Feeding plants is a good practice in ornamental gardening. Using mineral and organic fertilizers you can get excellent results, the main thing is to know how to do it correctly.
The best fertilizer for Blue Spruce is a slow-release universal fertilizer. Use it once a year in early spring and it will be enough for the whole growing season.
For more information on spruce nutrition, read this article. Also, be sure to check out the Colorado Blue Spruce Maintenance Guide.
When to fertilize?
The best time to fertilize Blue Spruce is the first half of spring. Choose a time when it is already awake from hibernation but has not yet begun to grow.
If you use slow-release pellets, one application is enough since most of such fertilizers are designed to last for 90 days. As a result, your spruce will be supplied with minerals for most of the summer.
Applying in late spring may not have the expected effect. This is because the pellets will not start working until the young shoots emerge from the buds.
Avoid fertilizing in the summer or fall as this can lead to active growth. As a result, new branches will not mature in time for frost and will die. The recovery process can take a long time.
How to fertilize?
Before you apply the fertilizer, make sure it contains the three basic elements:
The ratio of these elements in the fertilizer can be equal. For example, a product with the formula 10-10-10 is appropriate. A slight deviation from this is also possible. What you should avoid is using fertilizers with high nitrogen content.
It is also an advantage if the fertilizer contains small amounts of magnesium, zinc, and iron. All of these elements are needed for photosynthesis.
As I mentioned before, the best form of fertilizer is slow-release pellets. The longer they last, the better.
Step 1 to 2 feet away from the trunk of the Blue Spruce and dig a small hole 2 inches deep. Sprinkle a few ounces of fertilizer in there and cover the top with soil. This is to keep the water from washing the pellets away.
To know the exact amount of fertilizer the Blue Spruce needs, be sure to read the directions on the label. Usually, 3-5 ounces is enough for young spruce trees.
Another type of fertilizer that you should use is compost. Quality nutritious compost can provide the Blue Spruce with energy for a long period of time.
The first time you should apply compost is when planting. Pour half a bag of compost into the planting hole and mix it with the native soil. Then plant the spruce in it. This amount of organic matter will be enough for several years.
You should also mulch the Blue Spruce with compost. The nutrients will slowly penetrate the soil and nourish it.
The layer of compost should be 2-3 inches. Avoid covering the trunk with compost to avoid trunk rot. Mulch the entire drip line of the spruce. Renew the mulch once every 1-2 years.
Make sure to use compost from a reputable supplier. It should be free of pests and diseases.
What you want to avoid is the overuse of fertilizer. Once or twice a year is enough for Blue Spruce.
If you fertilize too often, the spruce can grow very vigorously and become very exhausted. The young shoots will not mature as much as they should and will be more susceptible to disease.
After some time of intensive fertilizing a high concentration of trace elements will accumulate in the soil. As a result, the root system can suffer, and the outward sign of this will be a discoloration of the needles.
If you have overfertilized your spruce, water it with a few gallons of water to flush the fertilizer deeper into the ground. If possible, remove the fertilizer from the soil with your hands.
Not enough nutrients
In general, Blue Spruce does not need a lot of nutrients. If the soil is even slightly nutritious, it can do with a minimal amount of fertilizer. But there are still situations where fertilizer is a must.
First of all, this applies to poor soils, such as sandy or stony soils. In such soil, the spruce will develop slowly and may not have a rich blue color. To remedy this, fertilize it as described above.
The second case is when the soil is too alkaline. In such a soil, the plant is not able to assimilate nitrogen and some other minerals. As a result, the needles can turn yellow.
To fix this you need to lower the pH. Use aluminum sulfate or garden sulfur. Also, mulch the spruce with peat and mix the topsoil with peat. All of this will make the soil more suitable for growing Blue Spruce.