What Temperature is too Hot to Fertilize Your Lawn?

Summer lawn care can be enjoyable or extremely tedious, depending on your climate and weather conditions. Regardless of whether you live in the temperate north or sunny south, chances are there will come a point in the summer when it is hot out. Letting grass grow longer and watering more frequently during summer heat are standard lawn techniques in hot weather, but what about fertilizing?

Fall and spring are generally the best times to drop granular fertilizer, especially for warm-season grasses that go dormant in the winter. Is it a good idea to spread lawn fertilizer during the summer heat? Read on to see exactly what’s too hot to use fertilizer in summer and how to protect your turf from heat damage. 

Is it Too Hot to Fertilize?

When air temperatures rise above 85 degrees, it’s generally too hot to drop fertilizer loads on your lawn. Warm-season grass that has plenty of water can handle a mid-summer, slow-release fertilizer to prepare for fall growth and impending winter dormancy. Sun intensity and wind conditions can also increase damage when using fertilizer in hot summer weather. 

When soil temperatures rise, cool-season grasses go dormant and focus on deep-root growth. This type of grass should not be fertilized after late spring as it will not absorb all the nitrogen. Excess nitrogen can spread to waterways and have a negative impact on the surrounding wildlife. 

Even summer grasses in drought-stressed turf will not be able to handle an application of fertilizer. Heat stress will prevent warm-season grasses from benefiting from a boost of fertilizer as unstressed turf would. A liquid fertilizer that helps water penetrate the soil and get to the roots faster can be used to revitalize stressed-out lawns assuming supplemental water can be added to achieve full green lushness. 

Why Can Summer Fertilizer be Harmful?

Fertilizing Lawn

Cool-season grass that turns brown in summer does not need organic fertilizers to bounce back. Instead, they do this naturally and will bounce back when the temperature falls again in the autumn. Even water-soluble fertilizers will not be taken up by grass roots on a dormant lawn. Summer grass types can sometimes use organic fertilizer to increase vigor but not if warm-season grasses are stressed from drought and heat.

Burnt TurfHot conditions and heat from fertilizerDead grass and brown spots
Summer Weed GrowthFaster nutrient uptakeWeeds outcompete turf grass
Higher Water DemandsWatering in fertilizerIncreases water usage and extra thirsty turf
Nutrient LeechPoor uptake by rootsPolluted waterways and weed growth

Burnt Turf

It is hard to keep grass blades green during the summer months, even with sun-loving varieties of grass. During summer months, it is important to protect the soil from direct sunlight, or dry soil might harm roots and kill grass in lawns. The increase in soil temperatures will be made greater if fertilizer is applied to a hot lawn and result in excess moisture loss.

Grass mixtures that have taller grass to shade the soil and lawn grass with deep grass root systems can survive drought better than one type of lawn grass. Bare spots and turf burn can lead to compaction, dead patches of grass, and prolific weed growth. Both cool-season and warm-season grass types should be protected from turf burn by withholding fertilization during drought-induced dormancy.

Summer Weed Growth

Dandelions and Lawn Weeds

During the summer, some weeds thrive in sandy dry conditions that result from periods of time without moisture. While the brutal summer heat beats down on turf grass, invasive weeds reach up and thrive in long periods of heat. By the time your lawn receives adequate moisture, the weeds will be taller than your turf and cause even more problems.

Avoid summer fertilization if your lawn is prone to hot-season weeds or you have bare spots that cannot be resown. If you need to fertilize your lawn before cold weather sets in, then wait until fall and use a post-emergent herbicide with fertilizer suited for your grass type based on the product label. Water thoroughly and re-seed before winter dormancy. 

Higher Water Demands

An actively growing quality grass will need much more water than a dormant type of turf. During the summer, you can keep some grass types lush and green and growing rapidly, but you will need to have ample fertilizer and abundant water. Increasingly turf watering restrictions during summer months are being put into place, and fertilization could cause problems if not watered in completely. 

If you fertilize grass with a granular type fertilizer application, you will need to add a lot of water to make sure it makes it down to the roots of the turf. In times of drought with no rain forecasted, you will need to use your home watering system to supply the correct amount of water. If ordinances restrict this, you may end up killing your lawn or causing other problems to your and neighboring properties.

Nutrient Leech

Nitrogen can only bind to the soil if the proper conditions are met. Slow-release fertilizers rely on nitrogen going into the soil and staying there, which requires time and ample moisture. Quick-release fertilizers need to be absorbed by plants right away, or nothing will hold them on your lawn. 

When too much nitrogen fertilizer is used on a lawn, then the grass can’t absorb it, and it runs off with watering. Dormant grass will not absorb any fertilizer as it is focused on using stored energy, not taking in new nutrients. Any nitrogen fertilizer applied to dormant grass in summer will be washed away and can damage water systems and wildlife, as well as fertilize invasive weeds. 

How to Protect Your Plants?

Milorganite 32 lb. Slow-Release Nitrogen Fertilizer

If you will be fertilizing in the summer, there are a few things you can do to protect your lawn and plants from heat damage. Making sure you have the right grass and live in the right climate to fertilize in the summer is very important. I also like to make sure the weather is right for the task and that I will be able to see the job through before the grass is harmed.

Turf and Climate

Cool-season grasses in southern or transient climates should rarely ever receive summer fertilizer. Warm-season grasses that are not drought-damaged may be fertilized as needed, but only if temperatures will not exceed 85 degrees or the maximum temperature on the product label. Make sure to use the lower dosage on the fertilizer load range during summer to prevent turf burn and other unintentional issues. 

Current and Upcoming Weather Conditions

Hot days with full sun are hard for you to work in and hard for your grass to grow in. Placing fertilizer which naturally increases the temperature of the soil as it breaks down on already parched and overheated lawn grass, can be a recipe for disaster. It is best to apply fertilizer with a broadcast spreader on a cooler, overcast day when the lawn will have plenty of time to absorb the nutrients before facing blazing temperatures and scorching sunshine.

Moisture Allotment

After applying fertilizer, your lawn will be extra thirsty and need more frequent watering than usual. If your watering schedule is rigid, you will want to make sure that you apply the fertilizer when watering will happen later that day or the next morning at the latest. When watering, makes sure there is no runoff and that all of the fertilizer is absorbed by your lawn and not washed away through poor water management. 

Follow-up Maintenance 

Check to make sure the fertilizer has dissolved and hand water any browning or dying spots. Make sure to hand-pull any weeds along the edges of your property and around weed-prone areas of your lawn to reduce the number of invasive plants you will need to deal with in the fall. Keep inspecting the lawn until everything is green and vibrant and then continue your normal summer lawn care routine.