It’s (Nearly) Fall: Which Plants Can You Bring Inside?

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Apologies to the Clash, but it’s time to decide: Should it stay or should it go now? From the canna planted by the corner of the porch in spring to the hanging basket of petunias perched nearby, many plants that provide seasonal garden color aren’t winter-hardy. But can we bear to simply compost them when frost arrives?

Dennis Schrader is a veteran plant-stasher, with an inventory of some 1,600 kinds of tropicals, unusual annuals and more, carried over year to year. That expertise — knowing which to overwinter as seed, cuttings or houseplants, and which to keep dormant in the equivalent of a root cellar, and at what temperature and humidity — is at the foundation of Landcraft Environments, Ltd., the wholesale nursery he and his husband, Bill Smith, founded in 1992.

They began the Mattituck, N.Y., nursery because Mr. Schrader couldn’t find the unusual plants he wanted for the design-build landscape business he had at the time. So they started propagating the plants themselves. One home greenhouse eventually begot a farm, and many more.

So should gardeners bother trying to save the plants they’ve been laboring over all summer or just buy replacements come spring?

“There are some that are really worth keeping, because they just get better with age — like a Brugmansia,” he said. “Or bulbs like elephant ears, cannas and dahlias that get bigger or multiply.”

ImageBrugmansia, or angel’s trumpet, such as the variegated variety Sublime, gets bigger and better with age. Store it for the winter at about 40 degrees, without cutting the plant back first.  
Credit…Landcraft Environments, Ltd.

The mad stash in various forms is underway at Landcraft, which supplies garden centers, landscapers and public gardens. Seed-laden flowering stems are being snipped and piled in aluminum roasting pans to bring inside and dry. Hefty stock plants that will offer up late-winter cuttings for 2021 are already in the greenhouses.

Each species has particular overwintering requirements, and they may not match conditions that you can provide. But Mr. Schrader suggested some strategies to try — and offered some tough love (gulp!) on what to say goodbye to.

Credit…Landcraft Environments, Ltd.

True annuals — plants that go from seed to setting seed in one growing season — are good beginner candidates for seed-saving, Mr. Schrader said.

A disclaimer: Hybrid varieties (including some marigolds and sunflowers) won’t produce offspring identical to the parent. So research whether your variety is open-pollinated — and if not, enjoy the surprise.

Some familiar candidates: morning glory and moon vine (Ipomoea), Nicotiana, Gomphrena, Celosia, amaranth, sunflowers (Helianthus), zinnia, cosmos, cleome, calendula, marigold, Verbena bonariensis, annual forms of poppy and larkspur, and certain Salvia, including Lady in Red and Victoria. (You can also save vegetable seed; more on that here.)

Timing is everything, so sharpen your powers of observation, Mr. Schrader said, and watch the weather. Collect from totally dry plants, not those soaked by recent rain.

The goal is always ripe seed, but what is ripeness in one species versus another?

“It’s almost always about nuance,” he said.

If the plant forms a pod, it will eventually split open and disperse the seed. On Nicotiana, for example, the little pods on the flower stem discolor from green to yellow, then tan, then brown. Brown would be very ripe — meaning the tiny seeds may have spilled already. Too late.

With a zinnia or marigold, seed forms in the fading flower’s base, “so when its petals are falling, it’s getting to be time,” he said. “Split a couple open and see.”

Let the collected seed dry for a few days to a few weeks, then store it in a cool, dry and dark place, in labeled baggies or envelopes. Check it occasionally to make sure grain moths haven’t gotten in, and for signs of decay.

Credit…Landcraft Environments, Ltd.

While it’s tempting to carry annual pots indoors for winter, it’s often better to take cuttings. Try this with coleus, sweet potato vine (Ipomoea batatas), Impatiens, Alternanthera, Tradescantia, either rhizomatous or cane or wax begonias, and ornamental sages, including Salvia leucantha.

“Get out there well before a frost and start taking cuttings,” Mr. Schrader said. First, pinch off any flowers or buds. The length of the cutting depends on the plant, but should average two to three inches.

Often, the bottom set of leaves will need to be removed. Some — like coleus and sweet potato vine — root readily in water, but a cell pack filled with potting soil is better. Let the cuttings sit overnight before sticking them in the medium, with the lowest node below the surface. Rooting hormone can also be used. A bright, warm spot hastens success; you may want to call your seed-starting lights into service.

