It’s not just people and pampered housecats that benefit from a warm blanket in the winter, plants appreciate one too – especially those that are adapted to gentler climates.  This past spring, we witnessed some surprising plant survival stories as a result of the protective blanket of deep snow that persisted through most of last winter. In my yard, parsley and gladiolus returned for an unexpected repeat performance. There’s still time to prevent cold injury to marginally-hardy plants, using a man-made version of the “blanket” principle, since we can’t count on a continuous cover of deep snow like last year’s. The easiest and cheapest method is to rake up some oak leaves and use them for insulation. Oak leaves are preferred because they are sturdier and have less of a tendency than more delicate deciduous leaves to pack down over time.  An old-fashioned nurseryman’s trick is to fill a peach basket with oak leaves, turn it upside-down on the plant to protect, and weigh it down with a brick or stone placed on top. Obviously, this will only work on plants small enough to fit under a peach basket. I’ve overwintered a rosemary plant in my Zone 6 garden for more than 10 years using this method. Now that the plant is large, I surround it with a hoop of chicken wire and simply fill the hoop with oak leaves. This variation will accommodate larger perennials and small shrubs, buying you protection a full zone warmer than where you are.

Fall-planted evergreens wrapped for winter Photo: U of Minnesota

Wrapping larger plants, such as fig, with insulating material (burlap or other fabric) will help them survive the winter in the milder areas of the state (Fairfield County and the Connecticut River Valley). Wrapping is also a good practice for evergreens that were planted in the fall or are exposed to windy sites; both conditions make these shrubs vulnerable to winter desiccation.  Avoid plastic as a wrap material; it can create a greenhouse effect on sunny days which could cause the plant to lose dormancy, making it vulnerable to cold damage. To avoid this, protection must be removed toward the end of the winter while the weather is still cold. It may be necessary to replace the covering quickly if late, extremely cold weather is expected.

An easier option may be to grow marginally-hardy plants in a container and once they’re dormant, move them into a garage or cellar with a temperature consistently close to freezing. Occasional light watering is the only care necessary until it’s time to move the plant back outside in the spring. Oleander and geranium (Pelargonium) can also be overwintered this way.

Gladiolus 'Mykones' Photo: D. Pettinelli

Plants that produce bulbs, corms, rhizomes and tubers when dormant (but aren’t hardy in our area) can be stored for the winter and replanted in the spring. The most common (and rewarding) are:

Gladiolus

Loosen the soil around the base of the plant with a garden fork. This late in the season, the leaves will probably fall away from the corm easily, so a little fishing in the soil may be necessary.  Let the corms dry indoors on newspaper or screen for a few days. The cormels (babies) can be removed from the corm and saved for additional stock. Store the dried corms in paper bags or onion sacks. Label the bags and hang them in a cool, 40-50 degree dry location, away from marauding rodents, until spring.

If gladiolus is grown in a cluster, it may be worthwhile experimenting with a deep mulch of leaves for winter protection. The first year, do this with a few glads that you’re willing to risk losing.

Dahlia

Dig dahlia clumps carefully, as tubers break easily. Allow the clump to dry on sheets of newspaper or cardboard. Pack the tubers in dry sand, peat moss, wood chips or granular vermiculite. A storage temperature of about 45 degrees is ideal. Small tubers can be kept in a zip lock bag or wrapped in plastic in the vegetable bin of your refrigerator. Check periodically for rot. A dusting of sulfur will help to prevent bacteria or mold from developing.

Dahlia 'Forty-Niner' Photo: Stanford University

Canna

To store cannas for the winter, use the same process as for dahlias. Unlike gladiolas, which should be stored cool and dry, the rhizomes of dahlia and canna need to retain some moisture; they should not be allowed to dry and shrivel during storage.

Before the fierce winds of winter begin to blow, protect those perennials and shrubs that may benefit from a blanket. If the ground isn’t frozen, glads, cannas and dahlias can still be lifted. Seize the moment!

James McInnis

It’s probably obvious by now that I really like to grow plants from bulbs. This time of year some might be content dreaming about that first snowdrop braving the chilling winds or how beautiful all the tulips will be along the front walkway or even what varieties of dahlias to order. I find myself bringing forced hyacinths up from the basement to be slowly coaxed into bloom, potting up amaryllis bulbs, and finally getting around to cleaning the gladioli corms I dug up last November.

