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Q&A: Scale, Grass Clippings and Cedars

Master gardener Paul James explains how to make an all-natural fungicide, spray terra-cotta pots, avoid soil compaction and control scale.

Master gardener Paul James answers viewer questions.

Q: You often recommend baking soda as a fungicide, but won't it raise the pH of the soil?

A: I often recommend a formulation containing baking soda as an all-natural fungicide. To make the concoction, mix one tablespoon each baking soda, horticultural oil and insecticidal soap in one gallon of water. Shake well and spray affected plants every seven to 10 days.

Because it's alkaline, baking soda certainly does have the potential to raise the pH of the soil, but only if you use a lot of it. Frankly, the only time in which it might pose a problem is if you spray it on plants that require acidic soils, such as azaleas, rhododendrons and blueberries.

In that case, you might want to periodically – about once or twice a year – apply sulfur to the base of those plants, work it lightly into the soil, and water well. Sulfur is acidic, meaning it will lower the pH, and therefore counter the effect of the baking soda.

Q. Why are plants that aren't actually cedars called cedars?

A: I don't really know, but maybe it's because people might be more willing to buy something with a familiar name rather than one with a more complicated name. For example, one such conifer sold in the trade is labeled "Alaskan cedar," when in fact it's a Chamaecyparis or false cypress. Red cedar is actually a juniper.

Truth is, there are only four species of cedar: Cedrus atlantica, the most familiar of which are the upright and weeping blue forms; Cedrus brevifolia, which is hard to find; Cedrus deodara, also known as the Deodar cedar; and Cedrus libani, the cedar of Lebanon. Within each species there are several cultivars, but there are still only four species of cedar.

Q. To avoid soil compaction, I stand on a board while working in the garden. But the board attracts slugs galore. Is there a better way?

A. You're smart to use the board because it distributes your weight over the soil such that compaction is minimal. However, the board serves as a sort of slug trap because slugs love damp, dark places. This plastic path unrolls in a garden bed so you can walk on it to minimize soil compaction. When you're done, roll it back up again and move on to the next bed.

It also comes in handy when you need to work on wet or muddy soil, and you can hose it off when you're done. The only downside is that you have to assemble the path yourself, a process that takes about 30 minutes to complete.

Q. My friend says that goldenrod is just another name for ragweed and that it causes the same allergic reaction. I disagree. Who is right?

A. Goldenrod (Solidago) is a late-summer flowering perennial that's readily available in nurseries and is often used in floral arrangements as well. It's similar in appearance to ragweed, but far fewer people are allergic to its pollen. Ragweed is in a different genus (Ambrosia).

Q. Can you tell me about a plant called Selaginella?

A. Selaginella is available in several species. These plants look like part moss, part fern, but in fact they're neither. Actually, selaginellas are lycopods, an ancient family of plants. Some species are hardy to USDA Zone 6, and they make great container plants or groundcovers. They need moist, well-draining soil and shade and are relatively care-free.

Q. Can I use glass clippings as mulch?

A. Yes, but use them sparingly. If applied too thickly, they can mat down and become compacted to the point where water can't easily penetrate. A one-inch layer is ideal. Keep in mind that if you use synthetic fertilizers and herbicides on your lawn, those chemicals will remain in your grass clippings, so you don't want to use contaminated grass clippings to mulch the vegetable garden.

Q. What is scale, and how do you control it?

A. Scale is a type of insect that can cause major damage to plants. There are several different species of scale, all of which can be very destructive because they multiply rapidly, often producing several generations a year, and because they have long, flexible beaks that they use to suck the sap from plants. Armored scale has a hard shell, and once they settle on a plant, they don't move. They just sit there and suck the life out of plants. There is also soft-bodied scale. However, all scale insects can be controlled using horticultural oil or neem oil, both of which smother these nasty critters.

Q. Can I overwinter my pencil tree as a houseplant?

A. Yes, the pencil tree is hardy only to USDA Zone 10, so you should move it indoors when temperatures hover around 50 degrees F. Place it a sunny location and only water it sporadically.

As is the case with many other euphorbias, the sap of the pencil plant is poisonous and may cause contact dermatitis. So if one of the pencil-like stems snaps off, handle it with care. Also, if you want more plants, just stick the "pencil" in a pot full of moist vermiculite or perlite, and it'll form new roots within a few weeks.

Q. Can you paint terra-cotta pots?

A. Yes, but you have to buy the right paint. Opt for a spray paint that is labeled for use on clay. It's readily available in several colors and easy to apply. On new pots, all you do is spray the paint on lightly and evenly, let it dry 15 minutes, apply a second coat, and let that dry about four hours. On old pots, scrub the surfaces with soap and water and let the pot dry before applying the paint. These paints are available with a textured surface or flat finish.

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