GardenBanter.co.uk - Live oak treatment in December

On 16 Dec 2006 10:25:04 -0800, wrote:

Hi,

I have several live oaks in my yard (Austin, TX) and
an arborist recommended deep root fertilization plus
a micro injection. He visited my property November 1st
but I didn't schedule an appointment immediately. It
is now December 16. QUESTION: Is it too late now for
the treatment? Should I wait for early spring?

Thanks!

I don't want to get into a battle with another arborist about the
recommendations for your trees, especially having never seen them. I
will make some general statements about fertilization, instead.

First, I like to think of fert. as feeding the soil, not the roots or
the plant. A good balance of nutrients, organic matter, and microbial
life will lead to an active soil ecosystem. In turn, the nutrients
become more accessible to absorbing roots.

If there is not already an excess of salts, the timing should not
matter much (caveat: during extremely hot and/or dry weather,
nitrogen can burn plant tissue, but, even then, accompanying the
treatment with a good soaking should alleviate the problem). I
suggest a soil test before adding any nutrients. Most Austin soil has
plenty (or too much) P and K but not much N and not much organic
matter. Catering the fert. mix to the existing situation will
minimize the chance of damaging the plants and reduce runoff into the
storm sewers and creeks.

As for trees and other plants, too much fertilizer can be a bad thing.
Even if you don't get an overabundance of salts, a weak tree may be
forced into spending its last energy reserves to create the flush of
new growth that will come from a bunch of nitrogen, then it will need
to spend some energy to support that growth. It could fizzle and die
rather than booming forth with renewed vigor. It's not common, I
suspect, but worth noting.

Now, that deep root thing. When we talk about tree roots, we have to
start by understanding how trees look underground. There is not a
reverse-lollipop of a root ball like some people assume. Roots will
exploit any source of air, water, and/or support they can find, but
ideally they form a wide, spreading mat of feeder roots in the top
foot or two of soil that reaches well beyond the tree's dripline.
Meanwhile, some really deep roots are established to help anchor the
tree. Most of the absorption of nutrients takes place in the feeder
roots. Thus, "deep root feeding" really just needs to be deep enough
to get below the grass on the surface. A really deep injection will
put most of the fetilizer below the roots that could use it. I'm not
saying there are no good reasons for deep-root injection, but I think
it is possible to care for most trees effectively without it.

And the injections: Each injection will create a small hole that
penetrates the tree's "skin" and might allow decay or disease to enter
the cambium underneath. These wounds do not heal; the tree just has a
system to minimize the spread of the decay (part pysical, part
chemical). If you come back in a year to do the same thing, you will
need new holes because the old ones will have been plugged up.
Injections have their place, but I would make sure this tree needs
such treatment before going ahead.

My opinion: top dressing the soil with composted manure twice a year
will take care of most Austinites' fert. needs. It will reach the
grass first, it's true, but as it decays it will leach into the soil,
relieving compaction and allowing deeper penetration over time, while
also burning through some of the bonds between calcium and the other
nutrients that are often present but unusable by the plant. As
compost is mostly nitrogen and organics, it suits the soil we see here
most of the time. It is somewhat acidic, which addresses the
abundance of limestone we have. And it is easy to apply, so you can
hire a teenager or a yard man cheaply to do the job.

Meanwhile, a 2-3" layer of mulch over th critical root zone will make
a big difference to most trees.
http://www.treesaregood.com/treecare/mulching.aspx

Again, that's my general opinion on the matter. I am not making
specific recommendations for your trees. But I concur with the
suggestion of a second arborist's opinion. Don Gardner (512.263.2586)
has decades of experience in Austin and does consultations only, so
you needn't fear he is motivated to sell with his recommendations. In
the interest of full disclosure, I know he will usually advocate for
the approach I have suggested, but he will be able to spot situations
that may call for a more intensive approach. If you want, a third
opinion (or a different second) can be obtained easily by looking in
the YP under "arborists" (the "tree work" section is densely populated
with companies along the full spectrum from hacker to expert, so it
can be more challenging to sort out who knows what). Also, the ISA
maintains a site where you can search for local certified arborists:
http://www.isa-arbor.com/findArborist/findarborist.aspx Along with
ISA certification, consultants may be members of the American Society
of Consulting Arborists, which has more intensive educational
requirements for membership than ISA.

To further aid your search for good advice, educate yourself first at
www.treesaregood.com and learn to spot the straight dope among the BS.
Specifically,
http://www.treesaregood.com/treecare/mature_care.aspx talks about
fertilization.

good luck,

Keith Babberney
ISA Certified Arborist #TX-0236AT