June 06, 2026

Heat, Pests, Mold and More: Wood Mulch in the Summer Months

Wood Mulch is Popular but There are Issues to Consider

Wood mulch is one of the most popular ground cover choices in the country, and for good reason. It's affordable, widely available, and looks natural in almost any landscape. But as temperatures climb each summer, a set of well-known problems begin to compound. If you manage a playground, maintain a garden bed, or oversee a commercial landscape, here's what to watch for once the heat sets in.

1. It Gets Dangerously Hot

Wood mulch absorbs and retains heat. In direct summer sun, the surface temperature of dark wood mulch can climb significantly above air temperature, making it uncomfortable or even dangerous for children playing barefoot or crawling on playground surfaces. This is particularly concerning in the hours between late morning and mid-afternoon when sun exposure peaks.

Unlike hard surfaces such as asphalt or concrete, hot wood mulch isn't always visually obvious. It can look perfectly normal while radiating enough heat to cause discomfort or burns on sensitive skin. For playground operators, this is a liability issue that rarely makes it onto the inspection checklist.

2. It Compacts and Loses Impact Protection

Summer heat dries wood mulch out rapidly. As moisture evaporates, chips shrink, shift, and begin forming a compacted mat (sometimes called a "mulch crust") on the surface. This crust repels water, reduces drainage, and most importantly for playgrounds, significantly reduces impact attenuation.

A playground surface that met ASTM F1292 impact attenuation standards at installation may fall below safe levels by midsummer simply due to heat-driven compaction and depth loss. This is the same failure condition seen with frozen wood mulch in winter, just caused by the opposite extreme of temperature.

3. Mold and Fungus Move In

Warm temperatures combined with summer rain create ideal conditions for fungal growth in wood mulch. The most notorious offender is artillery fungus (Sphaerobolus stellatus), a wood-loving organism that thrives in moist mulch beds and launches sticky black spores onto nearby surfaces, including siding, cars, and outdoor furniture. Those spores are notoriously difficult to remove once they adhere.

Beyond artillery fungus, general mold growth in wood mulch is common during humid summer months, presenting aesthetic problems in garden beds and potential health concerns in areas where children play. For a deeper look at how rubber mulch addresses this issue, see our post on effective mold and fungi prevention with rubber mulch.

4. Pests Use It as a Home Base

Summer is peak season for termites, carpenter ants, earwigs, and a variety of other insects, and wood mulch is one of their preferred habitats. Moist, decomposing wood close to a home's foundation is an open invitation for termite activity in particular. Many pest control professionals recommend keeping wood mulch at least six inches away from foundations for exactly this reason.

In playground settings, insect activity in wood mulch is not just an annoyance. It's a safety concern for children who spend extended time in contact with the surface. Rubber mulch, being inorganic, provides no food source or habitat for wood-boring or moisture-seeking insects. Learn more about why rubber mulch works well against pests.

5. It Breaks Down Fast and Needs Constant Replenishment

Heat accelerates decomposition. What took a full year to break down in moderate climates can degrade in a single summer in hot, humid regions. As wood mulch decomposes, it loses volume, meaning the depth of your surface drops steadily throughout the season. For garden beds, this means more frequent top-offs. For playgrounds, it means a surface that may look adequate but no longer provides the fall protection depth it was designed to deliver.

This ongoing replenishment cost adds up quickly. A homeowner might apply fresh wood mulch every spring only to find it significantly depleted by August. A parks department managing multiple playgrounds faces this expense multiplied across every site.

The Summer-Proof Alternative

Rubber mulch addresses every one of these issues at the source:

Heat — rubber mulch stays cooler than dark rock and significantly cooler than asphalt; its surface temperature is far more manageable than compacted dark wood mulch in direct sun
Compaction — rubber mulch doesn't dry out, shrink, or form a crust; it maintains its depth and impact performance through summer without intervention
Mold and fungus — as an inorganic material, rubber mulch provides no organic matter for fungi to feed on
Pests — no food source, no moisture retention, no habitat for wood-boring insects
Decomposition — rubber mulch doesn't break down, which means no mid-season replenishment and no ongoing material cost

For a full side-by-side comparison, see Rubber Mulch vs. Wood Mulch: Here's How to Decide.

Frequently Asked Questions

Does wood mulch attract termites?
Wood mulch can attract termites, particularly when it's kept moist and placed close to a home's foundation. Pest control professionals typically recommend maintaining a mulch-free buffer zone around foundations and choosing inorganic alternatives in high-risk areas.

Why does wood mulch get moldy in summer?
Mold and fungus thrive in warm, moist organic material. Summer heat combined with rain or irrigation creates ideal conditions for fungal growth in wood mulch beds. Artillery fungus is a particularly problematic species that can stain nearby surfaces with sticky black spores.

Does wood mulch lose its impact protection in summer?
Yes. Heat-driven compaction and depth loss can reduce wood mulch below safe fall protection levels over the course of a summer, even if it was properly installed in spring. Playground surfaces should be checked regularly for adequate depth throughout the season.

How often does wood mulch need to be replaced in summer?
In hot climates, wood mulch may need replenishment as frequently as mid-season, particularly in sunny, high-traffic areas. Decomposition and compaction reduce depth faster in summer than in cooler months.

Ready to upgrade to a ground cover that performs all year long, no matter the season? Explore our rubber mulch options and see why homeowners, schools, and landscape professionals across the country are making the switch.