Are you ever swept off your feet by some unique, beautiful plant you spot while browsing at a nursery? You confirm that it is hardy in your zone and even thrives in your soil type! Of course, you have to buy it. You plant it in just the right spot for its sunlight and moisture needs, and baby it throughout the summer as it flourishes in your loving care. Everything seems just perfect for providing this plant with a long, happy and healthy life, right? But even though everything seems ideal, your prized purchase doesn’t make it through the following winter. Confused? You are not alone. Colorado has unique weather that can be really challenging for plants and is one of the main reasons why some plants that are hardy for our zones still struggle to survive here. Luckily, there are ways to help plants survive Colorado’s Winters.
Colorado’s Tricky Temperatures
Some plants just aren’t cut out for Colorado, but not for any reason that you can identify based on a typical plant label. Colorado is a unique environment. Our seasons are unpredictable and can be really challenging for plants, especially non-natives. We can have huge, sudden temperature fluctuations in spring and fall, as well as stretches of unseasonably warm weather in winter, both of which can confuse and trick plants. This past fall (2019) was no exception. Our gorgeous summer weather held on well into October, when suddenly not only was summer over, but apparently, so was fall! We went straight from consistently warm weather to bitter winter cold with a low of just 18 degrees Fahrenheit in less than a day. Many plants weren’t prepared for cold weather and didn’t appear to have even started the process of going into dormancy. Most plants will survive just fine all the same, however, going into dormancy “properly” gives plants a much needed advantage come spring, when unpredictable Colorado weather can wreak havoc on plants.
The Importance of Going Dormant
Why is it important for a plant to go into dormancy before its leaves freeze? Chlorophyll is the molecule that gives plants their green color. It is also the molecule plants use to convert sunlight to food and energy. When a plant heads into dormancy, the chlorophyll in its leaves is broken down into smaller molecules that can then be absorbed and stored in other parts of the plant, such as its branches. This break down of chlorophyll is why leaves lose their green color in fall.
Chlorophyll production in the spring is a high energy process. The migration of nutrients and energy from the previous year’s leaves gives the plant a head start the following spring. The plant can reuse the stored energy and nutrients such as nitrogen to push out leaves and make chlorophyll once again. Without the previous year’s stored nutrients, the plant must absorb and convert nutrients from the environment to produce chlorophyll – a much more energy consuming process! Depending on the type of plant and its health, pushing out new leaves can deplete a significant portion of a plant’s stored energy.
Growing Multiple Sets of Leaves
Here in Colorado late spring freezes often zap those first sets of leaves. At that point, the plant has to dig deeper into its reserves to come up with enough energy to produce another set of leaves. Some plants will have plenty of energy to pull this off, but some won’t. Those that don’t may produce fewer leaves and may be weak for the season or even years. They become more susceptible to disease and less drought tolerant. What’s worse is when an even later spring freeze zaps the second set of leaves! And yes, this does happen! This is when you will see many more plants struggle or die.
A spring with late freezes is exactly what we don’t want after a fall like we just had when many plants weren’t able to transfer energy from leaves to branches or roots to store for the winter. Plants whose leaves froze before chlorophyll broke down in fall will be less likely to have the energy to produce multiple sets of leaves come spring.
The Importance of Staying Dormant
So why do some types of plants handle our unpredictable springs better than others? A major factor is that some plants aren’t fooled out of dormancy prematurely. Plants that come out of dormancy easily don’t tend to survive in Colorado as well as plants that require a longer stretch of warm weather to be coaxed out of dormancy. In Colorado we can have two or even three weeks in a row of warm days in the middle of Winter. As much as I am sick of winter by February, I dread those long stretches of warm winter days. I know I have some plants that will get fooled and start coming out of dormancy. I also know that we still have plenty of freezes right around the corner.
Failed Attempts
One of the most beautiful evergreen shrubs I ever bought was a stunning Dwarf Hinoki Falsecypress. I had admired these gorgeous shrubs many times in gardening magazines, but I had never seen one in my area. While it seduced me at the store, a voice in the back of my head kept reasoning with me that, as beautiful as they are, there must be a reason why I never see them around town. But the tag said it was hardy to zone 5, and even though I knew that I shouldn’t buy it, it was so beautiful I couldn’t resist.
