The mere thought of winter, the cold days and dwindling sunlight, can send the hardcore gardener into withdrawal. It’s enough to turn a green thumb blue. But you don’t have to watch the garden’s bounty die as winter approaches. Many plants can be overwintered, or kept alive, indoors. You can also start your own seeds inside, while the cold weather lingers. Got cabin fever? Here’s the plan.
While most plants can be overwintered indoors, one thing is certain: Plants need more care than they would in an outdoor garden. Lighting, fertilizing, pollination, soil, temperature and watering all need to be monitored carefully.
You can buy plants from a local nursery, or you can move those that have been summering outdoors in for the winter. If you’re choosing the latter, check for insects, since “critters proliferate quickly indoors,” says Maggie Moor-Orth, an agricultural expert at Delaware State University. Not all bugs are bad, of course, so it’s wise to learn which are beneficial.
The first thing to consider when starting an indoor garden is how much light plants need. Some require lots of light, though most houses don’t offer enough, especially during the shorter days of winter. So if past attempts at indoor gardening have failed, look to the light, says Peg Castorani, co-owner of Gateway Garden Center in Hockessin. “One of the things we see most commonly is the selection of the wrong plant.”
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Castorani recommends selecting plants that require medium to low light. Consider ferns, palms, crotons, dracaenas, sansevierias, bromeliads, philodendrons and succulents. Herbs are lovely and fragrant, most notably basil, rosemary, parsley and oregano.
Windows that face south or west are positioned best to offer plants eight to 10 hours of sunlight daily.
If you’re low on natural light, use florescent lights, which emit little heat and won’t dry out plants. Full-spectrum grow lights are better, since they bathe plants in certain wavelengths of the electromagnetic spectrum that plants use naturally during photosynthesis. Plants grow toward the light, so make sure to rotate them to ensure upright growth.
Watering will also need to be monitored carefully. Indoor plants can fall victim to indoor heating, which means they don’t get the humidity needed to survive for long periods. Yet watering too frequently can deplete nutrients and cause root rot, especially if the plant is left to sit in water that has collected in its dish.
When it comes to watering, err on the side of dryness. If you’re not sure whether a plant needs watering, pick up the plant after it’s been watered and later, when it’s dry, then compare the difference in weight.
Lack of humidity can also affect the health of a plant. Using a humidifier can help, as can misting leaves in the morning. Andrew Olson, landscape maintenance supervisor at the Delaware Center for Horticulture in Wilmington, recommends placing pebbles at the bottom of a tray, then filling the tray with water up to the pebbles. Place the plants on the pebbles, making sure the bottoms of the pots don’t make contact with water. Bell likes to group plants around an indoor waterfall for a decorative look.
The amount of fertilizer you need depends on the type of plants you have. Because plants go dormant in winter, gardeners recommend fertilizing very little, if at all. Try diluting fertilizer to one-half or one-quarter strength and using it on a monthly basis.
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Temperature requirements vary among plants, too. As a general rule, temperatures should be between 65 degrees and 70 degrees during the day. Most plants can tolerate a 10 to 15 degree temperature drop at night.
Because cold radiates off the window after sunset, keep tender plants about a foot away from windows. Light is important, “but so is keeping plants warm,” says Nancy Bell, perennials manager at Gateway Garden Center in Hockessin.
Pollination is another challenge for the indoor gardener. Since there is no wind or insects to pollinate the plants naturally, manual pollination is required. Don’t panic—it’s not as scientific as it sounds. If you’re growing tomato plants indoors, for example, Moor-Orth suggests shaking the stake to promote pollination. If that doesn’t work, use an artist’s brush to transfer the pollen from one plant to another.
Get a jump on spring by starting plants from seeds. Seeds are less expensive than plants, and once the weather warms, plants can be easily transplanted into the garden.
A word to the wise: Don’t be swept away by catalogs hawking the seeds of glorious plants you’ve never actually seen in this region. Buy seeds that can succeed here. At burpee.com, for example, gardeners are asked to complete a profile that includes zoning information. (Delaware is zone 7.) Burpee will recommend indigenous seeds or those that will do well in the area. Read the small print on seed packages. Vegetables such as beets, beans, potatoes and corn do not transplant well, so they generally need to be sown directly into the garden.
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Different seeds have different germination and growth rates. Tomatoes, eggplants and marigolds need to be started six to eight weeks before the last frost, which in Delaware, is estimated at mid-May. Others, like impatiens, begonias and lettuce, should be started 10 to 14 weeks before that date. Be careful not to start too soon. Seedlings that spend too much time indoors may end up “weak and spindly,” says Valerie Cordrey, owner of East Coast Garden Center in Millsboro.
Though it’s important that containers are clean and offer good drainage, almost anything can serve as one, including yogurt cups, egg cartons and plastic salad bar boxes. Biodegradable peat pots can be planted directly into the soil, thus reducing any setback from transplanting.
Choose the growing medium after preparing containers. Experts recommend using a soil-less mix containing peat moss, vermiculite and perlite. Regular outside soil will almost certainly contain weeds, fungus and insects. Fill containers with soil, dropping several seeds in each, then cover with plastic wrap or domes supplied with seed kits. Label the containers and place them in moderate light. There’s no need to fertilize yet.
Try to maintain a soil temperature of 80 to 85 degrees, which can be accomplished by using a heat mat. The outer coating of the seed must get wet for it to germinate, but too much moisture can lead to mold and fungus.
When seedlings emerge with the first true leaves, remove the heat mat and plastic wrap. They’ll need more light, because seedlings require about 16 hours of bright light each day, and even the sunniest window may not meet this requirement. Placing the plants under a 40-watt fluorescent bulb or a specially designed full-spectrum grow light works best. Set lights on a timer. Forgetting to turn them on can stall growth. Once seeds become seedlings, they should be misted with a balanced plant fertilizer diluted to half strength.
Some seedlings may not appear as strong as their container mates. “Now’s the time to cull those that have little chance of making the move to the garden,” says Olson. “You need some tough love when it comes to gardening.”
In late April, prepare both the seedlings and the plants for the transition outdoors. Start by placing plants outside in a protected area, out of the wind and direct sunlight, for about an hour, then slowly increase the time each day. Watch the weather, not the calendar. Spring temperatures in the high 30s or low 40s may be OK, says Moor-Orth, “but for things like tomatoes, you want it to be around 50 degrees.” Seedlings should be planted on an overcast day or later in the afternoon. “That way, the sun won’t beat them down.”