Mist regularly or, better still, put a plastic bag over the cell pack to make a mini-greenhouse, which will reduce wilting and protect the cuttings from drafts. Snipping large leaves in half crosswise also reduces moisture loss.

“Don’t worry if cuttings wilt by day,” Mr. Schrader said. “At night, they’ll perk up and get more turgid. Then, suddenly, they stay upright all the time, a hint that they’re starting to root.”

Fast-rooting cuttings like coleus and sweet potato vine can be potted up to larger quarters, pinched and shaped to use as your own stock plants, to take more cuttings from in late winter.

Credit…Landcraft Environments, Ltd.

Tender plants grown from underground, bulb-like structures will require a rodent-proof, frost-free storage space that is cool (about 40 degrees), dark and not damp — as well as your openness to experiment. Cannas, dahlias, gladiolus, calla lilies and pineapple lilies (Eucomis), and some elephant ears (Alocasia and certain Colocasia) could overwinter there.

Not all cellars, garages or exterior bulkhead doors are created equal. Learning how cold yours gets, and how dry or humid, may involve some mishaps — not unlike figuring out where best to store that garlic you harvested in July.

Wait until a hard frost wilts the aboveground parts, signaling the bulb below to shut down. Then cut the plant back to the ground and dig carefully, starting maybe a foot from the stem. A pitchfork or digging fork is less invasive than a spade, Mr. Schrader said. And if you grew more than one variety of any of the above, be sure to label them carefully.

Lay the plants in an airy spot out of the sun for about a week. Then stash them — in milk crates, plastic laundry baskets or even net bags, which are good for hanging gladiolus or dahlias. Some gardeners separate bulbs that form big clumps into smaller ones before storing them; others wait until winter’s end.

Mr. Schrader recommends wrapping bulbs in newspaper to store, or nestling them in beds of shredded newspaper, or in bark or wood-chip mulch. Spraying newly dried bulbs with an anti-desiccant can also help preserve them.

Easiest of all, probably, are cannas. Dahlias can shrivel if they get too warm and dry, or become moldy if they get too damp, so store them in the bark or wood-chip mulch, and check on them every couple of weeks, misting lightly if they seem dry and discarding any that show decay.

Credit…Margaret Roach

Maybe the easiest holdovers are those you can treat like houseplants, including non-hardy ivy and ferns, Plectranthus, elephant ears in the genus Alocasia, cane-type angel wing begonias, Tradescantia and flowering maple (Abutilon).

Don’t feed them in winter, Mr. Schrader said, and allow the soil to dry a bit between waterings: “You don’t want to push active growth, but rather to match your care to the reality of shorter days and lower light.”

Check incoming plants for insects, or a slug curled up in the pot’s drain hole.

Another piece of advice: A phased approach over a couple of weeks is easier on a plant than being left outside till near-frost and then suddenly being brought into a dry, heated home. Houseplants summered outdoors dislike quick transitions, too.

When arranging plants by a window, remember Mr. Schrader’s aesthetically counterintuitive advice: Put the short ones closer to the light, so the taller ones don’t shade them.

Credit…Landcraft Environments, Ltd.

Don’t torture that geranium (genus Pelargonium) by asking it to keep growing. Various tropical plants have a natural dormant period, Mr. Schrader said: “Even in a lush rainforest, there is sometimes a dry season.”

Let the Brugmansia or angel’s trumpet nap, too, along with that tropical hibiscus or tuberous Begonia boliviensis.

With fancy-leaf geraniums like Vancouver Centennial or Crystal Palace Gem, “cut off any flowers, but leave them as is, in their pots,” Mr. Schrader said. “Then put them somewhere dry and dark and cool to rest — around 40 degrees.”

Don’t cut back woody plants like Brugmansia or hibiscus first either, he said: “Let winter do its damage, then clean them up when they come out of storage. If there is dieback and you already cut it back, you could have nothing.”

For non-hardy plants with high light requirements and those inclined to insect infestations or otherwise likely to sulk in human-contrived environments: To the heap with them, an exercise in letting go.

Sadly, those petunias and Calibrachoa are on the list that should go now, Mr. Schrader said, as is heliotrope, Bacopa, Lantana and Fuchsia — and also that current darling creating a silver waterfall effect cascading over many a pot rim, Dichondra.

With all of them, he is pragmatic. “I’m not saying someone hasn’t succeeded,” he said, “but … I think buying a new one next year will be easier.”

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