Trenches along with mulch provide a safe space for overwintering hardy plants

Usually by this time of year, all of our potted and otherwise loose plants are tucked away for winter. Because we had such a dry and mild November and December, we left our plants outside and in the open as long as possible.

The relatively warm temperatures and small amount of rain tended to dry them out. By leaving them out during that time, it made it easier to keep an eye on them and water if necessary.

Now that colder weather is finally here, I’ve decided it’s time to take care of the plants that we plan to overwinter. I like to wait until the temperatures are consistently in the lower 40s during the day and below freezing at night.

The overwintering process I like to use involves partially burying the plants in the garden.

This fall we have several plants that we are overwintering. There are some bare-root corkscrew willow cuttings that we started earlier in the season but will not plant out until next spring.

Also, I’m saving a potted catalpa sapling that I dug up and potted during the summer. I plan to use it for pollarding sometime in the future but haven’t decided on a place to put it.

Additionally, we have a couple of azaleas that someone had given us. They each have a developed root ball but are not potted.

We also have a small evergreen bonsai that is several years old and gets overwintered outdoors every year.

For the willow cuttings, I dug a trench in the garden where the potatoes were growing. That space is now open and free of weeds, making it an idea place to overwinter plants. The trench is about a foot deep, enough to cover the newly formed roots and much of the stem. I then laid the cuttings on an angle in the trench and covered them with loose garden soil.

Since the catalpa is potted, it was easy enough to simply dig a hole deep enough to cover the pot and about a third of the lower branches of the sapling. That way the roots and base of the plant are protected from the harshest winter weather. If the tops do get destroyed by excessive cold, there will be buds in the lower part of the stem and crown that will sprout and grow into a new plant next spring.

The bare root ball of the azalea was also straightforward. I dug an extra deep hole to place it into, much deeper than it would be for planting to protect the crown and lower part of the stems.

The small bonsai also got an extra deep hole to snuggle in over winter.

I then covered all of the buried plants with a generous layer of loose mulch consisting of a mixture of shredded leaves and straw. Most gardeners know not to use whole, un-shredded leaves for mulch. Even though they appear to be fluffy when first applied, their flat profile causes them to eventually become matted down and lose their airiness. Shredding breaks up the wide leaves and prevents matting. Mixing straw and shredded leaves makes an even more mat-resistant mulch. It is not an attractive-looking mulch, but it works well for this application.

The azalea and bonsai have leaves on them that stay on all winter. To help keep their branches from getting pressed down by the weight of the mulch and winter snow, I placed a tomato cage over them before adding the mulch. This will help to give some support to the branches.

For the bonsai I placed a thin layer of mulch over the base of the plant and over top of the pot. This will make it easier to clean off the garden soil and debris from the pot when the plants get lifted in the spring.

By being in the ground, the plants will also benefit from any residual soil warmth. As the soil warmth moves toward the soil surface, the mulch prevents it from radiating out and up into the air. If there is a deep enough blanket of mulch over the top, the soil will generally not freeze too hard during normal winters.

The combination of soil coverage and mulch acts kind of like a refrigerator keeping the plants cold and moist but not allowing them to become cold damaged.

The insulating effect of mulch also prevents alternate freezing and thawing, which can damage plant roots. It’s much better to keep the plants consistently cold through to winter.

Desiccation is another danger can happen if plants are exposed directly to dry cold winter winds; burying the plants and mulching them keeps drying out to a minimum.

For the second and into the third week of December, the weather people are predicting several dry days with daytime temperatures in the forties and lows in the 20s at night.

Why not take advantage of the weather and prepare a spot for any plants you might have left over that you may want to plant in the spring? Your plants will thank you.