You want a lush, green lawn, but the summer sun is blazing. Knowing when is it too hot to fertilize lawn is key to avoiding damage. Applying fertilizer at the wrong time can harm your grass more than help it.
This guide explains the risks of summer feeding. It will help you understand the science behind grass stress. You’ll learn the best times to act and how to care for your lawn in extreme heat.
When Is It Too Hot To Fertilize Lawn
As a general rule, it is too hot to fertilize your lawn when daytime temperatures consistently exceed 85°F (29°C). During extreme summer heat, soil temperatures can soar much higher. This heat puts your grass into a state of dormancy or severe stress.
Fertilizing during this time forces new growth. This new growth demands water and nutrients the stressed roots cannot supply. The result is often burned grass, increased disease risk, and wasted product.
Why Heat and Fertilizer Are a Bad Mix
Think of your lawn like a person. In extreme heat, it focuses on basic survival, not on growing. Here’s what happens underground and above.
- Root Stress: High soil temperatures can actually damage grass roots. They slow down their function, making it hard to absorb water and nutrients effectively.
- Forced Growth: Fertilizer is a growth signal. It tells the grass blades to grow rapidly, but the struggling roots can’t support that demand.
- Moisture Loss: The new, tender growth triggered by fertilizer loses water faster. This worsens drought stress in an already tough environment.
- Burn Potential: The salts in fertilizer can draw moisture out of grass blades (desiccation) if not watered in immediately. In heat, this burning effect is magnified.
The Right Temperature Window for Fertilizing
Timing is everything in lawn care. The best times to fertilize are when grass is actively growing and conditions are mild.
For cool-season grasses (like Kentucky Bluegrass, Fescue, Ryegrass):
- Fertilize heavily in early fall.
- Apply a lighter feeding in late spring.
- Avoid fertilizing in peak summer (late June through August).
For warm-season grasses (like Bermuda, Zoysia, St. Augustine):
- Fertilize in late spring and early summer as they green up.
- Apply the last feeding by early to mid-summer.
- Do not fertilize in late summer or early fall, as this can hinder cold tolerance.
A good tip is to check soil temperature, not just air temperature. You can find inexpensive soil thermometers online. Once soil temps are consistently above 70°F, it’s a sign to stop fertilizing cool-season grasses.
What to Do Instead During a Heatwave
When it’s too hot to fertilize, shift your focus to protective care. Your goal is to reduce stress and help your lawn survive the tough conditions.
- Water Deeply and Infrequently: Water early in the morning (before 10 AM). Aim for about 1 inch of water per week, applied in one or two sessions. This encourages deep roots.
- Raise Your Mower Height: Let your grass grow taller. Set your mower to its highest setting. Longer blades shade the soil, keeping it cooler and reducing water evaporation.
- Sharpen Your Mower Blades: A clean cut heals faster. Dull blades tear the grass, creating larger wounds that lose more water and invite disease.
- Leave Grass Clippings: Let the clippings fall back onto the lawn. They act as a light mulch, helping to retain soil moisture and provide a tiny bit of nutrients as they decompose.
Spot-Treating Problems in Summer
You might see weeds or bare patches. It’s still okay to spot-treat weeds with a liquid herbicide, but be careful. Apply it on a cool, calm morning when temperatures are below 85°F. For bare spots, it’s better to wait for fall to reseed. Summer seeding often fails without constant, careful watering.
The Safe Summer Fertilizer Exception
There is one product category that can be used with caution in summer: slow-release or organic fertilizers. These products release nutrients very gradually over time.
They are less likely to cause a sudden growth spurt or burn. If you must feed in summer, a light application of an organic fertilizer like corn gluten meal or a slow-release synthetic product is the safer choice. But remember, the best practice is still to wait for cooler weather.
How to Prepare for Fall Fertilization
Use the summer months to plan for your most important feeding—the fall fertilization. This is especially critical for cool-season grasses.
- Test Your Soil: Send a soil sample to your local extension service. The report will tell you exactly what nutrients your lawn needs.
- Choose the Right Product: Based on your soil test, get a fertilizer with the correct N-P-K ratio. A higher first number (Nitrogen) is typical for fall.
- Mark Your Calendar: Plan to apply fall fertilizer when daytime temps are consistently in the 60s and 70s, usually around Labor Day in many regions.
This fall feeding encourages strong root growth, helps repair summer damage, and provides nutrient storage for a healthy green-up next spring.
Recognizing Fertilizer Burn and Heat Stress
If you’ve accidentally fertilized in the heat, or if a heatwave hits after an application, know the signs.
Fertilizer Burn: Looks like yellow or brown streaks, patches, or tips on grass blades shortly after application. It often follows the pattern of your spreader.
General Heat/Drought Stress: Grass has a bluish-gray tint. Footprints remain visible long after you walk on it. The soil is dry and hard.
If you see burn, water the area deeply and immediately to help dilute and move the fertilizer salts through the soil. This is your best chance to minimize the damage.
FAQ: Lawn Care in Extreme Heat
Q: Can I fertilize my lawn in 90 degree weather?
A: No, it is not recommended. Fertilizing in 90-degree weather puts immense stress on your lawn, increasing the risk of burn and disease. It’s best to wait.
Q: What temperature is too hot for lawn fertilizer?
A: When daytime temperatures consistently stay above 85°F, it’s considered too hot for standard fertilizer applications. Soil temperature is an even better indicator.
Q: Is it bad to fertilize grass in the summer?
A: For cool-season grasses, yes, it is generally bad. For warm-season grasses, early summer is okay, but late summer fertilization should be avoided to prevent winter injury.
Q: How do I keep my lawn green in extreme heat without fertilizer?
A> Focus on deep, infrequent watering, mowing high, and reducing foot traffic. A light application of iron (like iron sulfate) can sometimes enhance green color without promoting growth, but check if it’s suitable for your grass type first.
Q: When should I resume fertilizing after summer?
A> For cool-season lawns, resume with your main fall application when temperatures reliably cool down. For warm-season lawns, the last feeding should be done about 6-8 weeks before the first expected frost in your area.
Patience is crucial in summer lawn care. By holding off on fertilizer during extreme heat, you protect your lawn’s health. Your reward will be a stronger, more resilient lawn that recovers beautifully when the cooler days of autumn arrive.