Black Hills Spruce
Colorado Blue Spruce
Black Hills Spruce
Colorado Blue Spruce
About Fertilizer And Fertilizing Evergreen Trees
If you have little or no experience with fertilizer, DO NOT fertilize your newly transplanted evergreen trees for one full year! Or, you are likely to kill your trees. Timing, formula, and application should be clearly understood before fertilizing anything.
In good soil, your evergreen tree's best friend is WATER. The best and only thing you can provide your newly transplanted evergreen tree is WATER.
Water your evergreen tree moderately, but make sure you do not soak or drown the tree.
Like all landscape plants, evergreens remove nutrients from the soil. In the forest, needles and twigs accumulate on the ground and return nutrients to the soil (natural fertilizer). Under cultivation, evergreens usually receive fewer nutrients from this source because some needle and twig litter is removed beyond the drip line or tips of their branches.
You should allow your evergreen tree needles to accumulate beneath the tree and past the drip line to help replenish nutrients for the tree.
At some point it might be necessary to fertilize your evergreens, though evergreens generally require less fertilizing than deciduous trees. In many landscapes, evergreens also benefit from fertilizer applications to the lawn.
In many cases, evergreen trees may never need fertilizing.
The plant itself will often indicate when, or if, it needs fertilizer. If growth rate and needle color are normal for a particular variety, fertilization is not necessary. If new growth is sparse or slow, or the needles are not a healthy color, or are shorter than normal, you should probably fertilize. Keep in mind, however, it is not unusual or abnormal for newly transplanted evergreens to exhibit slow growth, yellowed needles, or needle loss until they are re-established, usually in the spring.
Newly transplanted evergreen trees should not be fertilized for one full year.
Regular fertilization may be recommended if you are trying to grow evergreens in a less than ideal site, such as very sandy or heavy clay soil, or if the plant has suffered damage from insects or disease. You might also wish to fertilize to encourage more rapid growth in relatively young evergreens.
If you do fertilize your evergreen trees, do not fertilize the trunk area and especially not the trunk itself. Fertilize your evergreen trees between a foot before and after the tree drip line.
What to Use?
A complete fertilizer that supplies nitrogen, phosphorus, and potassium, such as 10-8-6, is often suggested for an already established tree. This formula can vary somewhat, but usually the nitrogen content (the first number) will be higher than the phosphorus (second number) or potassium (final number).
Knowing the best way to apply fertilizer to your evergreen trees requires some basic knowledge about the product you are using. Fertilizers, whether organic or chemical, are always labeled with three numbers. For example, a bag of fertilizer may have the numbers 12-12-12 or 28-8-3 or 0-0-64 on the label. These numbers hold the key to proper fertilization selection.
The numbers stand for N-P-K. The “N” refers to Nitrogen. “P” is Phosphorous. “K” is Potassium. Each is listed on fertilizer labels because each plays an important role in the development of the tree.
- Nitrogen is the first of the three numbers on the label, and it is the nutrient needed to make the tree a dark, lush green color.
- Phosphorous is the second number, and it helps the growth of strong, deep roots.
- Potassium is the third number, and it gives the tree structure endurance for extreme weather conditions.
The numbers represent the percentage of chemical weight to inert matter. For example, if you have a 10 pound bag of 20-10-10 fertilizer, then two pounds of the product is Nitrogen, one pound is Phosphorous, and one pound is Potassium.
Once the numbers make sense, then it is necessary to find the right product for the project. If you are looking for a basic fertilizer that serves all the functions, a 12-12-12 mix is good. If you are seeking a dark green look, then a higher first number with lower second and third numbers is the choice. For a newly planted tree, the middle number should be higher to help the root development.
It is always best to have a reliable soil test run before fertilizing, as much of our soil already has sufficient amounts of phosphorus and needs no extra. Testing will also show whether the soil is acidic or alkaline. Generally, evergreens grow better when soil conditions are acidic; many nutrients may be unavailable to the plant when soil is too alkaline.
Timing Fertilizer Application
The best time to fertilize is early April, before new growth expands, but you can apply fertilizer anytime until midsummer (roughly July 15). Applications beyond this period will stimulate growth late enough in the season that it may not have time to harden off before cold temperatures arrive. Such growth is much more likely to suffer winter injury and dieback.
An exception would be the use of slow or timed-release fertilizer such as Osmocote or Sta-Green. A light application in late summer or early fall may help nutrient-stressed trees come through winter in better shape. Mid to late autumn applications of slow-release fertilizer are also usually safe.
