The Washington Post - 29.08.2019

11

DC

the washington post

.

thursday, august

29

,

2019

Gardening columnist Adrian
Higgins answered questions re-
cently in an online chat. Here is
an edited excerpt.

Q: I get the impression that
there are at least two varieties of
crape myrtles in terms of habit:
treelike and bushlike. I was
never told which applied to the
three crape myrtles I planted,
which have now grown tall —
15 feet or more, putting the
display of flowers out of sight
from the house. Is it possible (or
even advisable) to prune them
shorter (after flowering, I would
assume), or should I leave well
enough alone and wish I had
planted the bush-type variety?
A: Crape myrtles vary widely in
habit and application, and it is
extremely important that people
pay attention to the name of the
variety they are buying or having
installed. They vary from four
feet high to nearly 40 feet high
(crape myrtles, not people).
The popular Natchez grows to
30 feet or more. If your cultivar
is too big, you can replace it, try
to move it (if it’s young), or
carefully and conservatively
prune out some branches to give
it a more open look. Don’t simply
cut the tree back — topping, it’s
called — to create stubs or a
hatrack effect. This is commonly
done in late winter and is
appalling. There is a related
practice called pollarding, in
which the tree is cut back to just
above the same point each year,
and in time it produces
“knuckles.” This is done to
lindens and plane trees in
France and England, and I
suppose it is one way of dealing
with the problem. It is much
better to have a clear sense at
planting time of how large a
woody plant will get.

Q: I planted some “Mammoth”
sunflowers in my backyard and
have some blooms about 12 feet
above the ground. The problem
is that many of these blooms are
drooping over. I also noticed that
some of the lower leaves are
showing fungal spots. I have cut
them off but have no idea if this
is to blame for the drooping or if
it‘s just the hot weather. I have
no idea what to do. Water more?
Water less? Remove more leaves?
Any insights would be
appreciated, because we are
close to a month away from
when the seeds are supposed to
be ripe.
A: In general, the larger the
sunflower, the fewer the blooms.
Mammoth is a tall monster, and
like others of its ilk, the flower
head tends to nod down after

pollination. Perhaps this is to

protect the seeds from rain (just

a guess). Feel free to remove the

blighted leaves on your

sunflower.

Q: Unfortunately, I neglected a

very large flower bed, which is

now mostly full of nutsedge, wild

strawberry and all kind of

common weeds. It is quite

daunting; I don’t know where to

start. Weed-whack them and

cover with black plastic? I don’t

want to use herbicides if I can

avoid it. Please help!

A: Weeds adore busy and

distracted people. Ignore a

garden for a week in this tropical

heat, and you will have

explosions of nutsedge,

galinsoga, sorrel and many other

fast-growing weeds. Unless you

can remove the “nuts” in the

rootzone of yellow nutsedge, it

will grow back. I suggest buying

a sharp weeding hoe or weeding

knife, which make fast work of

large areas. You don’t have to

weed the whole area in one go,

you can pace yourself over two

or three days. Just make sure the

cleared earth is then mulched to

avoid the weeds shooting right

back.

Q: I lost a dogwood that had

been just fine for 27 years since I

moved in to my home. It looked

fine in the spring, then all of a

sudden I noticed it was dead

several weeks ago. It is at the

bottom of a slope — maybe too

much water this year?

A: I think we are seeing the

delayed results of last year’s

record rainfall. In terms of a

replacement, you may want to

find a tree that will take wetter

conditions: bald cypress, black

gum?

Q: About four years ago, I

planted a then-tiny spicebush

and a small Miss Kim lilac next

to each other. To o close, as it

turns out. I had no idea how big

spicebushes get, and it is at least

seven feet tall and crowding out

the lilac! I’m assuming I am past

the point of moving the

spicebush successfully. Do you

think I’d have better luck with

the lilac? It is smaller. I am just

concerned their root systems

may be entwined by now.

