As Fall Fades, Tips to Keep Your Garden Growing

A new crop of questions sprouts as fall changes the dynamics in our gardens.

Q My pachysandra does not grow well under our ash tree, but seems to grow fine under our oaks and maples. Is there a reason for this? -- John McCrea

A Pachysandra competes well under trees in limited sun, with the types of nutrients and water usually found in wooded areas. It obviously does not have the same environmental conditions under your ash tree as it does where it is growing well. Pachysandra prefers moist, well-drained, acidic soil high in organic material, as do many shade-tolerant ground covers. Add iron sulfate according to labeled directions to acidify the soil and mulch area with 1 to 1 1/2 inch of compost so it can begin to work its way into the root systems of both your tree and the pachysandra. In large areas without plants, lightly till the compost into soil without disturbing the root system of the tree.

While visiting Charleston, S.C., I discovered the delightful fragrance of tea olive and bought two. I lost them, purchased two on another trip and planted those against a south-facing wall. They have barely survived. I transplanted them into large containers to keep in my hothouse during winter. Is it possible to plant these in the garden and have them do well? -- Susan Pennington

The tea olive in Charleston could easily have been a variety that is not hardy to Washington winters, such as fragrant tea olive (Osmanthus fragrans). This means you will have to continue to take yours into the hothouse in winter. The species I have used successfully in protected sun and partial shade is holly tea olive (O. heterophyllus), hardy to Zone 6, which should be fine here. It's a zone tougher than its counterpart but also sports fragrant flowers in fall.

We planted several elaeagnus on our property. We love the fragrance, durability and deer resistance, but have become concerned about whether or not this shrub can be invasive. Can you provide any reassurance? -- Freda Cameron

Depending on where you have it sited, this fall-flowering, fragrant, evergreen shrub could, at some point, be fruitful, multiply and contribute to disrupting the balance of nature. When planted in partial shade it will stay smaller than if in full sun, with fewer tendencies to invade. There will still be enough flowers to produce fragrance.

According to several invasive plant lists, there are two elaeagnus considered a threat in the mid-Atlantic: Russian olive (E. angustifolium) and autumn olive (E. umbellata). Thorny elaeagnus (E. pungens), which I think is the one you have, is not listed as invasive in the Washington region. Unfortunately, this evergreen shrub is considered invasive in the southern United States (http://www.ncwildflower.org). That means it could pose a threat to native plant populations in the Washington region in the future.

I sprayed my roses weekly for black spot. They did well this summer and didn't develop a problem this season until early September. Why? -- Peggy Reaves

One reason might be that your roses have developed immunity to the fungicide you use, especially if you have always sprayed with the same material. You should alternate several fungicides to avoid the chance of roses developing immunity to a particular product. Use a systemic fungicide such as Funginex for a couple of weeks and then use a contact substance such as Mancozeb for the next couple of weeks. After that, switch to a different systemic such as Immunox for several weeks. Following this regimen might help avoid black spot for the entire season. I would only recommend this type of treatment for roses where funguses are a severe problem.

Last year we visited San Antonio. There was a small bush-type plant that gave off a minty fragrance when the leaves were rubbed. It was called a copper canyon daisy. Can you tell us more about this plant? -- Tom and Sherry Lum

Copper canyon daisy (Tagetes lemmonii), also called lemon marigold, Mount Lemmon marigold or Mexican bush marigold, is an evergreen sub-shrub that grows about two feet tall and spreads easily because ends of branches that touch the soil will root. It freezes back to the ground when temperatures reach about 25 degrees. It grows in full sun, is drought tolerant and deer resistant. Not related to daisies, it is in the same genus as common garden marigolds and a native of the Huachuca Mountains in Arizona. Copper canyon daisy blooms in late fall, producing a mass of bright yellow blossoms when there is enough precipitation.