NEVER, DO NOT fertilize drought-stressed plants. If conditions become quite dry after you've fertilized, it's doubly important to water your evergreens regularly.
Timing is important! Fertilizers with high nitrogen levels, or 1st numbers, are best applied in the cooler parts of the growing season, early-mid spring and mid-late autumn. If you apply these during the heat of the summer, the chemicals will stress out the tree. On the other hand, fertilizers with a high third number are good for late spring and late fall to assist the tree through the weather extremes.
A hand full of Holly Tone can be applied to newly transplanted evergreen trees (at the drip line) after six months to encourage good health and color.
How Much Fertilizer to Use?
Fertilizer recommendations are usually given in pounds per thousand square feet. To find out how much to use, figure out roughly how many square feet your tree or shrub covers. For instance, a spruce that measures five feet across would cover twenty-five square feet. If it were large, with branches extending five feet in each direction, it would be ten feet across, and cover about one hundred square feet, in total.
A common "maintenance rate" of fertilizer is two to four pounds actual nitrogen per thousand square feet of soil surface, applied every two to four years. For mature, slower growing trees, one pound of actual nitrogen is probably enough.
Figuring Actual Nitrogen
It's easy to figure out how much actual nitrogen is in a bag of fertilizer, because the numbers in the fertilizer analysis are actual percents, by weight.
A forty pound bag of 10-8-6 is ten percent nitrogen. Ten percent of forty is four, which means the entire bag contains four actual pounds of nitrogen (plus phosphorus, potassium, and an inert carrier). A thirty pound bag of 21-0-0 is 21 percent nitrogen. Twenty-one percent of thirty is 6.3, which means the bag contains 6.3 pounds of actual nitrogen. (The rest is an inert carrier.)
The final consideration is the type of product and applicator to use. As a general rule of thumb, fertilizers are most effective in granular form. The granules fall to the surface and connect with the soil where the proper chemical reaction can take place. The use of liquid fertilizer on a small scale is virtually worthless. It does not produce the same desired effect because the chemicals do not carry as high of a weight concentration. It takes a much greater volume of liquid fertilizer to gain the same effect as granular fertilizer.
In the same vein, using “weed and feed” products for post-emergent weed control is also not the most effective method. The product you are applying needs to both reach the soil to provide the nutrients, and stick to the leaves of the weeds to kill them. It is impossible to get 100% coverage in both of these areas at the same time with one product. Instead, fertilize the tree first with a basic granular fertilizer, and then spray the area or around the tree with a post-emergent weed control.
The applicator can be a broadcast spreader or a drop spreader, both are equally effective. It is very important, however, to have a product that has a spreader setting listed on its label that corresponds with your spreader. Many turf fertilizer brands offer both the spreader and the fertilizer products. This eliminates the guess work that can come from having a spreader and fertilizer that come from competing companies. Competing companies do not always list the proper settings for their competitors’ products.
Using Spikes or Root Feeders
Fertilizer spikes are a convenient and simple way to fertilize evergreens, and are effective when used in sufficient quantities. However, since each spike contains only a small amount of fertilizer, they are not cost-effective compared to granular products.
Applying liquid fertilizer through a root feeder is another option on all but heavy, poorly drained soil. But it can also mean additional work when applied to light, sandy soil. Liquid fertilizer leaches through sandy soil quickly, and may need to be applied several times throughout spring and early summer. Again, this method of fertilizing, though convenient, is more costly than applying standard granular fertilizer.
Keep evergreens healthy by mulching the soil surface under their branches and slightly beyond. Start a couple inches out from the trunk, and apply the mulch three or four inches deep. Not only can you apply fertilizer right over the mulch (watering it in well), but mulch will help retain soil moisture and insulate roots from fluctuating temperatures. In the landscape it has the added benefit of protecting plants from grass and weed competition as well as injury from lawnmowers or weed whips.
Typically, evergreens are mulched with wood chips or shredded bark. However, any mulching material will do; well-rotted manure or seasoned compost will add a small amount of nutrients as they break down further. Do not lay plastic sheeting under the mulch. Usually weeds are not a problem, but if you want to put down a barrier, choose a landscape fabric that "breathes" and allows moisture to both enter and leave the soil.
A bit confused?
Go to your local garden center and find their expert in fertilizer, explain what you want to fertilize and when, and let them send you home with the right schedule, formula, and application.