Hilling in, or hilling up, plants for the winter is a method of protecting tender plants over the cold winter by covering them up with a thick layer of mulch. This is a technique often used for rose bushes, but it would also be effective for any plant that needs protection from frigid winter temperatures. By using a combination of soil, leaves and evergreen boughs, you can successfully hill in your plants during the winter months.
Assess the plants prior to hilling them in and decide whether you should prune them before covering them. Trim back the plants to make them shorter, if desired. Do not perform any radical pruning at this time, however, as you don't want to make the plant think it is time to grow right before winter. Tie the branches of the plants together to keep them from blowing in the wind.
Place a layer of compost or rich soil over the crown of the plant, where the plant stem meets the roots, and the bottom of the plant. Make this layer approximately 12 inches high. It is very important that this layer be loose, loamy soil. Do not use compacted soil.
Add a 12-inch layer of shredded leaves over the first layer. The leaves should be dry and light. Cover the main portion of the plant with the shredded leaves.
Top the leaves with a layer of evergreen boughs. Layer the evergreen boughs loosely over the leaves in a 4- to 5-inch layer. The evergreen boughs may hide the plant's stems completely, or just the top-most portions of the stems may protrude. Either situation is acceptable.
Remove the mulch layers in the spring when the air begins to warm slightly. When the extreme winter temperatures are over, you can safely remove the mulch.