When summer's heat is in full swing, you may be asking yourself, “Is it okay to fertilize plants in hot weather?” The answer is generally no. If a lawn, ornamental plants, or fruits and vegetables are drought and/or heat stressed, summer fertilizing can do more harm than good.
Don't fertilize plants or trees during hot summer months
An increase in growth means an increase in water and nutrient needs. During hot spells, it is especially hard to keep up with plant water and nutrient needs as soils dry out quickly and water may not be readily available.
Vital considerations for determining when it's too hot to apply fertilizer include avoiding fertilization when daytime temperatures consistently exceed 85-90°F (29-32°C), as high temperatures can stress the grass and increase the risk of fertilizer burn.
Applying fertilizer in the wrong season can cause increased tender new growth that can be damaged, especially if applied in cold weather in late fall or in winter. So it is best to stop fertilizing during dormant seasons. Additionally, in zones that can be in danger of a late freeze, it's best to wait until mid-spring.
Timing: Apply summer lawn fertilizer once between June and August, six to eight weeks after the late spring feeding.
You should take a break from feeding your plants during a heat wave or drought. However, to prepare them for conditions that could cause heat stress, regularly give them Miracle-Gro® Water Soluble All Purpose Plant Food (following all label directions) so they're nice and strong before the unfortunate weather arrives.
Late afternoon or early evening (when there's still light, of course) is the best time of day to apply lawn fertilizer. Applying it in the heat of a scorching afternoon can cause the sun's rays to burn your grass—and when your goal is "lush and green," burned grass blades simply won't cut it.
Perennials that require no fertilizer: Included are ornamental grasses, false indigo, ground covers, butterfly weed, bee balm, coneflowers, black-eyed Susans, sea holly, dianthus, asters and veronica.
Granular fertilizer needs the help of water for it to activate, so it will have no effect on your garden if you forget to water after adding it. For liquid fertilizer, you should wait longer before watering your plants. In fact, you can wait for as much as 12-24 hours to water your plants again for the best results.
Over- fertilization can lead to sudden plant growth with an insufficient root system to supply adequate water and nutrients to the plant. Poor root structure reduces the number of flowers and fruit production, and can result in plant growth spurts that won't be supported or sustained.
Ideal Storage Conditions
Cool & Dry Environment: Fertilizers should be stored in a cool, dry location. Excessive heat can degrade certain fertilizers over time, while moisture can cause clumping or even premature nutrient release, especially in granular products.
If you're not supposed to fertilize during heavy rains, you're also not supposed to fertilize on scorching days. During these days, lawns tend to lose their ability to retain moisture. When this happens, your lawn becomes drier and less able to absorb nutrients.
The ideal nutrient mix for summer fertilizers, such as 20-0-10, emphasizes high nitrogen and moderate potassium levels to support strong growth and water retention. Summer lawn stress signs include wilting, discoloration, and brittle blades, which indicate the need for adjusted watering and fertilization.
During extremely hot weather (daytime temperatures above 90F and nighttime temperatures above 70F), try to water daily or every other day. In a 10x10-foot garden, this would mean giving your plants 8 to 9 gallons of water each day.
The general answer is around 90 degrees F, with some exceptions to the rule. This means that when temps rise above 90 and remain there for a lengthy spell: Leaves wilt. Water evaporates into the atmosphere more quickly in high heat, draining a plant's reserves.
Factors That Affect Fertilization
Warm-season grasses, such as Bermuda, St. Augustine, and Zoysia, should be fertilized during early spring to early summer, just before the temperatures rise above 80ºF and peak growing season starts (late May to early July).
Some gardeners prefer to feed their flowers and plants with a liquid-soluble plant food once every one to two weeks. Some plants are heavy feeders and require regular fertilizing to thrive, while others will happily grow and produce for years with little to know fertilizer.
We recommend waiting 24 hours after fertilizing to water your lawn, which will give the fertilizer time to settle. After the 24 hours are up, it's important to give it a good soak—not just a quick spritz with your hose—to activate the fertilizer and help the critical nutrients absorb into the soil.
In general, fertilizers formulated for flowering plants would contain amounts of nitrogen less than or equal to the amounts of phosphorus (i.e. 10-10-10 or 5-10-5). This is because phosphorus encourages flowering. Too much nitrogen will stimulate green leafy growth at the expense of flower production.
Tender new growth is at risk of cold injury if it is forced late in the season, when plants and trees should be shutting down for winter. Plants and trees that have started hardening off are no longer concerned with actively growing, so fertilizing into fall is often not worth the effort.
Pinching. Pinch out the growing tip on flowering plants—annuals and perennials. When you remove the tip, the next set of buds on the stem awakens, and two new shoots start to grow. By pinching out the tip, you get twice as many growing stems, which means twice as many flowers.
Don't Fertilize
While fertilizer can be essential for healthy plants, extreme heat can cause them to be overstressed. While in this state, it won't be able to make use of the extra nutrients and the addition of them can add further stress which could end up killing it.
1. Nutrient Absorption and Grass Health. Fertilizing your lawn when the temperature is too low (below 50°F for cool-season grasses and below 70°F for warm-season grasses) can lead to poor nutrient absorption.
#1 Know When to Fertilize
The ideal time to fertilize such grass is once in early summer and again in late summer. If the grass in your lawn goes dormant during winter months, it is important to be sure the late summer fertilizer application occurs no later than August.