Spring is the best time to fertilize your apple trees, as soon as the snow is gone and any flowing groundwater has drained off. Trees should be fertilized before the buds swell. In Northern Ontario, this is usually late April to early May.
Not sure how much fertilizer to apply to your apple trees? The typical formula is this:
1/10 of a pound of nitrogen for every inch of trunk diameter two feet up from the ground
or
1/10 of a pound of nitrogen for every year of tree age
~to a maximum of 1 pound of nitrogen per tree~
Many folks use 40 lb. (18 kg) bags of manure that are labelled 1-1-1. This means the manure is 1% Nitrogen, 1% Phosphorus and 1% Potassium. Manure is an excellent fertilizer for apple trees because it tends to be balanced. Although the tree is really looking for nitrogen in the spring to get itself going, applying nitrogen alone without other nutrients (potassium in particular) can lead to problems later. Here’s how you would calculate how much 1-1-1 manure to apply:
Example: young apple tree with a trunk diameter of 6 inches:
Diameter: 6 inches
We need 1/10 of a pound of nitrogen per inch of diameter
So, 6 x 1/10 of a pound = 6/10 of a pound, or .6 of a pound
.6 divided by .01 (the 1% indicated on the bag) = 60
So, that is 60 lbs. of manure (1 and 1/2 bags)
Example: mature apple tree over 10 years old, or with diameter over 10 inches:
Diameter: 10 inches
We need 1/10 of a pound of nitrogen per inch of diameter
So, 10 x 1/10 of a pound = 10/10 of a pound, or 1 pound
1 divided by .01 (the 1% indicated on the bag) = 100
So, that is 100 lbs. of manure (2 and 1/2 bags)
Apply the manure to an area extending a bit outside the dripline of the tree. Avoid applying it right against the trunk.
If you decide to use more concentrated fertilizer granules, just use the above formula to determine how much you need. I usually use a mix of manure plus a more concentrated organic fertilizer such as the Fafard products you can get from Belluz Farms.
Fertilizing Later in the Season
If you determine that the tree needs more fertilizer later in the season, remember that July 10 is the cut-off. Applying fertilizer beyond this date will hinder (and I mean seriously!) the tree’s ability to prepare for winter by ceasing growth and hardening its outer surface.
Happy fertilizing!
