...and fertilizer too? But maybe, probably not!
First, the problem:
In a class, you mentioned we do not need to deep root feed
our evergreens because of all the needles that fall from the
evergreens and that provides enough of the acid it needs. I'm
asking this because I need to have my Colorado Spruce evergreens
sprayed because of Gull or whatever it is that is on them. I just
got the price quote and it included deep root feeding of all the
evergreens. I have 6 of them in the back area of the yard sitting
in black gold so those I don't understand why they would need deep
root feeding. One of the Colorado Spruces along the side of our
home has always struggled so I'm wondering if it would benefit from
it or not. Just don't have the extra money laying around now but if
I need to do it I will. I just don't trust salesmen/retailers as
they are there to sell product.
Several angles to examine, each requiring explanation:
1) You may not need to treat the spruce gall with insecticide or
anything else. If you do, be aware that timing is critical.
2) You may not have to
fertilize at all. If you do, surface application is best.
3) Evergreen needles don't
acidify your soil.
4) Improve a tree's health, it'll manage its own pests.
5) One way to improve a tree's health: Aerate
You may not need to treat spruce gall, at all!
If your trees are hosting the most
common gall-making insect that affects spruces -- an
insect called Cooley spruce gall adelgid -- their problem
is cosmetic. That is, it may look unattractive but it is
not life threatening. If your trees are hosting spruce twig gall
makers they may need help if they're very young or the infestation
is very heavy.
Cooley spruce gall adelgids infest the growing tip of a spruce
limb and feed by sucking on the needles. Their excretions cause the
tip's growth to become distorted, and the tip
dies. Nevertheless, the loss of even a hundred tips is
not a serious blow to a good sized, vigorously
twig gall affects the wood of the branch, causing it
to deform and weaken. The tree may later shed that branch. Because
whole twigs are lost, the overall loss to the plant may be greater.
A tree might need help getting ahead of twig gall
even though its total insect load is smaller than one with Cooley
adelgids which we leave to its own devices.
gauge the damage
The general rule is that if less than 20% of a plant's
foliage is being lost to a problem, it's not a
significant issue. Young trees might be harmed at lower
rates then older trees.
It's important to determine how much damage a tree's
sustaining. 20% foliage loss is a break point between "let it go"
and "consider intervention." Here there are about 10 dead tips, but
at least 28 undamaged tips plus many unaffected segments of equal
size/needle count behind the tips on each branch. With 10 tip
segments lost from at least 160 healthy segments, it's 6% damage --
no big deal.
This is that 6% damaged tree. Our eye may focus
on the brown but the tree isn't in danger.
Fertilizers: Best used when
prescribed by soil test
Second, you do not need to fertilize trees and shrubs if their
growth rate and color are normal for their species and/or if a soil
test indicates all nutrient levels are normal.
A given fertilizer may contain one or a number of chemicals --
plant nutrients -- that are necessary to good plant health. Many
fertilizers supply the three chemicals plants use in greatest
quantity, namely nitrogen, phosphorus and potassium -- N, P and K.
Without a soil test we can only guess which
fertilizer -- which mix of nutrients -- should be
Dark, rich soil can have
nutrient deficits, especially if raked
We are safe to guess that a very dark soil has adequate
nitrogen. It's the presence of humus that makes it dark --
humus, which is a material that remains after organic matter
decomposes. Since nutrients are released as organic matter
decomposes, we call a soil that contains 3% organic matter "good."
A black soil may have over 5% organic matter. Each percent of
organic matter in the soil translates to about one pound of
nitrogen released to the soil each year. Since the average
plant requires nitrogen at the rate of two pounds per 1,000 square
feet per year, dark soil may not need extra nitrogen.
However, darkness is not an indicator of other
nutrients' presence or absence. A dark soil may have
enough or too little potassium, phosphorus or micronutrients --
elements that are also essential but are dubbed "micro" because
they are used in less quantity than the big three.
Some gardens operate at a loss because we prune and weed and
rake, removing all or most of the organic matter that could or
should fall on the soil. That can deplete even the best soil.
That's why it's good to use slow
release organic fertilizer for both nutrients and to supplement
organic matter, and test the soil from time to time to know if and
which fertilizer may be necessary.
