Managing Heat Stress in Idaho Gardens

          

As Idaho summer heats up and dries out, gardeners across the state are feeling it—wilting veggies, crispy lawns, and blooms that barely last a day. Even the best-tended gardens can struggle in a heatwave. Knowing the signs of heat stress and how to respond can help you keep things growing through the toughest stretch of summer.

What Is Heat Stress?

When temperatures climb high enough, plants can’t cool themselves efficiently through transpiration. Moisture evaporates faster than roots can replace it. To conserve water, plants close their stomata—but that slows growth, reduces yield, and weakens the plant. Long stretches of heat can cause real damage, and in some cases, even kill the plant.

Vegetable Gardens: First to Feel the Heat

Vegetables, especially those in full sun or shallow soils, are usually the first to suffer.

Common Signs:

• Wilting at midday, even when the soil is moist

• Blossoms dropping from tomatoes, peppers, beans, and squash

• Curling or rolling leaves (especially on tomatoes and corn)

• Sunscald on fruit and foliage
• Bolting in cool-season crops like lettuce, spinach, cilantro, and broccoli

When days top 94–96°F and nights stay above 70–75°F, tomato blossoms may drop and pollination can fail. Beans and peppers are even more heat-sensitive—blossoms can drop when temps reach the low 90s.

Tips to Beat the Heat:

• Water early and deeply so roots get moisture before the heat peaks

• Mulch with straw, shredded leaves, or compost to keep soil cool

• Use shade cloth or temporary shade for vulnerable crops
  

• Hold off on fertilizing during heatwaves—new growth is too fragile

• Group plants with similar water needs for better care

Always check soil moisture a few inches down. A damp surface can be deceiving.

Container and Raised Bed Gardening: Needs Extra TLC

Containers and raised beds are efficient and popular in Idaho gardens—but they dry out fast and heat up quickly in the sun.

Containers:

• Use light-colored or large pots to help keep roots cool

• Check moisture daily (or twice daily during extreme heat)

• Add mulch to container surfaces to reduce water loss

• Move pots to afternoon shade if you can, or use umbrellas or shade cloth

• Skip the fertilizer until the weather cools a bit

Raised Beds:

• Amend with compost to hold more water

• Water deeply and consistently—daily in temps over 90°F

• Use drip irrigation or soaker hoses to water efficiently

• Add 2–3 inches of mulch to moderate soil temperature swings

• Shade cool-season crops like lettuce and spinach to delay bolting

Raised beds and containers can be powerhouses—but only if you stay ahead of the heat.

Lawns: Tough, But Not Invincible

Cool-season grasses like Kentucky bluegrass, ryegrass, and tall fescue thrive in spring and fall. But when summer highs hang out above the mid-80s, even tough turf shows stress.

Heat-Stressed Lawn Signs:

• Grass looks dull green or bluish

• Footprints linger long after walking

• Growth slows, blades feel dry or brittle

Keep Lawns Alive Through Heat:

• Mow high—3–4 inches helps shade the soil

• Use a mulching mower to keep moisture and nutrients in the lawn

• Water deeply, aiming for 1–1.5 inches per week in 2–3 sessions

• Sharpen mower blades to reduce tearing

• Avoid fertilizing in peak heat

A lawn under stress doesn’t need rescuing—just steady, gentle care. With consistent watering and mowing, it’ll bounce back strong once cooler weather arrives.

Flower Beds: Fragile but Recoverable

Annuals and tender perennials often struggle most in summer heat. Blooms fade fast, leaves scorch, and plants may wilt even after watering.

Watch For:

• Drooping leaves

• Smaller or faded flowers

• Brown leaf tips

• Early flower drop

Flower Bed Survival Tips:

• Mulch to keep roots cool and moist

• Water at the base of plants to reduce disease and improve efficiency

• Choose heat-tough favorites like zinnias, lantana, marigolds, and black-eyed Susans

• Shade delicate flowers using nearby plants or lightweight covers

• Deadhead often to keep blooms coming without over-stressing the plant

Container-grown flowers may need water once or twice a day during heatwaves—and they’ll appreciate a break from that blazing afternoon sun.

