Moss on the roof; keeping guacamole green — The Boston Globe

Moss on the roof; keeping guacamole green - The Boston Globe

August 9, 2007

Make sure the growth is moss, not algae. Look down from an upstairs window, inspect it from a ladder, or ask a roofing company to examine it for you: If the green material looks like a thin film of paint, it’s probably algae, says James R. Kirby, senior technical director for the National Roofing Contractors’ Association.

Moss is thicker, with stem and leaflike protrusions, and tends to build up in the crevices between shingles. While algae is harmless, many experts believe that moss damages a roof by trapping moisture, which deteriorates wooden and asphalt shingles. The plants’ rootlike structures may also penetrate roofing materials, breaking them apart over time.

A roof-cleaning company can remove moss (or algae) with a power washer. But this process may dislodge surface granules on asphalt, making the roof susceptible to damage from ultraviolet light; it also may wear down wooden shingles. Applying a moss-eradication product is another option. Choose one that contains soap salts, as these break down rapidly in soil. Administer the products with a garden sprayer, or hire a roof-cleaning company to do it.

Since moss thrives in moist, shady conditions, you can take steps to prevent future growth by clearing your roof of leaves and trimming back any overhanging tree branches. If the problem returns, a roofer can install zinc or copper strips near the top of the roof. Rainwater floods over them, covering the roof with small amounts of the metals, which prevent new moss from growing. Because zinc and copper often find their way into rivers and streams, where they can be toxic to fish, avoid this treatment if you live near a body of water.

Finally, when it’s time to reroof, consider switching to metal. This surface, which is coated to prevent harmful runoff, is too slick for moss to grow on.

My guacamole turns brown in the refrigerator. How can I prevent this?

Fruits and vegetables such as avocados, bananas, apples, peaches, pears, and potatoes contain enzymes that cause their flesh to turn brown when exposed to air. The discolored flesh is not harmful or even perceptible by taste, but it doesn’t look very appetizing.

The easiest way to keep guacamole from browning is to prepare it just before serving. Add a little lemon or lime juice if the recipe doesn’t already call for it: Acids slow the browning process. If you want to make guacamole ahead, squeeze extra citrus juice over the surface. This barrier reduces the amount of oxygen to which the dip is exposed. Press plastic wrap onto the surface of the guacamole and refrigerate for up to two days.

Some browning will still occur if guacamole is left for several hours or more. Scrape off the top layer before serving to reveal the vibrant green dip below.

Adapted from Martha Stewart Living Magazine. Questions should be addressed to Ask Martha, care of Letters Department, Martha Stewart Living, 11 W. 42d Street, New York, N.Y. 10036. Questions may also be sent by e-mail to: Please include your name, address, and daytime telephone number. Questions of general interest will be answered in this column; Martha Stewart regrets that unpublished letters cannot be answered individually. For more information on the topics covered in the Ask Martha column, visit .

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