Published: July 7, 2025 · Last updated: July 7, 2025

Why Your Concrete Turns Green in Summer

Every summer, homeowners across Point Pleasant and the Jersey Shore notice the same frustrating thing: their concrete is turning green. Driveways, sidewalks, patios, and pool decks that looked perfectly fine in the spring start developing a green film that gets worse as the summer goes on. If this sounds familiar, you are not alone, and the cause is simpler than you might think.

That green discoloration is algae, and it loves the warm, humid conditions that define a New Jersey summer. Understanding why it grows and what actually works to remove it can save you time, money, and a lot of frustration.

The Culprit: Algae on Your Concrete

The green coating on your concrete is a type of algae, sometimes accompanied by moss or lichen in heavily shaded areas. Algae spores are everywhere, carried by wind, rain, and even foot traffic. They are microscopic and impossible to avoid. What determines whether algae takes hold on your concrete is not whether the spores are present but whether conditions are right for them to grow.

Concrete is a naturally porous material, which means it absorbs and retains moisture. That porosity gives algae spores a textured surface to cling to and a moisture source to feed on. Once algae finds a foothold, it can spread across a concrete surface surprisingly fast, especially in the right conditions.

Why Summer Is the Worst Season for Green Growth

Algae needs three things to thrive: moisture, warmth, and some degree of shade or limited direct sunlight. Summer in New Jersey delivers all three in abundance. The combination of high humidity, frequent afternoon thunderstorms, and temperatures in the eighties and nineties creates an ideal environment for rapid algae growth.

Here along the Jersey Shore, the proximity to the ocean adds another layer. Coastal humidity stays elevated even on days when areas farther inland dry out. Morning dew is heavier and lasts longer. Your concrete barely gets a chance to fully dry before the next cycle of moisture begins. It is no wonder that green growth seems to appear almost overnight during July and August.

Shaded Areas Are Ground Zero

Take a look at where the green growth is worst on your property. Chances are it is concentrated in shaded areas: the north side of your house, under trees, behind shrubs, or anywhere that does not get consistent direct sunlight. That is because sunlight is a natural algae killer. UV rays dry out surfaces and inhibit algae growth.

In Point Pleasant, many homes have mature trees that provide wonderful shade in the summer but also create the damp, shaded conditions that algae loves. If your driveway or patio is partially covered by tree canopy, you will almost certainly deal with more green growth than a neighbor whose property sits in full sun. This is not something you can easily change about your property, which makes regular cleaning all the more important.

Sprinkler Overspray and Poor Drainage

Another common contributor to green concrete is sprinkler overspray. If your irrigation system is hitting your driveway, sidewalk, or patio, you are essentially watering your algae every time the sprinklers run. Even a small amount of overspray that reaches concrete can keep it damp enough to support aggressive algae growth.

Poor drainage is equally problematic. If water pools on your concrete after rain or if your property slopes in a way that directs runoff across your driveway, those areas will stay wetter longer and develop green growth faster. Adjusting sprinkler heads to avoid hitting hardscaped surfaces and addressing any drainage issues are simple steps that can make a real difference.

Why Bleach Is Only a Temporary Fix

When homeowners spot green algae on their concrete, the first instinct is often to grab a jug of household bleach. And to be fair, bleach does kill surface algae on contact. You will see the green disappear almost immediately, which feels satisfying. But here is the problem: bleach only works on the surface layer. It does not penetrate deeply enough into the porous concrete to kill the algae at its root.

Within two to four weeks, the algae grows right back. You end up in an endless cycle of bleaching and re-bleaching that wastes your time and money while potentially damaging your concrete and harming nearby plants. Bleach can also discolor concrete over time and is harmful to your landscaping if it runs off into garden beds or your lawn.

The Risks of DIY Algae Removal

Beyond bleach, some homeowners try renting a pressure washer and tackling the job themselves. While this can remove surface algae, consumer-grade pressure washers often lack the power to fully clean embedded growth. Worse, without the right technique, you can etch lines into your concrete, damage the surface, or create an uneven appearance that looks worse than the algae did.

There is also the issue of cleaning solutions. The products available at hardware stores are a step above bleach but still pale in comparison to the commercial-grade solutions that professionals use. Effective algae removal requires the right combination of pressure, technique, and cleaning chemistry, and getting any of those wrong leads to disappointing results.

Professional Cleaning for Lasting Results

The most effective way to deal with green concrete is professional pressure washing that combines high-powered equipment with commercial-grade cleaning agents. At Point Pleasant Pro Wash, our concrete cleaning service does not just blast algae off the surface. We apply treatments that penetrate into the pores of the concrete and kill algae at the root, which means it takes significantly longer for the growth to return.

We also use surface cleaning attachments that deliver uniform results across the entire area, avoiding the streaky, inconsistent look that handheld wands often produce. The difference between a DIY job and a professional cleaning is immediately visible, and the results last months longer.

For homeowners in Point Pleasant and across the Jersey Shore, we recommend scheduling a concrete cleaning in early summer before algae growth peaks, and a follow-up in early fall to clear anything that developed during the hottest months. This keeps your concrete safe, clean, and looking great year-round.