Regional Growing Guide: New England
New England's erratic winter and spring temperatures, which might shift more than 50 degrees from one day to the next, can exact their toll on roses. Savvy gardeners winterize their plants by covering them with mulch, then wrapping them in woven mulch cloth or burlap to protect from both the cold and drying winds. The wraps come off in spring, and by June, the roses are in full bloom. Intense heat during July and August may slow down the plants, but they will bounce back with renewed vigor in September. Many of the most successful roses are new landscape roses and floribundas that are cold hardy and resist black spot and mildew.
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Overwintering Potted Roses
If you've ever been enchanted by a beautiful, but less-than-hardy rose variety, don't despair. You can grow tender roses in containers and overwinter them in a sheltered place. Here are some techniques for bringing your potted roses to the other side of winter.
Readying Plants for the Big Sleep
Treat potted roses like any other roses in early fall. Stop cutting flowers and let the hips form. This signals the plant to slow down and prepare for winter. The cell walls thicken to protect against winter injury, but all you'll notice is the stems turning purplish and the leaves dying. In late fall, pluck any remaining leaves - every single one - from the plant and remove any leaves and debris from the soil. Old leaves can harbor disease and insect eggs, and those left on the plant can cause increased moisture loss at a time when it's not easily replaced.
Some experts recommend spraying the branches with a dormant oil spray or a fungicide. You can mix your own mild fungicide solution of 1/3 cup baking soda in 1 gallon of water.
Keeping Plants Cozy
Since you'll be wrapping your potted rose in a cocoon of sorts, a little pruning and branch shortening will help. Remove diseased, damaged, and crossing branches, and cut back long canes to a manageable length. Then bring the pot into its winter quarters -- a shed or garage where temperatures remain cold but not arctic. In an ideal situation, temperatures wouldn't drop below 20 degree F.
To wrap plants, use burlap or sheets or even plastic bubble wrap. If you're using a burlap bag, set the pot inside it and stuff the bag with leaves or straw. Wrap the branches separately with more burlap or a sheet, securing it with staples or twine. Then stuff straw gently around the branches.
Don't try to make the cocoon too tight because roses are prone to rotting and fungal disease if they don't have adequate ventilation and drainage. The goal is to insulate the root zone within the pot (highest priority) as well as the branches. Leave an opening in the wrapping so you can reach in to check soil moisture and add water as necessary. Check if temperatures rise above freezing or at least a couple of times during winter.
Since cold air settles near the floor, raise your pot up on a table or place it inside another larger pot or planter. An empty half barrel provides ideal protection.
Burying Pots
If you don't have a good winter shelter, you can overwinter potted roses outside. In fall dig a hole in the garden that will accommodate the pot. Make sure it's not in a low spot where water and cold air settle. Submerge the pot in the soil, cover the crown of the plant with about a foot of wood chips, then cover that with straw. You can also use other protective enclosures, such as chicken wire cages, just like you would with in-ground roses.