Fertilizing Trees and Shrubs in the Heat: Dos and Don’ts

As summer temperatures soar, even the most established trees and shrubs can show signs of stress: wilting leaves, slowed growth, yellowing, or early leaf drop. While it may seem counterintuitive to fertilize during such extreme conditions, proper mid-season nutrition can help your plants recover, sustain health, and prepare for the cooler months ahead. The key is choosing the right fertilizer and applying it the right way.

This guide covers the safest and most effective ways to fertilize trees and shrubs during hot weather, using insights from soil science, professional landscapers, and proven products like those offered by Supply Solutions LLC.

Why Summer Fertilization Matters for Woody Plants

Unlike annuals and vegetables, trees and shrubs are long-term landscape investments. Summer fertilization helps them:

• Replenish nutrients lost to spring growth spurts
• Strengthen root systems for drought resistance
• Support leaf recovery after pest or disease pressure
• Prepare for late-summer flowering and seed production

However, summer is also a high-risk period for fertilizer burn, nutrient runoff, and overgrowth. A strategic, minimalistic approach is best.

When to Fertilize (And When Not To)

Best time:

• Early morning or late evening, during mild weather
• After rainfall or deep watering, when soil is moist

Avoid fertilizing:

• During drought without irrigation
• If foliage is scorched or plants are wilted
• Right before a heatwave or heavy storm

Timing is especially important with fast-acting fertilizers like ammonium sulfate or liquid NPK blends.

Best Fertilizers for Summer Trees and Shrubs

1. 12-6-6 Ornamental Blend

• Designed for woody ornamentals and perennials
• Provides nitrogen for recovery, phosphorus for root support, and potassium for stress resistance

2. 10-10-10 with Micronutrients

• Great for broad-spectrum feeding on nutrient-depleted soils
• Delivers balanced growth without overstimulating foliage

3. 15.5-0-0 Calcium Nitrate

• Ideal for trees showing signs of calcium deficiency (leaf tip burn, weak growth)
• Improves drought resistance and new wood strength

Application Tips for Safety and Effectiveness

• Water deeply before and after applying to avoid root burn
• Apply fertilizer under the drip line (edge of the canopy), where feeder roots are most active
• For newly planted trees and shrubs, apply at half-strength to avoid stress
• Use liquid or water-soluble products during summer for gentler, more targeted feeding

Common Mistakes to Avoid

Over-fertilizing: Mid-season is not the time to force growth. Too much nitrogen can overstimulate soft tissue, making plants vulnerable to heat stress and insects.

Dry soil feeding: Always water beforehand to improve uptake and protect roots.

Wrong product choice: Avoid using high-nitrogen lawn fertilizers around trees. Choose blends specifically formulated for woody plants.

Ignoring pH: Some tree and shrub species are sensitive to soil pH. For example, azaleas and rhododendrons prefer acidic conditions.

Tailoring Your Fertilizer Choice to Plant Type

Plant Type	Best Fertilizer Option
Flowering shrubs	10-10-10 w/ micronutrients + calcium nitrate
Deciduous trees	12-6-6 or 15.5-0-0, depending on soil test
Evergreens	12-6-6 or ammonium sulfate for green-up
Acid-loving plants	Ammonium sulfate (lowers soil pH slightly)

Soil Testing: A Mid-Summer Advantage

If your trees and shrubs aren’t thriving, don’t guess—test. A soil test can reveal:

• Nutrient imbalances
• Organic matter levels
• Soil pH issues

This allows you to apply exactly what’s needed and nothing more, improving plant health while reducing waste.

Sustainable Practices for Summer Fertilization

• Use mulch to conserve moisture and reduce nutrient leaching
• Pair fertilization with compost tea to encourage microbial activity
• Avoid fertilizing near water bodies or on compacted soil
• Choose products from trusted suppliers like Supply Solutions LLC, who specialize in formulations for landscape and agriculture use

Final Thoughts

Fertilizing trees and shrubs in the summer doesn’t have to be risky if done thoughtfully. By choosing appropriate fertilizers like 12-6-6, 10-10-10, or calcium nitrate, and timing your application carefully, you can help your woody plants recover from early-season stress and maintain their health through the heat.

Have questions or want help selecting the right product?

• Call us at 503-451-1622
• Email sales@mysolutionssupply.com
• Use our Contact Form
• Message us on Facebook

Let Supply Solutions LLC help you protect your landscape investment all summer long.