Prepare Tender Plants for Winter
Winter Protecting Tender Perennials and Shrubs
Preparing tender perennials and shrubS for winter iS very important. First be sure they have received proper fall watering and fertilizing, see Preparing Plants for Winter
Protecting Tender Perennials and Shrubs
When considering tender perennials, as well as tender shrubs, for your northern or midwest garden it is important to understand the preparations required for winter. A plant is considered tender if it is not fully hardy in your zone, or may not be recommended for your zone at all. Look for information on the garden tag such as "hardy in (your zone) with winter protection". What that winter protection is generally is not on the tag, so a little research may be required. Your garden center staff should have some basic information, and often some very good tips. Extra mulch or compost mounded around the base of the plant may be enough. Some will require up to 8 inches of soil mounded at the base. A little creativity and experimentation will often produce excellent protection methods. As in the photo above, mulching material covered and held in place by a porous (will let in air and moisture) covering is the primary objective. For the covering use burlap, canvas or any porous fabric like material. Never use polyethelene sheets, it will suffocate your plant. Soil mounded up several inches at the base of the plant first will add more protection. It is not advisable to select a plant more than one zone away from yours. Survival chances are diminished.
Cold climate gardeners, being resistant to adhere to their zone recommendations, have been quite successful in getting favorite plants through winter. Zone 4 gardeners have been growing hybrid tea roses, Butterfly Bush, Rose of Sharon, and several varieties of Hydrangea like Nikko Blue, as well as many of the less hardy rhododendrons for years. The success often depends on the severity of any single winter, but with proper protection, the roots are preserved to grow anew. Plants should be heavily mulched to ensure the roots are protected whenever you plant a shrub or perennial not quite hardy for your zone. In regions that drop below -38 degrees, further protection is advised, treating the plant almost like a hybrid tea rose. And as mentioned above, mound several inches of soil at the base of the plant, and mulch heavily
Butterfly Bush blooms on new spring growth, so mounding soil at the base and heavy mulching will be enough protection to preserve your plant. The plant dies back nearly to the ground each year in zone 4 and north anyway. Spring will bring a whole new plant if the roots and crown are adequately protected. This method will work well for nearly any tender perennial.
When it comes to flowering shrubs, the same protections are generally successful if the shrub flowers on new wood. If they shrub forms flower buds on old wood in summer or fall, the possibility of success is diminished. The flower buds are not always evident, but they are there. The plant should be covered with mulch right up to the tips of the branches. The easiest way to do that is usually by forming a chicken wire cage around the plant. Then fill it to entirely cover the plant with leaves or other mulching material. Soil mounded at the base of the plant will give you added protection to the roots. You can use this method for Rose of Sharon, Rhododendrons, tender Hydrangea, as well as tender perennials.
Protecting larger shrubs and trees that bloom on old wood is more challenging due to size. It is difficult to build a large enough structure to protect an entire plant that grows beyond 2 or 3 feet. If you are determined to try a tender shrub or tree, be prepared to lose it. However, there are a few things you can do to help. First, select a planting site that offers some protection. Planting on the North or East side of a structure or screen of tall evergreens or a large tree will protect your plant from winter sun and wind. But be sure the site will allow enough summer sun. Planting close to a heated building will provide a warmer micro-climate, but beware of sun reflection from light colored surfaces. And sometimes to get close enough to the warmth, your large shrub or tree will be quickly overgrown for the space. Only a healthy plant has a chance of survival. Give the shrub or tree perfect growing conditions (proper soil, drainage, sun, water and fertilizer). Do not fertilize after mid August, and water thoroughly in fall, gradually decreasing the water in September to allow the plant to naturally prepare for winter. And take heart that if you can properly protect a young shrub or tree until it is well established, many will begin to acclimate to its’ growing conditions. If it adapts and thrives, your attention was worth the effort.
Also see additional winterizing information for perennials - Tucking in for Winter. And for detailed information about protecting roses, see Winter Protecting Roses.