The gladioli were mostly given to me by a fellow MA Master Gardener when she and her husband pulled up their roots, sold their house and moved to a retirement community in Connecticut. I have been growing them for almost 20 years now and each time a bright salmon colored blossom unfolds, I think of her. Gladioli also adorned my grandmother’s garden. I remember visiting her as a young child and staring up at the glorious blooms on stems reaching over my head. Glads make long-lasting, vibrant cut flowers and really are pretty easy to grow.

If you want to extend your cut flower season, plant batches of corms at two week intervals. In the Northeast I begin planting them in mid-May and finish up in mid-June although you could probably keep going into July. The corms are planted about 4 to 6 inches deep. The tall ones do require staking but to minimize work for myself, I have them growing through some wire grating which pretty much keeps them upright.

At the end of the season, usually in late October or November depending on the weather, the glads must be dug up in my region. I cut back the foliage to a few inches above the corms and then lift from the ground, shaking off loose soil and just set them in a tray. Corms are rather peculiar food storage organs. Each year the old corm dies and a new one is produced. If the plants are happy they produce lots of baby corms, called cormels, and these begin to grow around the new corm. If you wanted, you could pluck the cormels and plant them in a separate nursery bed in late spring. The ones the size of a dime or larger will be less likely to dry out and die over the winter. They could be stored in a paper bag at about 45 degrees F. It usually takes 2 or 3 growing seasons for your cormel to grow into a blooming size bulb.  

Glad corms before and after cleaning. Note the little cormels on the right.

I never seem to get around to cleaning the gladioli bulbs until about now. They have been kept in the cellar in the same tray I initially put them into. Now the old corms and cormels are separated from the new one. This is done by giving a little twist to the old corm. Any remnants of the old, dried foliage are also twisted off the top of the corm. Next, they are stored in an old grapefruit sack in the basement until May. Storage temperatures in the upper 40’s to lower 50’s seem to work well.  

Stored glad corms in an old mesh bag.

The amaryllis bulbs probably could have been planted before Christmas but I never seem to get around to potting them up until now. They spend the summer outside in a shaded area of the garden and are generally dug up around the end of October. A few light frosts don’t seem to bother them. They are also laid in trays in the cellar and the leaves will die back. For years I had heard a dry dormant period was necessary for flower bud initiation but apparently this is not true for many varieties. I have seen several pots of amaryllis that are encouraged to grow year-round and still send up abundant blossoms.  I may try this one year but for now I like the dig up and forget about the plant for a while scenario.

There also has been much emphasis on leaving the top one-quarter to one-third of the bulb above the potting mix. I found this doesn’t really matter too much either and sometimes just the top of the bulb is peaking through the potting mix and it still grows and blooms just fine. The most important part of potting up an amaryllis bulb is to put it in a relatively heavy container like clay or ceramic because the blossoms are large and weighty and the whole plant may topple over if kept in a light plastic pot.

Potting up amaryllis bulbs.

My favorite way to force hyacinths is in hyacinth glasses although occasionally, I do pot some up as well. When purchasing bulbs in September for fall planting, a few extra hyacinths are purchased and the bulbs for the glasses go into the vegetable keeper in the refrigerator. A little before New Year’s, I put them in their specially formed hyacinth glasses and fill with water until it just barely reaches the bottom of the bulb which is known as the basal plate. Then these go down into the cool, dark cellar.  After a month or so, lots of white roots form and the top shoot begins to elongate. They are brought upstairs to a bright, relatively cool location and will bloom in about 3 weeks. The key to forcing bulbs is to use a thermometer, take some notes and experiment with different regions in your house. I froze and desiccated a fair amount of bulbs before coming up with ideal locations.

Hyacinths forced in hyacinth glasses and in pot.

If you enjoy seeing bulbs forced into bloom, you might want to visit the Spring Bulb Show at the Smith College Botanic Garden in Northampton, MA. It runs for two weeks beginning the first Saturday in March. For more information, check out  

http://www.smith.edu/garden/home.html.

 Grow good!

Dawn