Winter is when synthetic grass tennis courts can start to get away from you.

A few wet weeks, humid conditions and shaded court areas can be enough for algae to begin forming. At first, it may only appear as small black spots in Northern shaded areas. Left untreated, those spots can become black patches, then larger damp areas that look poor, hold moisture and become slippery underfoot.

This is the classic “stitch in time saves nine” moment.

The good news is that if you act early, there is a simple DIY treatment approach that can help bring the surface back under control before the problem becomes harder work.

Why winter algae appears on synthetic grass courts

Winter creates ideal conditions for algae and moss growth:

• More moisture sitting in the surface
• Less direct sunlight, especially in shaded areas
• Cooler conditions that slow natural drying
• Organic matter and surface buildup holding dampness in the pile

The first places to check are shaded ends, generally in the North,  corners, fence lines, areas near overhanging trees and any part of the court that stays damp after rain.

What to look for

Walk the court and look for:

• Small black spots in shaded areas
• Black patches beginning to spread
• Areas that stay damp longer than the rest of the court
• Slippery or greasy sections underfoot
• Bright green moss sitting above the synthetic grass pile

The earlier you act, the simpler the job is.

If you are an early bird treating black spots and small patches

This approach is for early-stage algae where you are seeing black spots or smaller patches, but the growth has not become thick, raised or bright green.

What you need

Check the SportsClean website and have these ready before you start: 

• Salt – 10kg bag
• Synthetic Grass Treatment Concentrate – 2L / 5L
  For most algae treatment jobs, consider having 2–3 x 5L bottles available, depending on the affected area.
• Tennis Court Scraper
• Synthetic Grass Sand – 20kg bag for finishing and topping up repaired areas if required.

Step-by-step treatment

1. Spray the affected area

Follow the instructions on the Synthetic Grass Treatment Concentrate container and apply the treatment to the black spot or patch.

There is also a demonstration video on the Sports Clean webshop product page showing the treatment being applied

2. Apply salt lightly

Lightly spread salt over the now-sprayed black area.

Do not overdo it. The goal is a light, even application over the affected section.

3. Lightly broom for even coverage

Use a broom to lightly even out the salt across the treated area. The aim is to distribute it through the affected section without damaging the surface.

4. Leave it for 2–3 weeks

Give the treatment time to work.

The black areas may turn brown as the algae dies off. This is expected.

5. Scrape out the dead material

After 2–3 weeks, use a Tennis Court Scraper to remove the dead algae and surface buildup.

Remove all scrapings from the court. Do not leave the material sitting on the surface, it will infect.

6. Finish the repaired area

Add a small amount of Synthetic Grass Sand if the area needs topping up, then add a light sprinkling of salt and brush it in evenly.

If the algae or moss is more advanced

This approach is for areas where the black patches have become more aggressive, are sitting above the synthetic grass pile, or have turned into bright green moss.

There is still a DIY option, but it will take more effort.

What you need

Have these ready:

• Salt – 10kg bag — likely 2 bags depending on the affected area
• Synthetic Grass Treatment Concentrate – 2L / 5L
  Consider 2–3 x 5L bottles depending on court condition and treatment area.
• Tennis Court Scraper
• Stiff Bristle Broom
• Synthetic Grass Sand – 20kg bag for finishing if required.

Step-by-step treatment

1. Scrape out the infected areas first

Use the Tennis Court Scraper to remove the infected surface material.

Take care to remove all scrapings from the court. This is important. If the material is left behind, it can continue to hold moisture and contaminate the surface.

2. Spray the affected area

Follow the instructions on the Synthetic Grass Treatment Concentrate container and apply the treatment to the black spot or patch.

There is also a demonstration video on the Sports Clean webshop product page showing the treatment being applied

3. Apply salt lightly

Lightly spread salt over the scraped infected area.

4. Broom the affected section

Use the Stiff Bristle Broom to evenly work the salt across the infected area.

Focus on the affected section only.

A demonstration video is available on the Sports Clean webshop product page.

5. Leave it for 2–3 weeks

Allow the treatment to work over the next 2–3 weeks.

The black areas may turn brown as the growth dies off.

6. Scrape again and remove all material SCRAPINGS

After 2–3 weeks, scrape out the remaining dead algae or moss.

Again, remove all scrapings from the court.

7. Repair and finish the area

Add a small amount of Synthetic Grass Sand where needed, apply a light sprinkling of salt, and brush the area evenly.

A simple winter court check routine

During winter, make it a habit to inspect the court after wet weather.

Pay particular attention to:

• Shaded ends
• Corners
• Fence lines
• Tree-covered areas
• Low-use sections of the court
• Areas where water or debris collects

A short inspection every couple of weeks can save a much bigger clean-up later.

Keep your court ready for play

A synthetic grass tennis court should be safe, clean and ready to use. Winter algae and moss can make the court look unattractive, hold moisture and become slippery, but early action makes a big difference.

If you see black spots, treat them early.

If the algae has already advanced, give the area a more thorough scrape, spray,and salt treatment process.

Either way, the right winter maintenance routine will help protect the surface and keep your court ready for play.

Products mentioned in this guide

• Synthetic Grass Treatment Concentrate – 2L / 5L
• Salt – 10kg bag
• Tennis Court Scraper
• Stiff Bristle Broom
• Synthetic Grass Sand – 20kg bag

Need help choosing the right products for your court?
Visit the Sports Clean webshop or contact the team for advice.