All living things require nourishment. Now is the time to provide food for berries and fruit trees, as well as ornamental trees and shrubs. If you want healthy plants, and trees that will provide shade or bear large, high quality fruit, fertilizing should be a regular part of maintenance
One reason for applying fertilizer now is so melting snow, along with other moisture we can expect, will carry it into the root area. If there is snow on the ground, that's fine. The fertilizer will help melt it, and as it does, the moisture will move the fertilizer to where the plants can use it.As long as we get some rain a week or two after application, there is no problem. Even if there is lawn under the trees, don't worry about fertilizer browning or burning it. It's already brown.
A lawn has a lot of organic material in the thatch that has accumulated. It may absorb some of the fertilizer, so it doesn't get down to tree roots as readily. And as soon as the lawn starts growing, it can take up so much of the fertilizer that it may not be of much benefit to the trees. That is one good reason for getting it on now, while the lawn is still dormant.
Instead of adding more fertilizer to make up for what the lawn may use, punch holes in the lawn area, using an old broom handle, crowbar, or the like, then put the fertilizer in the holes. Punching the holes shouldn't be difficult because of the moisture in the soil, unless the ground is frozen. In that case, wait until it thaws. Even a shovel can be used to cut a slice through the lawn and add the fertilizer.
The holes should be about 10-12 inches deep to get below the lawn roots. The holes should be made under the canopy of the tree limbs. Come out from the trunk about one-third of the way, then make the holes in the other two-thirds of the dripline area. If a tree is getting a good size, it may have killed the lawn under the tree. If so, the holes won't be necessary.
Nitrogen is the fertilizer needed by the trees, whether they are fruit or ornamental. Our soils have a fairly high level of phosphorous and potassium. Perennial plants have the ability to supply their needs since roots are active most of the year. I use ammonium sulfate because it's readily available and relatively inexpensive. Its formula is 21-0-0. You'll use two-thirds as much of ammonium nitrate, 34-0-0 to get the same amount of nitrogen. Whichever is your choice, follow recommended amounts so you don't burn tree roots.
Ammonium sulfate has more of an acidifying affect, which is a benefit on our high pH, alkaline soils. Some gardeners may still prefer using barnyard manure for fertilizer. Manure, if readily available, is a good soil amendment, or conditioner, but as a source of nitrogen, it is uneconomical, and you never know just how much nitrogen the trees are getting.
How much fertilizer should you use? It will depend on the size of the tree. For a fruit tree 2 to 3 years old use 1 1/4 - 2 1/2 cups of ammonium sulfate; a tree 3 to 8 years old, 2 1/2 - 5 cups; mature trees, four pounds (eight cups) large apple or cherry trees, 5 - 7 1/2 pounds. Fertilizer should be applied one month before blooming time in the spring. Fertilizing early allows the nitrogen to move into the root zone along with spring moisture.
The amounts of fertilizer needed for shade trees depends on the diameter of the trunks. The idea with these trees is to encourage enough growth to provide quick shade for your yard. For a tree 2 inches in diameter use 1 to 2 cups of ammonium sulfate scattered around the dripline area; for a tree 2 to 4 inches in diameter, use 2 to 4 pounds of fertilizer, beyond 6 inches in diameter, use 6 to 9 pounds.
Raspberries need about 1 pound of ammonium sulfate per 10 feet of row as the snow is melting. Strawberries should be fertilized little, if any, this time of the year. If you missed the August application, add a complete fertilizer such as 16-16-8 (1/2 cup) or 5-10-10 (1 cup) per 10 feet of row after you clean up last year's dead leaves.
If grape vines had a lot of growth the size of your little finger or larger, skip fertilizing them this year. Their extensive root system is very efficient and added fertilizer usually is not needed.
*Hatch is a horticulturist with the Utah State University Extension Service.