Fertilizer best spread on
When fertilizer is needed, it's best to deliver it to
the entire root zone. Most nutrient absorption happens in
fine roots very near the soil surface, so broadcasting fertilizer
over loose soil is ideal. Placing it deep, in
concentrated doses is not necessary and can be a
waste. Yet sometimes the action of placing it
deep may help in ways unrelated to the nutrients. (See Aeration.)
Third, there's no acid reaction
from evergreen needles
It's a fallacy, despite being long-held and
often published: The notion that needles and other evergreen
foliage acidify soil has been overturned during the advance of
composting science. Needles may influence the surrounding soil's
relative acidity (pH) as they rot, to make a soil temporarily acid.
Then it is quite normal for the pH to swing the other way,
stabilizing at slightly alkaline. However, the same changes happen
during the rotting of almost any type of organic matter.
If you need proof, do two separate soil tests
in your yard, taking one sample from an open-sky bed and one of
soil from under a mature pine, spruce, yew or juniper. You will
probably see no significant difference in pH. We have done this.
Each time, all of the beds tested nearly the same, within normal
range for our region (mildly- to very alkaline). In one case a bed
under 50 year old pines was the most alkaline area on the
We don't know where evergreen foliage and soil acidity became
garbled. When we see poor growth under evergreens we often find
that water is an issue. Even when watered as well as other areas,
plants there may fail to thrive because the dense foliage so
effectively blocks rain and snow.
give them what's right and let 'em grow!
Fourth, plants normally take good care of themselves if we
simply give them proper growing conditions. If a plant struggles
because it doesn't have the light, water, or soil type suitable to
its species, insects or diseases which would otherwise be
non-issues can become big trouble. Sometimes one struggling plant
in a group may even contribute to healthy plants' problems by
allowing insects or fungal spores to multiply. If a tree is growing
poorly, figure out why. Fix that issue and other problems will
Wonder working: Soil
Last but probably most important, aeration is one of the best
things for struggling plants in landscape situations. Densely
packed soil is common around buildings. It has too little oxygen
and conducts water too poorly to keep roots healthy. Trees there
don't establish adequate, wide root systems. When the roots are
inadequate the tree may be unstable as well as unable to fend
off its pests.
One way to break up compaction is to drill holes at regular
intervals all through the root zone (see Spruce Down
to envision the root zone). Fill the holes with looser material
or compressed air. That encourages everything from worms to
beneficial bacteria and fungi. The soil animals and/or air crumbles
the sides of the hole. The effect gradually spreads.
Sometimes what is called deep root fertilizing involves drilling
holes, inserting fertilizer and blowing in compressed air. The
action of applying fertilizer in that way aerates the soil. Side by
side tests have been done to compare trees fertilized that way to
trees treated that way sans fertilizer. Trees responded
as if fertilized from aeration alone.
Be confident of who will work with you
To summarize, don't treat the trees unless you know which gall
you're dealing with, how much foliage is being lost, whether
aeration is involved, and what basis was used to prescribe and
choose the fertilizer. If the company that gave you the proposal
can tell you all this, connecting each item clearly to the actions
they've prescribed, that's someone you want to work with. If they
cannot enumerate or explain, ask someone else to look at your trees
and make a recommendation.
Each Cooley spruce adelgid gall is the plant's own branch tip,
grown thickened and twisted, and now dead because of the insects'
secretions and feeding. A heavy infestation might be controlled
with a well timed insecticide application at budbreak sprayed
forcefully so it penetrates the dense growing tips. Any action
during other seasons is not warranted, other than to clip off the
unsightly brown. Why? An arrow points to the exit holes. The
adelgids are gone until spring.
The mature adelgids overwinter on the spruce twigs, near the
buds where their young will take upresidence. When the cornelian
cherry (Cornus mas) is in full bloom, or a serviceberry's
(Amelanchier) flower buds are just showing, or red maples
(Acer rubrum) are in full to late bloom, those adults are
about to lay eggs. This is before the spruce breaks bud.
At that time and almost no other, the insects are vulnerable to
If your tree care company operates by the paper calendar rather
than by local plant development, they're likely to miss this
window. Make yourself a note to watch a neighborhood cornelain
cherry, serviceberry or red maple and call your tree care proivder
to say, "Today you need to be here."
Below: Take a page from Don Orton's well-respected
reference, Coincide and learn enough about
a pest such as Cooley spruce gall adelgid to test your tree care
service on their knowledge.