I have an Agapanthus in a pot in my garden. How can I winter it over in the house? What can I expect of it when it is in the house? Since my garage is free standing and unheated, it is cold in the winter, so it is not a good option. Help!

There is no difficulty in growing this plant as long as you can move it to a frost-free room in winter, keeping the temperature no colder than 40 degrees and no warmer than 60 degrees. There, it will need very little water until spring, when it should then be brought back to a well-lit spot and started into growth by watering and feeding. Do not repot frequently as this plant blooms best when it is pot-bound.

I planted Heliotrope in mid-June in an area that is dappled shade in the morning and full sun in the afternoon (approximately 4 hours). Even though they are only about 12 inches tall, many of the plants are flopping over and the stems seem really weak. Overall, the plants look relatively healthy, although a few have browned edges. What is causing this floppiness?

Generally, heliotrope enjoys at least 5 to 6 hours of sunlight per day. Try cutting your heliotrope back about 6 inches to promote lower, sturdier growth. You will delay flowering for 2 weeks, but the plants will benefit greatly.

As bulbs finish blooming, I know that you are supposed to leave the dying foliage and not cut it off. What about perennials? Some spring and early summer-blooming perennials start to look tired by mid-summer; can you shear off their scraggly foliage?

Yes, you can trim back perennials, but don’t trim those that can give you winter interest in your landscape. Many perennials can be trimmed or deadheaded and will rebloom, while others die back naturally, like poppies and bleeding hearts. Leave the pruners in your pocket and enjoy Sedum, Rudbeckia, coneflowers, Astilbe, and ornamental grasses all winter long. In the winter months, the grasses will add texture and sound to the landscape and the others mentioned have lovely flower heads. If you must prune them, bring them indoors and make lovely arrangements for your home.

Since many houseplants enjoy being outdoors for the summer, I brought a Norfolk Island pine outside to a sunny spot and watered it consistently. A couple weeks later, the branches and needles were almost completely browned. Was this because of too much sun or doesn’t this plant like being outdoors?

Bringing your houseplants outside for the summer can be very good for them but the correct sunlight is important. Understand that full sun indoors is about the same light conditions as shade outside. It is wise to keep your houseplants in a shady area for the summer so the foliage will be lush and the acclimation back indoors at summers’ end will be much easier.

Are there any ornamental grasses that will grow in partial (dappled) shade?

Most grass varieties prefer to grow in the sun, however you’ll find several that will prosper under partially shaded conditions. Remember that the plants might lose a bit of height, leaf color and flowering due to the shade, but these varieties will certainly grace your garden with their wonderful textures and motion:

• Sedge, Blue (Carex)
• Sedge, Golden (Carex)
• Northern Sea Oats (Chasmanthium)
• Hakonechloa
• Japanese Blood Grass (Imperata)

I have a paving stone walkway in full sun. Currently, there is gravel between the stones and I want to replace it with plants. Which ones would creep along a little, but not too much, be very low, and be able to take a little foot traffic? Also, any planting tips?

When searching for the perfect groundcover that does well in full sun, is low-growing and can stand some foot traffic, our choices are, unfortunately, extremely limited. Many sun groundcovers are low-growing, like certain varieties of Sedum or Ajuga, but they are not tolerant of foot traffic. Then, there is lilyturf (Liriope spicata). It does well in sun or shade and is content with being trampled on, but it grows to 12 inches — too tall to plant between stepping stones.
The happy medium? Thyme! This wonderful, perennial herb loves full sun, is low-growing and can take a moderate amount of foot traffic. In addition, as an added bonus, thyme emits its well-known, delicious fragrance and stepping on the plant only stirs up more of the luscious scent.

Any of the thyme varieties will perform wonderfully for this situation, creeping along slowly but surely. Lemon thyme, red thyme, woolly thyme and many more varieties offer a diverse range of foliage colors and textures, not to mention interesting variations of aromas. Don’t forget to pick a few stems for your homemade spaghetti sauce too!

When planting thyme, choose a well-drained, full-sun location. Believe it or not, thyme does its best in poor soil. Very little maintenance is necessary to be successful with it. Try not to wet the leaves when watering as this deadens their wonderful fragrance and be sure to mulch in the winter to protect the plant from heavy frosts.

I want to plant a yucca in a container that will stay outdoors all winter. Can I use regular container potting soil? If not, what type should I use?

Container gardening for perennials and small ornamental shrubs is growing in popularity, but not without problems. The greatest challenge is overwintering. In winter, the temperature of the soil in the ground stays much warmer than the temperature of the air. In some cases, up to 40 degrees different. The problem with container gardening is that the roots of the plant are elevated above the warm earth, and the cold air quickly drops the temperature of the soil in the container below what happens naturally in the ground. This usually kills the roots of the plant and leads to a disappointing spring.

Yucca has been designated as a zone 4 plant, or able to withstand a low temperature of -20 to -30 degrees Fahrenheit if planted in the ground. If planted in an above ground container, the roots will most likely die if the soil temperature drops below 10 degrees Fahrenheit. To be successful, controlling the temperature of the root zone is the key. Even if plants are in the ground, soil temperature is still important. That is why so many gardeners swear by a good overwintering mulch. The mulch helps insulate the ground from extreme temperature changes, especially those cold January nights.

Regular container potting soil would be recommended. Be sure to fertilize as needed.

I have a Lonicera ‘Dropmore Scarlet’ vine that gets about 4 hours of sun a day. I noticed that the top of the plant was covered with masses of tiny, white insects. Starting at the bottom of the plant, the leaves had all browned and fallen off. What is the insect and what should I do?

The insects on the new growth and the brown leaves at the bottom may not be related cause and effects. The insects you are observing on the new growth are no doubt aphids. Aphids love honeysuckle and are often found on the new growth causing malformed, rolled up foliage and twisted stem growth. Since they tend to cluster on the tips (and have distorted the new growth anyway), trimming them off is often an effective control strategy. Introducing lady bugs as a natural predator also works. Chemically, a systemic insecticide such as Orthene does a good job, even though the rolled up leaves may protect them from direct spraying.

The brown leaves at the bottom are due to something else. It could be due to insufficient sunlight (honeysuckles do best in full sun) or lack of fertilizer (a balanced 10-10-10 will normally do the trick). If you noticed the leaves with a dusty, white coating before they turned brown, the cause may have been powdery mildew. Honeysuckles, particularly those in shaded locations, are quite susceptible. “Remedy,” a new fungicide from Bonide is quite effective in the control of mildew. It is safer to use and not as harmful to the environment as many of the other fungicides.

What is meant by the term “tissue culture”?

In its simplest form, tissue culture (also known as micropropagation) is a technique of plant propagation whereby plants are started from very small pieces under aseptic (sterile) conditions usually on an agar-based medium. Plant parts as small as tiny stem tips, nodes, embryos, seeds or pollen are placed on a special culture medium. The nutrient medium used may vary considerably depending on the growth requirements of the specific plant grown. By varying the medium content, the plant part may be caused to produce undifferentiated callus tissue (which may be further subdivided later on), multiply the number of plantlets produced, grow roots or multiply embryos.

Tissue growing techniques allow gardeners to propagate large numbers of specific clones in a relatively short time in a small amount of space. These techniques can also be useful in producing pathogen-free plants. Tissue culture techniques are widely used by orchid growers and other members of the greenhouse and nursery industry.