Garden Doctor

from Garden Doctor Q & A
Get gardening questions answered, such as how far apart to plant perennials to understanding how much sun your potted azalea needs.

Grow morning glories

Q: I would like to plant morning glories along a wood fence. Where’s the best place to put them? What care do they need?

Long Island, New York

A: Morning glories need a spot in full sun; if there’s too much shade, they won’t bloom. Water them throughout the summer to encourage lots of flowers. Don’t fertilize them much unless you have very poor soil — too much fertilizer encourages leafy growth at the expense of blooms.

In areas such as yours that experience short summers, start your morning glory seeds indoors a month or two early. Most of the season can pass before morning glories grow large enough to bloom; many a gardener has grown them only to see a small handful of blooms before autumn frost kills the plant.

Forced azalea

Q: I received a potted azalea. I’ve kept it outside and it’s doing well. I’d like to transplant it into my yard. I know it likes acidic soil, but I don’t know how much sun/shade it needs.

Huntsville, Alabama

A: Different types of azaleas are sold by florists as gift plants. These azaleas require well-drained acidic soil (around 5.5–6 pH) and partial shade. While well-drained soil is a must, they appreciate good moisture — keep them from drying out, especially in times of drought.

The plant should be fine outdoors in your climate, as most florist azaleas are hardy only in Zones 7–10. Gardeners who live outside that range will need to treat the plants as annuals or short-lived gift plants.

Perennial parameters

Q: How do I know how far apart to plant my perennials?

Hilton, New York

A: You are right to take time to learn to properly space your perennials. For a modest investment up front, perennial plants will bring years of color and interest to your garden or landscape. A little time and effort spent in proper planting will pay off in the future.

I recommend you consult a good book on perennials before planting. One of my favorites is Manual of Herbaceous Ornamental Plants by Steven Still. You will find information about spacing as well as soil, sunlight, and water needs.

If you are planting nursery-grown plants, refer to the label. The preferred spacing is usually a range, such as 18–24 inches. Planting closer will give you a fuller garden sooner, but you will probably need to divide the perennials sooner. Plants with closer spacing are more susceptible to fungal diseases caused by poor air circulation. Most perennials benefit from division after three to five years.

If you can’t find information about a specific plant, a general rule is to space small perennials 6–12 inches apart, 2- to 3-foot perennials 12–18 inches apart, and taller perennials 18–36 inches apart.

Expanding horizons

Q: My new perennial garden has growing bigger than I thought it would and I need to move some plants. When is the best time to do this?

Huron, South Dakota

A: It’s great that your new garden is doing so well that you already need to expand. You must truly have a green thumb!

Most perennials are best moved in early spring, just as they break dormancy. Try to transplant on an overcast day, and get plants back in the ground as soon as possible. If you must leave them out of the soil for a day or two, dig them with some soil around their roots, sprinkle them with water, and place them in a shaded spot until you can get them back in the ground. Plants that will be out of the ground for more than two days should be potted in nursery containers and kept well watered until they can be replanted.

A few perennials are best divided in late summer. This list includes peonies, iris, and daylilies. If you move them in the spring they might not bloom that year.

Eliminating grass

Q: I want to add a mulched cutting garden to my yard. I’ve read mixed reviews on the use of fabric weed barrier. I have a large birch in this area, which I do not want to use. I am concerned that the weed barrier will limit the water to this tree.

Perkasie, Pennsylvania

A: I’ve had bad experiences with fabric weed barriers because weeds can grow on top of them. These weeds are difficult to pull because their roots growth through the woven fabric. The product can be difficult to remove, especially once soil accumulates on top of it.

If you use the weed barrier, your birch should be fine, especially if you mulch over the fabric to conserve moisture.

My favorite technique for killing grass is laying down a 5-sheet-thick layer of newspaper, then mulching over it. As the newspaper decays, it improves the soil's structure, which is especially helpful if you garden in sand or clay.

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