Resilience Through the Heat

You can’t change the weather, but you can outsmart it. With a few adjustments—like early watering, smart mulching, temporary shade, and timing your tasks—you can help your garden survive and thrive through the hottest stretch of the year. Plants are surprisingly resilient. With a little help, they’ll bounce back beautifully once the heat breaks.

Additional Reading:

https://extension.oregonstate.edu/news/how-protect-yourself-your-plants-during-extreme-heat

https://extension.oregonstate.edu/gardening/flowers-shrubs-trees/heat-wave-garden-how-identify-prevent-heat-stress-plants

https://extension.sdstate.edu/heat-causes-problems-garden-produce

https://extension.usu.edu/archive/how-to-recognize-plant-heat-stress

Protect your plants from Powdery Mildew

Figure 1: PM on Tomato

 Powdery mildew is a fungal disease that affects a wide variety of plants. The affected plants have a dusted-with-flour appearance with white to gray powdery spots on the surface of leaves and fruits (Fig 1). It causes cosmetic damage, and defoliation and decreases the quantity and quality of fruit (Fig. 2).

Disease and Development 
There are many different species of (Powdery Mildew) fungi. Most species only attack specific plants in the same or closely related plant families.

Figure 3: PM on roses

For example, powdery mildew on roses does not spread to grapes.

Powdery Mildew fungi overwinter in buds, twigs, bark, and plant debris. Their spores are carried by wind to new hosts. Low relative humidity during the day favors spore dispersal.

Fig 2: PM on grapes

The optimum conditions for spores to germinate are temperatures between 68 to 77°F and high relative humidity (> 70%). Powdery Mildew spores can germinate in the absence of water and can infect in arid conditions (40% humidity). Water on plant surfaces can kill or inhibit germination. Spores and fungal growth are sensitive to extreme heat (above 90°F) and direct sunlight. Shady conditions are favorable for PM development.

Management
The disease triangle is a useful tool to understand and manage diseases like Powdery Mildew (Fig. 3). The severity of Powdery Mildew infections is a function of the presence of the pathogen, the host susceptibility, and the environment. Powdery Mildew can be managed by good cultural practices.   

Fig 3: The Disease Triangle

The best control is to plant only resistant species or cultivars. Avoid excess fertilizer since plants with abundant succulent tissues are more susceptible to infection. The fungi can be eliminated by removing and burning all infected plant tissues and debris. Tools must be disinfected after use.

Another good control method is making environmental conditions less favorable for the disease. Avoid dense canopies by proper plant spacing and pruning to provide good air circulation, reduce humidity and increase sunlight penetration. Plants should not be planted in poorly drained soils or shady damp areas.

Overhead watering of the leaves during the day and when humidity is low can reduce infection. Water washes spores off the plant and inhibits its germination. This control method is not recommended for vegetables since it may contribute to other pest problems.

Powdery Mildew seldom needs chemical control in residential plantings, but it may be warranted in commercial plantings of susceptible crops like grapes and cucurbits. Chemicals are most effective when combined with cultural control. They should be applied before the disease symptoms appear. Further spread may be stopped or slowed with chemical treatment. Materials like horticultural oil or neem oils have a low environmental impact. Apply every 7 to 14 days throughout the season. Do not apply to drought-stress plants when the air temperature is above 85° nor within 2 weeks of a sulfur spray. Wettable sulfur is very effective in preventing infection. Like oil application, it should not be applied when the air temperature is over 90° nor within 2 weeks of an oil application.

Feeding the Summer Garden: A Practical Guide to Fertilizing

By July, gardens in the Boise area are alive with activity. Tomato vines climb their cages, squash leaves stretch across beds, and pollinators hum from blossom to blossom. But while the season’s early work is behind us, another critical task emerges: feeding the garden.

Plants are living systems, constantly drawing nutrients from the soil to fuel growth, flowering, and fruiting. As those nutrients are used up, the soil alone often can’t keep up with the demand—especially in raised beds, containers, or sandy soils common in southern Idaho. Understanding how to fertilize makes all the difference.

This guide walks through the most common fertilizing methods home gardeners use, when and why they matter, and how to apply them effectively.

