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When you reach the top, keep climbing.
-- Zen Proverb

Fertilizing

How much is too much?

Established trees

Fertilizing is easy to overdo. I now deal with my garden trees like this:

In the fall, after the leaves have turned colour, but before it freezes, everybody gets a dose of granular balanced fertilizer. I try to use ones with nitrogen in the form of urea rather than nitrates. It's slower release.

Each tree gets about a tablespoon per foot of height. This is spread in a band about half a radius wide under the drip line. (Eh? You lost me. If the dripline averages 12 feet from the tree, spread the fertilizer in a 6 foot wide band (half a radius) from about 3 feet inside to 3 feet outside the dripline)

If I miss the fall, then I do it in the spring as soon as I can move through the snow. It's ok to put it on the snow.

In the spring I give everyone about half of this same dose in June. If I can I try to do this one just before a good rain.

Newly Planted trees

During the first year in their new home, I only use a high potassium fertilizer. That's a big middle number. This encourages roots to grow. It will mean that the top half of the tree pretty much sits there, but the tree needs to get it's roots spread out more.

Conifers can be watered with a 50 ppm N solution of 10-50-10 continuously. (ppm = parts per million) Leaf trees can use double that.

1 Kg of 10-50-10 in 1000 litres of water will be 100 ppm. But that's an inconvenient measure. It's 1 gram per liter of water. And a gram of fertilizer is darn close to a quarter teaspoon.

So a teaspoon per gallon is about right for leaf trees. Half that for needle trees. If it's raining lots, cut the water in half, but use the same amount of soluble fertilizer.

Complicating Factors

Fast draining soils need light fertilizer more often. Clay acts as a fertilizer sponge, holding ions on the surface of the microscopic plates. Clay also has particles that are so small that water doesn't move very fast.

A fast draining soil has lots of sand, rock, and chunky bits in it. The organic chunky bits are ok at holding fertilizer, but not great. So basically the tree gets one chance to grab the fertilizer on it's way by.

Because the clay will glom on to the fertilizer, overdoing it is harder on a clay soil than on a sandy soil. So a clay soil might well tolerate a dose of fertilizer at a tablespoon per gallon, without hurting the roots, especially if the soil was dry. On the other hand it might not.

Now you have me confused!

Don't be. It's easy.

First year: 1/2 tsp per gallon of 10-50-10 for needle trees, 1 tsp per gallon for leaf trees until the first of August. That's at 1 gallon of solution per gallon of tree container. If you planted #2 pots, 2 gallons each time.

In the fall: 1 tablespoon of slow release balanced fertilizer per foot of height spread out at around a tablespoon per square foot. (So a 4 foot tree gets 4 tablespoons spread out over a roughly 2 x 2 foot area around the trunk.

In the spring when the tree is in it's growth spurt, about half that.

If you are in doubt, under do it.


Got something to say? Email me: sfinfo@sherwoods-forests.com

Want to talk right now? Talk to me: (8 am to 9 pm only, please) 1-780-848-2548


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Sherwood's Forests is located about 75 km southwest of Edmonton, Alberta. Please refer to the map on our Contact page for directions.