You can custom blend your own greenhouse whitewash to control light penetration in the summer months. Greenhouse whitewash is traditionally made by hydrating lime for a white paint. Modern versions often call for a simple dilution of latex paint. Whitewash is generally applied to the outside of the greenhouse. Precipitation tends to gradually wear away at the sunblock over the course of the summer months. Protect growing greenhouse plants with an inexpensive homemade whitewash blend.
Pour the quicklime or white latex paint into the bottom of a 10-gallon bucket.
Attach a paint mixer bit to the end of an electric drill. Lower the mixer bit into the bucket until it touches the bottom.
Add 2 gallons of water to the bucket. Stir the mixture at low speed with the electric drill. Slowly pour in 2 more gallons of water as you continue mixing.
Dip a paintbrush in the whitewash when it appears evenly blended. Paint a small inconspicuous area on the outside of the greenhouse glass with a thin layer of your whitewash. View the painted area from inside the greenhouse after 20 minutes have passed.
Dilute the whitewash with another 2 to 4 qts. of water if the current shade is too opaque. Mix the blend thoroughly with the drill before testing a new area. Seal the bucket of customized greenhouse whitewash until you are ready to use it.