipitation, and pests. Each scenario has its own timing and best practices.
To Protect From Frost And Cold Temperatures
Tomatoes are tender perennials that thrive in warm soil and air. They are highly susceptible to frost damage, which can kill plants outright. Covering is essential in two key cold-weather situations.
In Early Spring After Transplanting
When you first transplant seedlings outdoors, they are vulnerable. Nighttime temperatures below 50°F (10°C) can stunt growth. A cover provides a warmer microclimate.
- Cover plants in the evening if the forecast predicts temperatures below 50°F.
- Remove covers each morning once temperatures rise consistently above 50°F.
- Continue this practice until nighttime lows are reliably above 55°F.
During Unexpected Late Spring or Early Fall Frosts
Unexpected frosts are a major threat. A single frost event can end your season prematurely. Always monitor local frost advisories.
- Check your local weather forecast daily during risky seasons.
- If a frost warning is issued, cover your plants before dusk.
- Ensure the cover extends all the way to the ground to trap soil heat.
- Remove the cover by mid-morning the next day to prevent overheating.
To Shield From Heavy Rain And Hail
While tomatoes need water, heavy rain and hail can cause physical damage and spread disease. Excessive moisture leads to fungal issues like blight.
- Cover plants if a forecast predicts intense, driving rain or hail.
- Use a cover that is waterproof or highly water-resistant.
- Ensure the cover is well-supported so it doesn’t collapse onto plants.
- Remove covers promptly after the storm passes to allow for air circulation.
To Guard Against Excessive Sun And Heat
Intense summer sun can cause sunscald on fruits, leading to pale, leathery patches. Young transplants are also prone to wilting in extreme heat.
Use a lightweight, shade cloth (30-50% density) during peak heat waves. Drape it over supports during the hottest part of the day, typically from late morning to mid-afternoon. This practice is especially important for newly transplanted seedlings.
To Deter Birds And Insects
Birds may peck at ripe fruit, and insects like hornworms can decimate foliage. Physical barriers are an effective, chemical-free solution.
Row covers made of fine mesh are excellent for this. Install them as soon as you notice pest activity or when fruit begins to ripen. Secure the edges tightly with soil or stakes to prevent pests from entering underneath.
Choosing the Right Cover Material
Selecting the appropriate material is as important as the timing. The wrong cover can do more harm than good by trapping moisture or causing overheating.
Frost Blankets And Row Covers (Floating Row Covers)
These are lightweight, woven fabrics that allow light and water to penetrate. They provide 2-8°F of frost protection and are excellent for extending the season in spring and fall. They are reusable and can be draped directly over plants.
Plastic Sheeting
Clear or black plastic is effective for trapping heat but must be used with caution. It should never touch plant foliage, as it can cause burning or freeze damage. Always support plastic on hoops or frames and remove it quickly on sunny mornings to prevent cooking your plants.
Cloches And Hot Caps
These are individual covers for single plants, often made of plastic or glass. They are perfect for protecting new transplants. Remember to vent them on warm days by removing the cap or tipping them slightly to allow heat to escape.
Bed Sheets, Blankets, And Towels
In a pinch, household fabrics can provide emergency frost protection. They are heavier and may require support to prevent breaking stems. Use them only for overnight frost events and remove them promptly in the morning. Avoid using plastic tarps directly on plants.
Step-by-Step Guide to Covering Your Plants
Proper technique ensures your covers are effective and don’t damage your tomatoes.
Step 1: Prepare Your Plants
Water the soil around your plants in the late afternoon before a predicted cold night. Moist soil retains heat better than dry soil. Gently tie up any sprawling branches to make covering easier and prevent breakage.
Step 2: Install Supports
Whenever possible, use supports like tomato cages, garden hoops, or stakes to hold the cover away from the foliage. Direct contact can transfer cold to leaves or cause abrasion. For row covers, install hoops along the bed.
Step 3: Drape The Cover Securely
Drape your chosen material over the supports. Extend the cover all the way to the ground on all sides. This traps radiant heat rising from the soil, which is crucial for frost protection.
