Gardening questions answered

By Kathy Hatfield
Gardening Columnist

Back to Gardening Articles List

There have been a lot of questions lately about dividing iris and other perennials. Generally I don't plant or transplant anything during the hottest part of the summer. Even with extra watering, some plants will not survive the stress of being transplanted. Here are a few frequently asked questions.

Q: When is the best time to divide and transplant my irises?

A: Because irises bloom in the spring, all their energy is going into the blooming process. After they have bloomed, the plant can then put its energy into growing roots and rhizomes. So it's best to wait until at least mid-summer, but preferably later, to transplant irises. If you divide and transplant irises in August or September, there will be time to develop good root systems. Also, dividing them later in the summer or in early fall will give them a chance to set their blossoms for next year.

Q: Do reblooming irises really bloom more than once and do they need any special treatment that is different from standard irises?

A: Reblooming irises will usually bloom once in the spring and again in the summer. Sometimes, they will bloom as many as four times in one season.

Rebloomers need at least 5 hours of sun each day, and because they produce more flowers, it's a good idea to fertilize them spring and summer. Use a balanced fertilizer; if they have too much nitrogen they'll produce lots of foliage and few flowers.

Besides improving the overall appearance of the plant, the spent flower stalks of reblooming irises should be cut back to encourage new flowers. By cutting the stalks after they flower, the plant will not spend its energy producing seeds, but instead will produce new flowers.

Q: Why do some of my tomatoes turn brown or black and look rotten on the bottom?

A: Your tomatoes are suffering from blossom end rot, which means they are deficient in calcium. With acid soils, you might want to add lime, since it is a good source of calcium. But most of us have alkaline soils, and adding lime will only make soil more alkaline. Irregular watering could also cause the calcium to be unavailable to the plant. Try to maintain a regular watering schedule. Using a soaker hose and mulch helps to keep soil moisture consistent. There are also products at garden centers that can be added to the soil when transplanting or sprayed on the plants when they set fruit. Follow label directions carefully.

Q: Is it safe to use coffee grounds in my garden?

A: Coffee grounds make a great addition to your garden or compost pile. Because they are so small, the granules break down quickly, adding humus to the soil and improving its texture. Also, acidic coffee grounds are a welcome addition to our alkaline soils. Add them to compost or mix them into the soil so that they are not highly concentrated around any particular plant.

Q: How can I tell if my perennials need to be divided and when should I divide them?

A: Most perennials can be divided after flowering, but I'd wait until the scorching summer weather is past. It's not a good idea to stress any plant when it's already stressed by the weather. In general if you're happy with the way your perennials look, you don't need to divide them. But if the flowers appear smaller than usual, or if they are getting leggy, falling over, or the foliage looks somewhat sparse, it's probably a good idea to divide them.

For information on dividing specific perennials, it's best to consult a gardening book or local nursery. Some plants are particular about when they are divided and may have special planting requirements.

Q: I have some spring-flowering bulbs that never got planted last year. Can I still plant them this fall?

A: It's not likely that bulbs from last year will still be good this year for planting. Bulbs should be firm, not at all soft, or they will rot. If there is any sawdust-like debris with the bulb it could indicate insect damage.

Continue to send your gardening questions to Fossil Creek Current columnist Kathy Hatfield at ocwildflowers@frii.com.