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Winter losses
Hostas are among the sturdiest plants
I've ever grown, and fortunately, we seldom have any losses. But
all living things can have their problems, and if you are going to lose
a hosta, it's probably going to happen over the winter or very early
in the spring.
If you've lost one or more hostas
over the winter, it's probably easier than you think to determine the
cause. As far as I know, and I've been growing these things for almost
30 years, there are no chronic diseases that will suddenly kill a
hosta. Those few pests and diseases that hostas might contract, like
nematodes, fungus diseases, and viruses, are generally an obvious
problem with obvious symptoms years before they can kill a plant. Many
of these pests and pathogens lead only to leaf damage and do not kill
the plant.
Obviously there are things like
accidental herbicide poisoning, a dog that waters your hostas every
day, etc., but aside from these things that would be unique to your
experience, there are only two significant causes of winter losses.
The first is voles or other rodents
feeding on the plants from underground. You may think you don't have
voles, but unless you know what they are and how they live, and have
actually looked for them, don't make that assumption. Voles are very
small, short-tailed field mice that live underground and about the only
time you will see one is when your cat brings you a dead, furry
present. They are very common in all areas, but because they burrow and
live underground, most people never see them. Voles consider the
starchy rhizome of a hosta a delicious treat, and they can destroy a
plant or a whole group of plants in a very short time. Voles have to
find your plants before they can eat them, so you may grow hostas for
several years with no damage and then one year, they're gone. Vole
damage is much more common in the winter than at any other time of year.
When we first moved our nursery here
a couple years ago, the previous owner of the property had a few mature
clumps of hostas scattered around the house. These plants had obviously
been here a while, so I assumed that voles were not a major problem. We
were way too busy that first year to do much planting but I decided to
put in a small hosta garden to get started. In the spring I found the
entire area was undermined with vole runs and out of about 25 hostas,
not a single plant was undamaged. I don't know why her plants survived, but
the area was infested. We are trying again this year, but only after a
serious eradication effort.
Essentially, voles are just mice that
live underground, and control measures generally the same as those for mice
anywhere, traps, poisons, or cats. You just have to be careful that
your efforts do not harm pets or other wildlife. Newer methods, such
as noise makers and castor oil sprays are also sometimes recommended, but I
don't know if they actually work or not. And lastly, you can use wire cages
or other barriers to surround the roots and stop the voles from tunneling to
the rhizome. There are a number of web sites that
provide information on vole control. Just use your favorite search
engine.
The second possible cause of winter
loss is crown rot,
and it is a bit more complicated because it can be caused in several
ways, but almost always by water, either too much or too little, or by
freezing temps at the wrong time, or a combination. First the
water factor. Usually the problem is too much water in the winter. In heavy soils,
without good drainage, the plants often stay too wet in the winter
and rot sets in. Hostas love water when they are actively growing, but
not when they are dormant. Occasionally, crown rot can also be a
problem if the plants do not get enough water in the fall and are
stressed when they go dormant.
The solution to this problem is to insure
that your hostas are planted in well drained soil. If you natural soil is
heavy clay, you should add as much compost as your back will allow. If
you can't incorporate compost into your soil, you can add compost and
topsoil to form raised beds so the water can drain away from the rhizome.
Be careful with raised beds, because piling soil on top of tree roots can
smother and kill a tree.
Crown rot can also be caused by a
late spring freeze. Hostas are extremely hardy and can withstand very
cold winter temps, as long as they are dormant. Things are different
when the plant starts growing in the spring. Once the plant begins
active growth, a late freeze can damage the plant or even kill it. Some
varieties, like plantiginea or montana 'Aureomarginata',
break dormancy very early in the spring and are difficult to grow in
areas where late freezes are common. Virtually all hostas are
susceptible to freeze damage, but the early risers tend to be hurt more
often. Blue hostas seem to be especially susceptible to such damage.
If freezing temps occur after the
leaves unfold, even a light freeze can turn the foliage to mush. Plants
damaged by a light freeze will usually recover by summer. A hard freeze
can be much more serious, and can lead to crown rot even if the leaves
are still tightly furled and only the spear is showing.
So, if you're not sure what happened, how can you tell why your plant died?
The best way is to dig the plant and inspect the rhizome. It won't
hurt the plant, and if you have many hostas in the same area, you should
find the cause of the problem before you lose them all.
If
you dig up the remains and find that the plant is still there but the
rhizome has turned mushy and the roots are brown and pull apart easily,
the plant has rotted. On large plants, you may find that some of the
rhizome is still firm and if you cut away all of the rotted flesh and
dip the healthy part in a 10% bleach solution for a few minutes, you may
be able to save something of the plant. If the whole rhizome is mushy,
there is no hope of saving it.
If you find that the rhizome is not
there any more, or if part of it has been eaten away, you have voles.
Plants that rot take a while to completely decay and disappear, so if
there's nothing left, it's been eaten. Sometimes you don't even have to
dig the plant, you can just stick your finger in the soil where it used
to be and you will find the tunnel that the voles used to reach you
hosta.
There are limits to what you can do
to prevent winter losses.. The problem is, losing plants to things
like this is just part of gardening. You can't control nature.
But there are things you can do to limit the risk.
Obviously, you cannot stop late spring
freezes, but you may be able to protect your plants from damage.
If your hostas have broken through the soil surface and a freeze is
coming, you should cover them with an insulating material. Nurseries
generally use large cloth or plastic foam blankets specially made to
provide several degrees of protection, but for hostas in the garden,
covering individual plants or small groups is usually more practical.
Spring freezes often last only a few hours, so if you can provide an
insulating barrier between the outside air and the warmer earth and
plant, you can usually prevent damage. Anything from loose dry leaves to
an overturned box or bucket with a weight on top is suitable.
Try to keep the cover from touching the foliage, especially if you are
using plastic sheets, so that there is an insulating air space between
the cold air and the foliage.
If your plants are hit by a frost despite
your efforts, there is nothing to do but cut off the mushy leaves and wait
for them to regrow. I suggest waiting a couple days before you cut
them back because after a light frost the leaves will sometimes appear to be
damaged but will recover after a bit of warmer weather.
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