Q. We did a landscape conversion, removed the lawn and
now our tree-sized specimen, multi-trunked photinia, is declining. The trunk has
cracks, it’s gray and looks ugly. We bought Tree Secret fertilizer and applied
water per the directions and it seems to be better. We added more lines around
the basin to increase the amount of water and have mulched around the tree.
When is the right time to trim it?
A. The photos you sent regarding the photinia were eye
opening. I will post them on my blog as well, Xtremehorticulture of the Desert.
These cracks in the trunk and gray color are from intense desert sunlight
shining on the tender trunk. This might also include borer damage under that
grey, cracked area of the trunk. The grey cracked bark is covering the dead
side of the trunk so go ahead and remove the bark and see.
In my
opinion, you would have improved the plant by just applying water to a larger
area under the canopy and not an expensive fertilizer. Applying a quality compost to that area gives the same
benefit as any well-balanced fertilizer. In fact, a well-balanced fertilizer is
formulated to substitute for what a compost does naturally. There are no “secret ingredients” when growing
plants, just marketing and “time savers” similar to “Hamburger Helper” used in
some kitchens.
This
intense sunlight shining on a tender trunk results in sunburn, then death to
the part of trunk that faces this intense sunlight. This damage is oftentimes followed
by attacks by boring insects starting the same year as the damage. Sunburn is
known to attract boring insects which has been the consequence of sunburned plants
over and over for eons. Desert plants like palo verde and mesquite do the same
thing if their tender trunks are exposed like your photinia.
What does photinia look like in a milder climate?
There
are two problems going on. Photinia, native to Japan, is not a desert
plant and its trunk sunburns easily when exposed to intense sunlight. The other
is the landscape microclimate, i.e., where it is planted in the yard.
What to
do? Obviously, this plant can’t be moved to a cooler microclimate in the yard. And
it appears to have done well in that spot before the landscape conversion. I
would expand the area irrigated to as much of the area under its canopy as
possible. Ideally, irrigating the entire area under the canopy is best.
Secondly,
root prune the plant to the edge of its canopy by slicing into the wet soil at
the canopy edge with a sharp shovel. The photinia has this fall, winter and
spring to grow new roots just inside its canopy before it gets hot again. These new roots will find the water.
The direct harsh sunlight caused significant damage to
the exposed trunk. Microclimate. I think exposing the tender trunks to direct
sunlight may have burned them. Not much you can do that looks nice. You could
paint the trunks with a very light coat of paint (light colored latex diluted
half and half with water) but that might look kind of weird considering. If
there are suckers that are growing from that area then leave enough to shade
the trunk until it heals. Plant other plants in that area to shade the trunk.
The trunk will heal in a year or two if this problem
hasn’t already strangled the trunks. You might
consider planting something tolerant of the heat to shade the trunk and give it
a chance to heal. You might consider lightly draping some burlap between the
sun and the trunk to shade it until it can provide its own shade. But whatever
shade you can create to keep the sun from damaging the trunk will help.
Nice!