One of the biggest issues plant growers face across the country is that of a hard frost. No matter the kind of plant, location, or time of year, frost can wreak havoc on crops, limiting the growing season and potentially causing plants to die if not handled correctly. Can you, and should you, cut back perennial plants before a frost?
You shouldn’t cut back perennials before a frost. Since perennial plants come back in the following years, they undergo their own kind of hibernation during the winter season. If the plants are cut back before they enter this period, they will try and regrow, causing them to have less energy.
Understanding when and how to care for your perennial plants is essential in ensuring they will be successful coming back in subsequent years. Read on to learn more about handling perennial plants, including how they differ from other plants, their dormancy period, why frost harms plants, and how to handle perennials during a frost.
Perennial Plants Explained
As a little kid learning about the seasons, you probably wondered at some point how trees didn’t die in the winter. They lost all of their leaves, and looked dead, but every year during spring, these same trees would come back to life. Why? It’s not like trees can go into hibernation like a bear can, move to another location like birds, or stay inside like people. These trees are stuck outside throughout the winter season’s snow and ice but come back to life each year.
Most trees belong to the type of plants known as perennials. Perennial plants are plants that survive continuously through multiple growing seasons. When you plant your garden during springtime, there are certain plants, such as petunias, that you need to replant every year. These plants can’t survive the winter and are confined to an annual lifecycle.
Perennials are plants that will naturally come back in the spring. These include plants like roses and tulips.
To the untrained eye, identifying perennial plants in the fall and winter can be difficult. During these cold seasons, the plant shrivels up and seems to die. It looks no different from any other plant. This is because, during this time, most of the plant is dead. Perennial plants retreat underground during the cold months. Imagine that all of your limbs died off during the winter, but your heart was still alive. This situation is similar to what perennial plants undergo.
Of course, not all perennial plants completely die off during these cold months. In fact, many stay perfectly normal. Some evergreen plants (plants that don’t lose their leaves in winter) are perennial. These plants simply don’t grow more during the winter, maintaining their current levels of life.
Plant Dormancy Explained
After understanding what perennial plants are and how they differ from other plants, you are likely curious about how these plants actually survive the winter. We know, in a very basic sense, that perennial plants often lose their leaves to save energy and the important parts of the plant, but how this process occurs is seemingly a mystery.
Fortunately, you aren’t the first person to be curious about this process. Until recently, how these plants survived was not well understood but today, scientists have a much better grasp of the concept.
Perennial plants enter into what is called a period of “dormancy” during the cold months of winter. Essentially, plants take the same approach many animals do. Since they can’t produce food this time of year, they “sleep” it off.
Over the course of the year, plants create tons of energy through photosynthesis. While they consume most of the energy they produce during this time, they store very small amounts of it. During the winter, plants stop growing and use almost no energy. As a result, they don’t need to consume nearly as much energy and can rely on the small traces they’ve saved to keep them alive during the winter.
Some plants, however, end up storing more sugar than they need. Maple trees, for example, end up having too much sap and expel some of it through holes in the tree’s bark. This sap is a sweet-tasting fluid that, when boiled, turns into maple syrup.
Impact of Frost on Plant Life
Now that you understand perennial plants and their dormancy period, it’s important to consider how frost impacts plants generally before looking at the impact of frost on perennial plants.
Frost occurs when temperatures fall below freezing and water particles in the air condense from a gas state into a solid state. This frozen moisture then rests on plant life, causing the plants to cool down drastically.
Interestingly, water is a hydrophilic particle. Similar to magnets, water likes to join with other sources of water. This means when the frozen water moisture rests upon the outside of the leaf, water from the inside will try and get as close to it as possible. This results in the water inside the plant freezing slightly. Though this is not an issue if the plant is able to thaw quickly, it can be damaging to the plant otherwise.
If the water inside the plant remains frozen for too long, it will slowly begin to expand. However, this water is trapped within the cells of the plant, meaning that the cells will need to grow. Plant cells aren’t able to expand widely, however. Eventually, when the water expands enough, it will cause the cell to break open, leading to its death.
This is why there are different “hardnesses” to a frost. If there is a “hard frost”, this means that water is frozen more solidly than in a “softer frost”. Hard frosts take longer to thaw, making the plants less likely to survive. Some plants might be able to survive a few “soft frosts”, or maybe even one “hard frost”, but they can’t survive much longer after that.
Frost and Perennial Plants
We can now move on to explore how owners of perennial plants should handle frost.
For most non-perennial plants, the goal is usually to shield them from frost, thereby extending their lives. When it comes to perennials, the approach is different. If perennials don’t go into a period of dormancy, they can die from exhaustion. When the winter months begin to approach, you want to encourage your plants to enter dormancy.
One way to do this is to allow them to freeze in the frost. When cells die from frost, perennial plants notice and understand that the cold is now here and that they should enter into dormancy. Frost acts similar to an internal clock, triggering perennials to change to dormancy. Once the plants become dormant, you can cut them back to ensure they aren’t wasting any energy trying to stay alive.
If you cut back perennials before a frost, however, the plant won’t understand what is occurring. If cut back during a non-dormancy period, the tendency is for plants to try and regrow. This takes a lot of time and energy. So, if you cut back plants before a frost, they will start to work on the regrowing process.
Unfortunately, if plants begin wasting energy regrowing when they should be entering into dormancy, they waste the energy they had saved and will not reduce energy consumption quickly enough. This will cause the plants to exhaust themselves and could lead to plant death. Therefore, don’t cut perennials back until after one or several frosts.
To appreciate how to care for perennial plants during a frost, we need to understand what they are, how they differ from other plants, and how they respond to frost.
Perennial plants use a hard frost as a signal to enter into their period of dormancy. However, if they don’t experience frost, they won’t enter into dormancy and will eventually die.
To avoid this, do not cut back perennials until after a frost. Doing so will make them tap into their winter energy reserves, causing them to die. So, wait until after a frost to cut back your perennials.