Side-Dressing: A Midsummer Nutrient Boost

Side-dressing is the practice of applying fertilizer in a narrow band a few inches away from the base of a plant and watering it in. It's especially useful in July for long-season, heavy-feeding crops like tomatoes, peppers, squash, and corn.

In early summer, nitrogen-rich materials (like urea, blood meal, or calcium nitrate) can support foliage development. But by midseason, as plants begin flowering and fruiting, excessive nitrogen can cause more leaf growth at the expense of blooms and harvest.

In July, a better choice is a balanced fertilizer (e.g., 5-10-10) or one higher in phosphorus and potassium to support flowering and fruit development. Organic options include composted manure, bone meal (typically 3-15-0), or natural blends formulated for tomatoes or vegetables.

Fertilizer should be applied 4–6 inches from the stem and gently worked into the soil or covered with mulch. Always water thoroughly after applying.

Top-Dressing: Slow and Gentle

Top-dressing is the process of applying compost or granular fertilizer to the soil surface around plants. It requires no digging and is ideal for leafy greens, herbs, root crops, and perennials—or anywhere you want to avoid disturbing roots.

This method supports soil structure, boosts moisture retention, and releases nutrients slowly. It’s especially well suited for use with compost or slow-release organic fertilizers. Mulching after top-dressing can further improve moisture retention and soil health.

Top-dressing can be repeated every few weeks throughout the growing season, especially after heavy rains or heat waves.

Liquid Feeding: Fast and Effective

Liquid fertilizers are mixed with water and poured around the base of the plant. This method is particularly effective in July when container-grown plants and raised beds may need quicker nutrient access due to faster drying and leaching.

Liquid soil drenches can be made from fish emulsion, compost tea, kelp extract, or water-soluble commercial fertilizers. Apply every 1–2 weeks as needed.

This method is fast-acting and easy to tailor, especially for vegetables like cucumbers, squash, or tomatoes that show nutrient stress mid-season.

Foliar Feeding: Targeted and Temporary

Foliar feeding involves spraying a diluted fertilizer solution directly onto plant leaves. It’s sometimes used to address visible nutrient deficiencies or to support plants under short-term stress.

While plants can absorb some nutrients through their leaves—especially micronutrients like iron, magnesium, or calcium—this method is usually most effective as a supplement, not a replacement for soil fertilization. Effectiveness depends on nutrient type, leaf age, and weather conditions.

Foliar sprays may help:

• Correct specific deficiencies quickly
• Support stressed or struggling plants
• Bypass root-zone issues temporarily

However, they can also:

• Burn leaves if applied in hot, dry weather
• Offer only short-term results
• Increase disease or runoff risk if overused

Apply foliar sprays only when clearly needed, and always during cooler parts of the day—morning or evening. For most gardens, foliar feeding plays a limited, supportive role, best reserved for micronutrient issues or recovery from stress.

Pre-Plant Incorporation: Building the Foundation

Though not a July task, it’s worth noting that much of a garden’s nutrient supply should be in place before planting. Mixing compost and a balanced fertilizer into beds in early spring provides a steady source of nutrients as plants establish.

This early step is especially important for root development and early vegetative growth. Soil testing can help fine-tune what’s needed.

Summary Table

Method	Best Use	Midseason (July) Application
Side-Dressing	Fruiting vegetables	Use balanced or low-nitrogen blends
Top-Dressing	Leafy greens, herbs, perennials	Apply compost or slow-release fertilizer
Liquid Feeding	Containers, raised beds	Every 1–2 weeks with water
Foliar Feeding	Nutrient deficiencies, stress	Use selectively; best for micronutrients
Pre-Plant Mix	All crops	Done at planting; provides base nutrition

Final Thoughts

Fertilizing in July is about balance. The garden is in full gear, and plants need support—but not too much. Focus on what your soil and plants are telling you. Look for signs of deficiency, evaluate past applications, and use the right method for the right crop at the right time.

Fertilizing smart in midsummer can mean the difference between a sluggish garden and a bountiful harvest.

For Additional Reading:

Mid-Season Boost for Hungry Plants

Foliar Feeding

Fertilizing your garden:Vegetables, Fruits, and Ornamentals