It thrived over the summer and seemed to go into dormancy just fine. It was still a deep green and as beautiful as ever near the end of February. I started to think that maybe, just maybe, it would live out a long, happy life in my garden. But we had a warm spell for a couple of weeks starting around the end of February. Then suddenly, winter was back. Almost as suddenly, my lovely, lush, green false cypress turned brown and brittle. Like many other plants in my yard, it came out of dormancy during the warm spell. However, unlike the others, instead of just the new growth dying once the freezing weather returned, the plant died.
The following year, I tried another Hinoki Falsecypress, and the exact same thing happened after another winter warm spell. Both were planted in the same spot – a spot that warms up quickly in spring – which I now realize was a mistake. Since then I have identified some ways to help plants survive Colorado’s complicated winters.
Mulch is Key!
So, what can we do to try to help our plants survive our late freezes in spring or warm stretches in February and March? One of the best ways to help your plants survive Colorado winters is to prevent them from being fooled into thinking that spring has arrived when it is really just a warm spell in winter.
Think of the “brains” of plants as being in their roots. If the roots still believe it is winter, the plant won’t come out of dormancy. To help prevent the roots from being fooled, be sure to place mulch over them in the fall. Two to three inches of mulch will keep the soil and roots at a more consistent temperature and won’t allow the soil to warm up as quickly. This reduces the likelihood that your plants will think spring has sprung during one of our winter warm stretches. I would strongly recommend mulching before spring this year. Many plants may be low on stored energy due to leaves freezing last fall before the chlorophyll broke down.
Find Your Garden’s Coldest Micro-Climates
Another way to help plants that are tricked out of dormancy easily is to plant them in micro-climates within your garden that stay colder (and probably get less sun) during spring. You might notice that your gardens on the north side of your house seem like they are a week or two behind your gardens on the south side when you compare their growth in spring. This is because the soil on the south side warms up much earlier in the warm sunshine of spring than the soil still falling within the shadows on the north side.
One of my favorite areas of my garden is along the north side of my house. The area is cool, shady and lush, and the plants that grow there, such as my beloved Dwarf Serbian Spruce, give it a very woodsy feel. It stays in the shadow of our house well into May. Consequently, this area is the last area in my garden to come to life in the spring. I originally had some daffodils planted in the area, but the rest of my garden was already in full spring swing before they ever opened. I moved them to a sunnier spot where I could appreciate their cheery flowers when little else was in bloom. Plants in the area along the north side of my house come out of dormancy weeks after the plants on the south, and they are never tricked out of dormancy.
It is important to identify the different micro-climates within your yard. A plant that may suffer in one spot in your yard may thrive when moved over just 5 feet. If a late spring freeze comes along, the plants on the north side of your house and other areas that stay cold for longer will have an advantage because they are less likely to start growing leaves that will get killed by the late frost.
Winter Water
Finally, one more thing that is really important to help your plants survive Colorado’s winters, whether they are likely to come out of dormancy early or not, is to winter water. Water your gardens and trees well once a month during winter unless we happen to get an unusually wet month. Although we do get the occasional good load of snow, over all our winters can be very dry, and dry soil in freezing weather can kill roots. Keeping your garden from drying out over the winter is critical to help your plants survive Colorado’s Winters.
Give it a Shot and Hope for the Best
As a plant addict myself, I understand being unable to resist an enticing nursery plant that is calling your name. Even when it’s a non-native plant that isn’t normally seen in your area and you know its risky. Just remember that one of the leading reasons why that plant may struggle to survive winter here in Colorado is simply that our weather can trick it out of dormancy too easily. So go ahead if you must, and give in and buy the plant! But help it survive Colorado’s winters by planting it in an area of your yard where the soil is slow to warm up in spring, mulch it really well every fall, and water it well once a month throughout the winter. And if you have any luck growing a Hinoki Falsecypress, please let me know! It may be time I give one another shot!!