HOUSEPLANT STRATEGIES

I brought a potted lemon tree from Virginia a year ago. Last winter, I kept it near a window, where it got ample afternoon sun. By spring, it began turning yellow and lost most of its leaves. It has been outside all summer and grew nicely (even producing lemons). How can I keep it healthy this winter?
CRISTINA STEELE
Manchester, New Hampshire

If possible, place the tree in a south-facing window, where it will get maximum sun. During the winter, homes can be so dry as to border on desertlike, so try to increase the humidity levels around the plant. One method is to place the pot on a tray lined with pebbles and filled with water, which will evaporate and raise the humidity around the plant. Running a humidifier will help keep both the lemon tree and you from feeling too dry. Or spritz the tree with water several times a week. You can also place the pot in the bathroom while you shower.

Keeping the room temperature above 60 degrees will help the plant absorb nutrients and maintain active growth. Water thoroughly when the soil appears dry and feed every other week with a solution of 1/2 teaspoon of fertilizer to 1 gallon of water. Lastly, keep the tree in a clay pot. This porous material will allow air to get to the root zone.

I have had very little luck maintaining any kind of palm plant. The plants are in a semi-sunny corner that has south and east exposure. I water them when they seem dry, but within a few months, they turn brown and die.
LISA MCDONALD
Norwood

Your light level is probably not the problem (unless you have a date palm, which requires bright light). If you purchased your palms at a mass-market outlet, which tend to use inferior potting mixes, repot using a mix with a sand component. (Try an African violet mix with sand added.) Do not use beach sand, as that will raise the salt level.

If only the older fronds are turning brown, this is a natural process. Use a sharp knife to trim them off. If just the tips are browning, the plant either needs more water or is reacting to fluoride or chlorine. A switch to rainwater or filtered water should help. Also, try to increase humidity around the palm by using the methods described in the previous answer on lemon trees.

Finally, check the fronds for pests. Look for brown disks (an insect called scale), woolly patches (mealybugs), yellow specks and webbing (spider mites), and black or brown patches (fungus). A Google search should yield several websites offering advice on combating these pests.

Our 5-foot-tall cactus has been kept outside all summer, and it's doing beautifully. How should we plan to winter it over?
BONNEY SOLOMON
Braintree

If the cactus has been outside in full sun all summer, you'll need to acclimate it to lower light conditions before bringing it indoors. Gradually reduce the amount and intensity of the light it experiences (fall's waning days will help with this). When you bring it indoors, place it in a south- or west-facing window for maximum light exposure. If your natural light is limited, supplement with artificial light. Use fluorescent rather than incandescent bulbs, since they provide more of the green and blue light that plants prefer. Fluorescent bulbs also give off less heat and are more energy efficient. If possible, supply 10 or more hours of light each day.

I have some plants that call for "full sun-partial shade." What is a good location for them? How many hours constitute full sun?
JOANNE PRENDERGAST
North Andover

Full sun means about eight hours or more of full-on sun. An garden bed in the middle of a lawn or a roof deck gets full sun. So does the southern exposure of a home that is not shaded by trees or other structures.

An eastern exposure receives morning light and afternoon shade, vice versa for western exposures. This combination is called partial sun (or partial shade or light shade). Western exposures receive more intense light than eastern exposures, which affects the amount of water plants need. Plants subject to the moving shadow of a tree or building are also considered to be in partial sun. Northern exposures receive little, if any, direct light and are considered shade, as are areas under a tree's canopy.

Your plants can be planted in most eastern, southern, and western exposures and fall within the full-sun to partial-shade range. The angle of the sun changes with the season, so that a spot with partial shade in spring may move out of the shadows at the height of summer.

My perennial garden needs soil revival. My heliopsis is covered with red aphids, my astilbe is dwarfed, and my hosta are not as vigorous as usual. Should I add manure or compost this fall or forget about the garden until April?
SUZANNE O'BRIEN
Essex

It's not too late to add compost. In fact, adding it in the fall will give you one less thing to do next spring. Spread a 1- to 2-inch layer of compost or manure around the garden bed and cover with a mulch of dried, chopped leaves. Over the winter, soil organisms will slowly break down the compost. You can postpone the work until spring, at which time you can work the compost into the soil with a hand rake.

Outside the planting season, I have trouble finding plants sold in six-packs. I'm especially interested in getting herbs to grow indoors this winter.
NANCY PIERCE
Carlisle

Papa Geno's Herb Farm (papagenos.com), an online plant retailer based in Nebraska, doesn't sell six-packs, but it does offer herbs in 2-by-3-inch pots from mid-March to mid-June, the typical plant shipping season, and again from Labor Day until Christmas. It is difficult to find online seedling and plant sources at other times because it is either too hot or too cold to ship live plants.

One alternative is to ask a local nursery if it will grow a special order of the herbs you want. Or try growing herbs yourself. Basil, cilantro, chives, and oregano can be grown from seed in a sunny window or under a fluorescent light. Other herbs, such as rosemary, are grown from cuttings placed in moist soil or sand to encourage root growth.

Ellen C. Wells is a horticulturist and garden writer in Boston.