Work phosphorus thoroughly into soil to prevent runoff pollution

A soil test recommended adding a lot of phosphorus to my new shrub bed this spring. The soil was very low in phosphorus, and I worked it in well before planting. Should I add more this fall?

It's good that you thoroughly worked the phosphorus into the soil, because phosphorus is one of the big polluters of the Chesapeake Bay. It's important to prevent it from being washed into storm drains or waterways that lead to the bay. Phosphorus binds with soil and is not volatile like nitrogen, so the full application you already made should suffice for years to come. Repeat the soil test in three to four years.

I have dahlias growing in a pot outside. Instead of removing the rhizomes this fall, storing and replanting them in the spring, can't I just store the potted plants indoors over the winter?

It may be possible, but consider that insects may come indoors in the soil. Also, the rhizomes need to overwinter dry so they don't rot, yet not so dry that they shrivel and lose moisture. Dahlias are fairly heavy "feeders" and will need good organic soil next year, plus a balanced fertilizer to replace nutrients used up in the potting soil this summer.

University of Maryland Extension's Home and Garden Information Center offers free gardening and pest information. Call 800-342-2507 or send a question to its website at extension.umd.edu/hgic.

Plant of the week

Papaw

Asimina triloba

Wouldn't you know that America's largest native fruit would be exceptional? The green or yellow papaw fruit, ripening in September-October, has the startling flavor of bananas, plus undertones of vanilla, pineapple and mango. The 1- to 21/2-inch mauve-purple flowers start female and then go male. Germinating seedlings are killed by direct sunlight, yet later enjoy sun. Papaw trees grow to about 25 feet, with large leaves that turn into clear yellow foliage in fall. In the wild, these understory trees form thickets, but lawn mowers stop that in home landscapes. Plant in slightly acidic, well-drained soil. Because they are not self-fertile, purchase two plants — either two seed-grown or two different grafted varieties. Named varieties produce the best-quality fruit.

—Ellen Nibali

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