by Barrie Anderson
As I sit here typing this and glance outside my window, I spot my neighbor fertilizing his Balsam Fir. This typically wouldn’t be an issue in the summer, except it is mid-August now and fertilizing any evergreens at this time, will actually negatively impact them.
Evergreens are a special breed known for their durability, their ability to provide wind breaks, some for their scented needles, and their capacity to provide us with some green during the Minnesota winters. Hence, it’s critical to know when we are helping them and when we are hurting them.
The most appropriate time for fertilizing evergreens is in early spring prior to new growth. This is when they are ready to grow and most likely to absorb the highest amount of nutrients. Fertilizing about 2-3 times a season is the norm for evergreens, however, applying nutrients later on in the season, especially after about mid-July is detrimental. This late boost of nutrients will create new growth that will be young, soft, tender and unable to prepare for the wicked cold our Minnesota winters bring. It also won’t be hardened off enough to protect itself from the typical winter sunscald found on many evergreens during a severe winter.
Ideally, a soil test should be performed before fertilizing evergreens. The reason is evergreens require less fertilizer than deciduous trees, plus they can also be over fertilized, especially young ones… as they are tender, can burn more quickly from too much fertilizer, and this can cause irreversible damage, even death. Being in the softwood category, these guys can absorb faster the necessary minerals required to sustain life. Be mindful though, that too often dosing our evergreens can lead to long, lanky growth as well. This will create a problem in winter, because now that long growth is going to need to stand up to the weight of snow combined with wind, leading to broken branches and an ugly appearance in spring.
For those who fertilize their lawns, that amount put down in the yard may be enough for any evergreens in your landscape! Nitrogen is a component of the chlorophyll molecule, and it promotes shoot growth. Nitrogen is almost always the first number listed on every fertilizer. It is the one macronutrient that is most mobile in soil and can be replenished more frequently, hence, nearly every time you fertilize your lawn, your evergreens are absorbing that fertilizer as well.
Phosphorus is the second required macronutrient for evergreens as it is responsible for cell division, which generates new plant tissue and promotes root growth. Evergreens will need strong and healthy roots to handle the frozen earth created during our Midwest winters.
Potassium is the third nutrient an evergreen will benefit from because this is where they get their heartiness and vigor, if you will. Potassium provides an evergreen’s carbon dioxide uptake, by controlling the pores on the surface of the plants needles, or boughs! As we know, trees, evergreens absorb our carbon dioxide and in turn, provide us with oxygen!
Evergreens need an acidic soil. That means the pH (potential hydrogen, the measurement of the acidity of water) must be less than 7, at the very least. The reason being, the nutrients an evergreen requires aren’t available in a neutral or alkaline soil. Here in the upper Midwest, we have a very alkaline soil and are sometimes challenged to create an environment hospitable for evergreens to thrive. Therefore, careful site selection as well as fertilizer selection must occur in order to maintain your desired evergreen landscape.
As there are several different types of evergreens, they won’t all respond equally to the same fertilizer. Therefore, we must choose wisely. Remember, Nitrogen should be the first macronutrient listed on the fertilizer, as that’s the one mineral which promotes green in any plant, and since we’re focusing on ‘evergreens’, the higher the first number, the better looking the evergreen. A good fertilizer for Pines, Junipers, Spruces, Firs and Yews would be one with a 12-4-8 or 12-6-6. One note of caution, if you have a fertilizer that has a higher amount of Phosphorus (the second number), that will interfere with the mycorrhizae, and they will be unable to perform their job properly. Mycorrhizae are beneficial fungi found living on plant roots. These guys assist the entire evergreen with absorbing the nutrients and water. An overload of Phosphorus will bind to the soil and basically create a traffic jam preventing the other micronutrients, Iron, Manganese and Zinc from reaching their destination.
How to fertilize, you may wonder? Water soluble granules like Mir-Acid is the best method simply because it reaches the plant the quickest. Liquid dosing is absorbed nearly instantly and it’s an easy method of application as well. Always spray the fertilizer at the base of the evergreen so the nutrients can get to the roots expeditiously. The roots are the main highway of travel for all macro and micronutrients, so it’s critical to know where to apply. Foliar sprays are acceptable as well, but only if there is an issue with the soil surrounding your evergreen. One example would be, heavy clay soil. This acts like concrete and really prevents any nutritional uptake by your evergreen, so the next avenue would be to spray the needles, and boughs.
A second method of fertilizing is fertilizer stakes. These are dry, compressed, spike-shaped and capable of being tapped right into the ground at the base of the evergreen. They must be placed at the outer ring of the plant, however, as inserting it too closely to the trunk of the evergreen will burn it for sure. Do not use too many of these either, as they will absolutely cook the roots of your beloved evergreen and you will have a toasted specimen.
Remembering when to fertilize, how much to fertilize, and how to fertilize will give you the tools to assist your evergreens for years to come.