Just about the time the soil is freezing, it is time to pile on the mulch. Mulch does not keep your plant warm through winter, it helps the soil to maintain a more constant temperature and also helps it to retain moisture. Soil that freezes, thaws, and freezes will eventually damage roots and may heave your plants up out of the soil.
Plants and perennials that require additional protection to survive your winter will need a deep layer of mulch added by mid- November or later, when the ground is beginning to freeze. Do not add deep mulch too early or your plants will not be slowly exposed to colder temperatures, allowing them to acclimate for winter. Leaves, other than oak or beech, are not recommended for mulching. They tend to mat down and prevent air from reaching the soil, damaging your plants. Grass clippings are also less effective than other mulching materials.
Certain tender perennials just can’t be resisted even in northern climates. Before selecting a tender perennial, shrub or tree for your garden, be sure to check special methods for protecting them through winter.
When considering tender perennials, as well as tender shrubs, for your Midwest garden it is important to understand the preparations required for winter. A perennial 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. Mulching material covered and held in place by a porous covering is the primary objective. 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.
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 first will give you added protection to the roots. These are common methods for rose protection. 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.