A: Alas, neither of these shrubs

transplants well because of their

root structures. It may be a

question of picking one over the

other. Given our trajectory of

heat, I think I’d show Miss Kim

the door.

Q: I’m in suburban Maryland,

and most of the recent

thunderstorms have missed my

neighborhood; the ground is

really dry. I’m watering my

bushes and trees once a week

with a sprinkler or a soaker hose

for about two hours, but I

wonder if that’s enough.

A: When it turns dry, plants need

one to two inches of water per

week. It is important you give

the ground a good soaking once

a week or so, rather than a

sprinkling every day. You want

the soil to become fully wet

down to four inches, and you can

test for that by plunging a

screwdriver into the ground to

see how far it goes. Enriched soil

and mulches will retain moisture

better than unimproved clay, of

course.

Q: My emerald green arborvitae

is now half brown. Should it be

removed? Any idea why this

might have happened?

A: Conifers generally don’t

regenerate from dead wood. I

might take it out. This sounds

like it could be from bagworm

damage; look for camouflaged

cocoons. Bagworms are best

treated earlier in the season

before they get big and do a lot

of damage. It might also be root

rot from wet soil.

Q: We recently moved into a new

house that has a lovely large

window box. It is currently

empty, but the previous owners

used it year-round. Anything we

should know about planting in

window boxes? Is there

something we could plant now

for late summer/fall that would

look nice? We live right outside

the District.

A: Window boxes are much

more work here than in Europe,

where they abound. The first

problem is the use of insect

screens on windows in the

United States. The bigger

problem is the heat, which dries

out window boxes and hanging

baskets within a few hours.

Generally, the greater the mass

of soil, the better for the plants,

but such boxes get heavy with

water and need to be securely

anchored. On 90-degree days,

they will need to be watered

twice a day.

Q: I have to pull up two crape

myrtles succumbing to powdery

mildew. I would like to replace

them with a more resistant

variety. Can I plant the new

crape myrtles in the same spots,

or is that not a good idea?

A: You can find varieties bred for

mildew resistance. Powdery

mildew is a problem in corners

of the garden where there is poor

air circulation. This can be

mitigated by pruning in a way

that opens up the plant. But if

your site is enclosed by fences,

walls, etc., you may want to find

another plant for that location.

Q: My azaleas have become very

large and woody with big bare

patches. Is pruning effective for

controlling size, or should I

replace them? They used to be

petite and were much prettier

then.

A: This just in: Shrubs grow!

Please don’t think a plant at the

garden center is going to stay the

same size or anything close to it.

On old, big azaleas, you can

reduce the mass by trimming

them back, but don’t leave

branch stubs. Or you can keep

much of the height but take out

whole branches to open up the

whole structure. The key is to

bring an artistic eye to it and

study the plant from all angles

before cutting. If you think you’ll

botch it, don’t do it. Removing

growth now will remove some of

next spring’s flower show.

Q: I like to grow rattlesnake pole

beans each year in my raised bed

garden with chicken wire

around it. I never had a problem

before, but this year, after they

had grown so tall and beautiful

and were producing great beans,

something came along and bit

through the stem of each plant

about two to three inches above

the dirt line. I don’t need to tell

you how heartbreaking it is to go

out one day and find all the

plants drooping on the trellis.

Any idea what did this and how

to prevent it next year?

A: Sounds like a rabbit to me. It

might not be too late to plant

again (though those bunnies will

be getting hungry).

 Also at washingtonpost.com

Read the rest of this transcript at

live.washingtonpost.com.

GARDENING Q&A

Tackling droopy sunflowers, out-of-control weeds and more

Home

JENN ACKERMAN FOR THE WASHINGTON POST

Giant sunflower varieties such as Mammoth can grow to 10 feet or more and produce blooms the size of

a plate. The flowers tend to nod as the seeds develop in the central disk. Cut off diseased leaves.