Winter Care For Your Plants

Temperatures are getting colder; soon we are likely to experience a killing frost. I generally consider that to be a cold snap below 28°F. When that happens things start to go to bed for the winter months.  We often receive many inquiries this time of year with regard to specific questions on how to prepare perennial plants such as trees, shrubs, and other flowers for winter here in ND and eastern MT.

The big one we usually remind folks of is consistent water.  Although some years there is an overabundance of moisture available we must make sure that we continue to provide that as the days go on. This should occur of course on an "as needed" basis.

Often we receive a reprieve of winter temps during the months of November and December.  When that happens we often do not receive any rains or snows that contribute to fall moisture and the ground can become fairly dry before or as it begins to harden for winter. This can be extremely dangerous for all perennial plants in our climate.

The reason for that danger is as follows.

Moist soil insulates against the cold whereas dry soil does not.  This can cause several issues for plants but I will outline two primary problems.  Firstly, when plants store their energy in their root systems, they store, at a level that seldom reaches freezing temps.  When the soil is dry and the cold can move down further than normal it can become challenging for those plants. Secondly, the dry soil does not hold temperature in the way that wet soil does. This problem becomes particularly critical in the spring of the year. When we start to see warmer temps in April, the soil begins to warm up with the heat of the sun. If the soil is dry it warms up much quicker than if it were insulated and remained cold by water and ice. When this happens many plants become tricked into thinking it is time to wake up for the year when they really should "stay in bed" for another few weeks. This can subject them to spring frosts that can be damaging to young buds or flowers. Take care to be sure that plants receive appropriate amounts of moisture up until the ground begins to freeze.

Other perennial plants such as perennial grasses, peonies, daylilies, etc., the foliage can be removed anytime after they have experienced a frost. They will not produce leaves from the leaves they grew this year. New growth will emerge from the roots in the spring. Cut the foliage down to at or near ground level.

Below I will outline some helpful tips for specific perennial plants.

Care of Roses:

Remember to allow roses to experience a killing frost of around 25°F. After this occurs you can cut the leaves and stems back to between 9 inches and one foot. Roses can and should be mulched to provide a layer of protection from the cold. Do not add any mulch until the air temps are seldom above freezing during the day. The addition of mulch too early can create a warm habitat under the mulch for mold and fungus to develop which can actually be more harmful than the cold. In general, you should wait to mulch anything until temps are barely above freezing during the day.

Care of Evergreens:

Some often contact us in the fall with concerns that their evergreens are dying because they have needles that are turning brown and falling off. This is a normal process for all evergreen plants. Even though they retain their needles all year, they do go through a period of time where they shed their third year and older needles. Often these needles have just gotten old, or they are in a location on the plant that no longer receives the appropriate light for them to be useful and so the plant sheds them. Again this is normal but usually occurs on the inside of the plant.  If you see needles that are browning from the tips back towards the stem, that is a different issue. Winterburn is a common problem for evergreens in our climate, and especially to plants that are fairly young in age. We often do not receive the snow we need to protect them from the cold and so we can consider other methods of protection. Some wrap these plants in breathable material such as burlap. You can also apply a natural chemical product such as Wilt Stop or Wilt Pruf. These natural pine resin products help to coat the needles of the plant and protect against the cold. Watch the weather with this chemical method as it generally requires a nice 50°F day to be effective. I like to see this applied sometime in mid to late November as it has a chance of lasting through the coldest part of the winter. These chemical applications are good for approximately four months and an application in November helps them last until the end of February, after which time most of our bitter cold has passed.