Step 4: Anchor The Cover
Secure the edges with soil, rocks, bricks, or landscape staples. Wind can easily whip away an unsecured cover, leaving plants exposed. Make sure there are no large gaps for heat to escape.
Step 5: Timely Removal
This is a critical step. Remove the cover once temperatures have risen above the danger point, usually by mid-morning. On sunny days, even cold days, the temperature under a cover can rise rapidly and stress plants. If using plastic, removal is especially urgent.
When NOT to Cover Tomato Plants
Covering at the wrong time can be detrimental. Avoid covering in these situations.
During Warm, Sunny Days Without Ventilation
A sealed cover on a sunny day can create oven-like conditions, literally cooking your plants. If you must leave a cover on for pest protection, ensure it is a breathable fabric and that the ends are open for airflow.
For Extended Periods In Wet Weather
Leaving a non-breathable cover on during rainy periods can create a humid, stagnant environment perfect for fungal diseases. If using plastic for rain protection, remove it as soon as the rain stops.
When Daytime Temperatures Are Consistently Warm
Once summer weather has settled with warm days and nights above 55°F, permanent covers are unnecessary and can inhibit pollination by keeping bees and wind away from flowers.
Regional Considerations and Timing
Your local climate dictates your covering schedule. Here’s a general guide based on USDA Hardiness Zones.
Cool Northern Climates (Zones 3-5)
The season is shorter with a higher risk of summer frosts. Be prepared to cover plants from transplanting in late May through early June, and again from late August through September. Using season-extending row covers is highly recommended.
Temperate Climates (Zones 6-7)
Transplant in mid to late April, with covers needed for occasional frosts through early May. Fall frosts typically arrive in October, so have covers ready by mid-September.
Warm Southern Climates (Zones 8-10)
The primary threat is often a late winter or early spring frost after planting. Covering may be needed in February or March. In very hot areas, shade cloth for summer sun protection becomes more important than frost covers.
Common Mistakes to Avoid
Even with good intentions, simple errors can reduce the effectiveness of your covering strategy.
- Using black plastic directly on leaves, which attracts and concentrates cold.
- Forgetting to remove covers in the morning, leading to heat stress.
- Not securing the edges, allowing cold air and pests to enter.
- Covering plants that are already wet from dew or rain, which can increase frost damage.
- Using materials that are too heavy and collapse the plant underneath.
FAQ Section
At What Temperature Should I Cover My Tomato Plants?
You should cover tomato plants when temperatures are forecast to drop below 50°F (10°C). For frost protection, cover them if the temperature will dip near or below 32°F (0°C). It’s better to err on the side of caution with young plants.
Can I Use Garbage Bags To Cover Tomatoes?
You can use plastic garbage bags in an emergency, but they are not ideal. They do not breath and can cause condensation that freezes on leaves. If you use them, support them well so they don’t touch the plant and remove them very early in the morning.
How Long Can I Leave Covers On Tomato Plants?
Covers should be left on only as long as the threat persists. For frost, this is typically overnight. For pest protection, lightweight row covers can be left on for longer periods but should be lifted periodically during flowering to allow for pollination if they are not insect-permeable.
Should I Cover My Tomato Plants When It Rains?
Covering during heavy, pounding rain or hail can prevent soil splash and fruit damage. However, use a breathable cover or remove it immediately after the rain stops to prevent high humidity around the plants, which encourages disease.
What Is The Best Cover For Tomato Plants In Spring?
A floating row cover (frost blanket) is often the best choice for spring. It provides mild frost protection, allows light and water through, and can be left on for several days if temperatures remain chilly. It also offers some protection from wind.
Mastering the timing for when to cover your tomato plants is a fundamental gardening skill. By paying attention to weather forecasts, understanding the specific threats to your plants, and choosing the right materials, you can effectively shield your crop. This proactive approach minimizes stress on your plants, leading to healthier growth and a more reliable harvest. Remember, the goal is to create a stable, protective environment that helps your tomatoes thrive through unpredictable weather. With this knowledge, you can confidently protect your garden’s investment.