Weather Damage To Plants

I have been speculating since last October that we could see weather related plant damage this spring, and we are far enough into May to begin to see the results of that early October freeze. October 8th last year temperatures were in the 70s and October 9th and 10th they dropped to low 30s. Many plants cannot recover from that kind of temperature change. Specifically, many of the linden’s leaves were frozen before they had their fall color change. The tender new growth of many plants had not hardened off and was injured at that time. Weigela are one of the plants that we see injured this year. So add to that our dry, mild but windy winter that allowed plants to dry out and you get to March 2020 with high temperatures in the low 60s and low temperatures down to 13 with very little precipitation. If that was not bad enough, we get to April and temperatures were on a roller-coaster ride of high temperatures in the low 60s to a low of 20 and more than one night in the low teens. Many plants that started to bud in those warm days were killed by the cold nights. It is hard to say if newly planted plants, i.e. plants planted within the last year, took the weather harder than established plants. These weather swings are part of gardening in Montana and happen every few years. To add insult to injury, many areas around the valley got pounded with hail, some more than once. We had a similar October freeze event more than a decade ago in the Bitterroot that was particularly hard on birch, maples, roses and even barberries not to mention random perennials. I know it is hard to put a positive spin on losing a plant in your yard.

In my experience, there are a couple of things you can do to try to reduce the potential of this kind of injury. Again, much of the plant material that gets damaged in an early freeze has not had a chance to mature enough to survive the cold. A couple of reasons for late new growth on plants can be fertilizing too late in the season and not reducing your watering in the fall to help signal the plants to prepare for dormancy. Talking about fertilizing trees and shrubs is a separate issue from fertilizing your vegetable plants or lawn. Vegetable and annual plants have a very short time to do a very heavy job and need a good bit of fertilizer to make that happen and when it frosts, they are done. Trees and shrubs need to follow their internal season for growth and weather, and if you fertilize too late you will push fresh growth that can freeze and then you have probably done more harm than good. Another problem of pushing too much new growth is that aphids love fresh leaves so there is no point in attracting them. Trees and shrubs prepare for dormancy with the changes in the amount of light each day, changes in temperatures that are more normal than roller-coaster, and changes in the amount of late summer water. To cut to the chase, fertilize trees before July 1 or wait until they drop leaves in the fall. For established trees start reducing the irrigation in September as the days get shorter and temperatures begin to cool. Newly planted trees need to be kept evenly moist to encourage root growth to get them ready for the winter, so you need to pay attention. Once a tree has lost its leaves you can water again until the ground freezes even if that means watering after your sprinkler system is turned off. When you do fertilize trees please use a fertilizer with a low nitrogen number and be sure to water it in well. I am not a fan of fertilizer spikes as I am too lazy to pound them into the rocks in my yard and they do not work very well if they don’t get wet. I like Milorganite fertilizer because you can use it on everything, and you can’t screw it up. It is a slow release nitrogen and phosphorus with iron that works slower than synthetic fertilizers and helps to better feed roots and improve soil structure. Side note, Milorganite does have a bit of a smell that dissipates quickly. Deer usually don’t care for the smell, but your dog might want to roll in or eat it. It’s a win if it repels deer and it won’t hurt the dog.

I have already talked about aphids as a heads up for scouting in your yard. Well, the aphids are out in full force right now. Last week I tag teamed with a friend from the nursery business here in Billings to give a talk on scouting for pests. My friend reminded the group that most aphids have a specific host so the aphids on your plum tree are unlikely to get on your roses. Remember to decide your acceptable threshold of pests when deciding to treat. Older established plants are generally not harmed by aphids but they can cause younger trees to struggle if the infestation is heavy.

We have had customers ask about oak and birch trees that seem to be slow to leaf out. Even with the crazy weather oaks and birch are slow to leaf out in the spring. Birch generally start to leaf at the lower branches and then it works up the tree to the top. If you are concerned about your birch or other trees, scratch the bark with your fingernail to see what color it is under the bark. If it is green, the tree is still trying to grow. If it is brown that area is not alive. If the branches are still flexible and have buds they are still growing. If the branch snaps right off that area is not alive. Folks ask me why only one of 3 or 4 plants of the same kind in a row died? That is a plant detective question that leads to numerous other questions. 80-90% of all plant disorders are brought on by environmental conditions. Could it be that not each of the plants in the same row get the same amount of sunlight so the soil warms up at the same time? Are they all protected the same from the wind? Or is the dead one on the path of the deer in your neighborhood? Is it the dog’s favorite place in the yard? Or did you accidentally get too close with the weed spray? Is it the right plant for that location? The more items we can rule out the closer we can come to a diagnosis. Keep in mind that sometimes there is not a clear answer.

Here at the nursery we are still getting in shipments of plants. We are expecting water plants, more perennials, and more shrubs including hydrangea. This has been a strange year in the nursery business and we are finding some gaps in the supply chain, not as glaring as toilet paper, but our suppliers are still rolling as fast as plants are ready to ship. If you asked us to look for plants, please follow up to see if we were able to find your plant. We have been able to get more fruit trees, a few more raspberries as well as starter perennials, and a restock of shrubs and ornamental grass. We still have tomato, pepper and squash transplants. This is still a great time to plant to get trees and shrubs rooting in before we get to the expected summer heat. I notice that some perennial shoppers buy when the plants are in bloom, but the best time to plant perennials is before they bloom so you don’t damage the blooms as you plant.

Please stop out to wander around, get ideas or check our stock.