[VoodooChile]

I was out at a maintenance account this week, and a tree service was there fertilizing some old growth Burr Oaks (Quercus macrocarpa). These are grand old trees, with deep green foliage growing on rich bottom land soil, and to all appearances in peak health, but I can appreciate why the owner of this property would want to do everything they could to preserve them.

Still, a couple of things about the tree service's methods and timing rubbed me the wrong way, and I was wondering what others here would make of their approach.

1) The applicator was spraying water soluble fertilizer underneath the canopy of the trees, which is mostly meadow grasses.

The only method of fertilizing healthy old growth trees I've encountered involved auguring holes at the drip line, and placing time release fertilizer pellets in the holes, usually in late Fall or early Spring, once every three to five years.

As one arborist I work with explained, feeder roots are found out at the drip line of the tree, not beneath the canopy, and the fertilizer needs to penetrate beneath surface vegetation to be utilized by the tree.

2) We are at moderate drought status here, despite 1.5" of rain in the past two days. A general rule of thumb that I've taken as gospel is: Don't fertilize stressed plants. Fertilizer, especially sprayed water soluble fertilizers, induce rapid vegetative growth that a stressed plant struggles to support.

3) Maybe a moot point, but an hour after application, we got drenched with 3/4" of rain in about 1.5 hours, something that anyone who looked at radar in the morning could have foreseen...did any of the fertilizer even get to the tree, or did most of it wind up in the watershed somewhere??? Maybe it's good that it didn't, but given the expense, the timing seems bad...
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Anyway, I don't mean to nitpick, and I've been wrong about best practice many times before (even on this site!), but I have to wonder, rain or no rain:

Can anyone here explain the value of fertilizing healthy hundred year old oaks at the height of summer in the middle of a drought with spray-on fertilizer???

[VoodooChile]

This seems to back me up: Tree and Shrub Fertilization

[jwholden]

Research I have seen indicates that broadcasting granular fertililzer around the base of a tree is as good or better than any other method of fertilizing trees. I've never seen a foliar application of fertilizer for trees, but could be wrong. Perhaps the arborist was spraying some iron or something for Gypsy Moth Caterpillars (bad year for them out here), though you said the trees looked in perfect health.

I often see arborists fertilizing trees with a probe that injects water soluble fertilizer into the root zone. The benefit of this method is more in the aeration of the soil around the roots than the fertilizer applied.

I agree with you on wondering who would apply fertilizer to already stressed trees (or any plant).

[VoodooChile]

I gotta admit that I am surprised more folks round here don't have stronger opinoins about the proper care of the most valuable and irreplacable elements/creatures of the landscape, old growth trees...

A funked patio I can fix, but a dead mature Burr Oak is a legacy lost forever.

[Mark Oomkes]

I don't understand it either. It wouldn't have been one of the national companies, would it? You know the type, they are out as soon as the snow is gone applying pre-emerge when there is still frost in the ground. We usually do the fertilization in the fall (after the first killing frost) with the probe and a water soluble fert w\micronutrients for trees.

I would say that hopefully for the tree it was washed away or diluted, and with that much rain it should have been diluted enough to not do much harm to the watershed. Amazing how those trees made it without any help from anybody and now they need to be fertilized.

[GLAN]

Personaly

I would prefer the longer feeding of granular over the quick fix of water soluble.

Occasionaly we have to go treat a Hemlock Hedge with some feromic and Holy Tone........Other than that......I feel that our lawn fert applications are enough to sustain trees, evergreen and deciduous.

As for shrubs......Our biggest problem is the older plantings that are 30+ years old....usualy are depleated of organic matter in the soil......I have been pushing onto customers spreading compost and or mulch. Shrubs get a fert app in the spring during spring cleanups.

[trees]

You know, it's exactly crap like this that sends mixed (bad) messages to the public. Everyone sees the "experts" out there doing an idiotic thing and take it for gospel. Then those of us that know better have to explain that "we know better". It's a hard spot to be put in.

You see it all over, too. Here in the South, people are convinced that they need to butcher their crapemyrtles every winter, because somehow this practice got established as accepted/acceptable. Or, worse yet, "that huge willow oak is shading out my lawn. I'll get that guy that drove up yesterday to take it down to nubs."

Trees are more than just a single organism. They are home to thousands, reduce energy consumption & are a huge part of the human psyche. It kills me when people don't respect these treasures.

Enough with the soapbox. I'd love to see a stand of old growth bur oaks. What a beautiful tree!

[VoodooChile]

Here's a not great picture (too bright) of the grove in question.

[VoodooChile]

This beauty is the only stressed Burr Oak I've seen on this extensive property. The foliage is mottled brown, perhaps Anthracnose or Bacterial Leaf Spot. I don't think fertilizer will make a difference!

[VoodooChile]

I learned today that the fertilization was done in preparation for 110 yards of mulch that will be spread beneath two groves of Burr Oaks, without removing the pasture grasses growing beneath them.

The justification comes perhaps from Sternberg and Wilson's comment on p. 364 of Native Trees for North American Landscapes that:

Old trees are extremely sensitive to construction disturbance within their root zones and do not appreciate the conversion of a forest duff groundcover to competitve turf.

This entry pertains to Quercus alba (White Oak) but would apply to Burr Oak as well, as it is a member of the White Oak group.

Nevertheless, I think it is important in this case to distinguish between lawn grass (and the fertilizer, herbicide, irrigation and lawn equipment that come with it), and the savanna type grasses that Burr Oak has cohabitated with for eons.

Sternberg and Wilson go on to note of Burr Oak that

This oak...prefers mesic conditions...however it will tolerate environmental extremes. Floods, droughts, limey soils, and even prairie fires can be considered nothing more than a good day's work for this species. (p.378)

Have I mentioned how great these trees look!!! No signs of stress after six months of drought.

If it ain't broke, don't break it fixing it!!!

[jwholden]

In my parts, the good arborists freak every time mulch and tree are said in the same sentence. Too often the mulch is piled too deep and right agaist the bark on the trunk of the tree, a slow and painfull death. How careful do you think somoene is going to be spreading 110 yards of mulch?

[trees]

I bet they spread the stuff with a skid steer, running the machine around, compacting the roots... bad idea!

The spot may be a leaf miner. I've seen a lot of evidence of that on white oak species around here the past few years. Tough little bugger to control, too.

[VoodooChile]

Here's a closeup of the afflicted Burr Oak's leaves.

[VoodooChile]

Under side of the afflicted Burr Oak's leaves.

[VoodooChile]

Not sure if the pest the pencil points to is the culprit.