Rose
Care 5-09-08
By Gary Matsuoka CCNP
Laguna
Hills Nursery, Inc.
71 Auto Center Drive
Foothill
Ranch, California 92610
(949) 830-5653
Placement
Most
roses, especially the popular hybrid teas, perform best with
full sun. Many
landscape and antique varieties will do fine in some shade.
Diseases can be minimized by keeping roses far apart,
away from walls, or from anything that can block air
circulation. In
a row of hybrid tea, grandiflora, or floribunda roses, 3
feet is the recommended minimum spacing between plants.
Closer spacing promotes pests and diseases.
Rose plants perform very well planted singly in the
landscape.
Soil
Roses
can tolerate and perform well in poor soil but grow most
vigorously when the soil has great aeration.
Soil is best aerated by incorporating pumice, sponge
rock, decomposed granite, or coarse sand.
Rice hulls and peat moss can also help.
Laguna Hills
Nursery Planting
Mix (containing pumice and peat moss) gives excellent
results at 1 sack for every 5-10 square feet of rose bed.
Compost
and organic mulches (Harvest
Supreme and
other commercial planting mixes) belong in a 2-3 inch
thick layer on top of the soil. Decomposing organic material is the energy source to keep
soil alive, but will eventually damage or stunt root
development if incorporated into the root zone.
Many
serious rose enthusiasts will grow roses in raised beds.
The soil in raised beds is naturally well aerated
which results in accelerated growth and easier maintenance.
Roses
also perform well in containers.
Miniatures require containers at least 8 inches wide.
Larger roses should have containers at least 18
inches wide. Our
Laguna Hills Nursery Potting
Soil Acid Mix is an excellent soil for containers.
Water
Roses love water.
Roses can be irrigated by hand or using sprinklers,
bubblers, or drip irrigation.
During warm weather water at least every 2 days.
Daily irrigation is fine.
A mature rose bush may use 2 gallons of water on one
hot day. Mid
morning to noon is the best time to water because we want
the leaves to dry off quickly (minimizing disease problems).
During the hottest days of the year sprinkling the
rose plants at noon is helpful.
Many large rose gardens use sprinklers for a short
period every day. The
force of the water knocks insects and mites off the foliage
and actually inhibits diseases as long as it dries within a
few hours.
Fertilizer
The easiest and best long-term way to feed roses is
with organic fertilizers.
Organic fertilizers feed the soil and the soil then
feeds the roses. Chemical
fertilizers feed the plants directly and the soil becomes
sterile. Over
the years chemical fertilizers are difficult to balance and
the plants often become chlorotic.
The most accurate chemical fertilizer is probably Grow
More Magnum Rose
Food, which was created for the famous rose garden at
Rose Hills Memorial Park in Whittier.
At our store we have used Dr.
Earth Rose and Flower Fertilizer (100% organic), E B Stone Rose
and Flower Food (100% organic), and Gro-Power All Purpose Fertilizer. At
my own home I will often use chicken manure.
In a well-established organic garden, a dressing of
rich compost is sufficient.
Pest Control
Aphids
are the small, olive to amber-colored, lice-like insects
that appear in large colonies on the new growth.
They usually make an appearance in late winter and
early spring. Heavy
infestations cause malformed leaves and flowers and cover
the foliage with sticky honeydew.
Aphids are eventually controlled by natural predators
(ladybeetle, syrphid fly, and tiny parasitic wasps) and
generally aren’t a problem following the first bloom
cycle. If you
can’t tolerate their presence they are best killed by
applying either Bayer Rose and Flower Insect
Killer (spray) or
Spectracide Immunox. We don’t recommend the systemic granular products because
of their high toxicity.
A sharp stream of water, oil sprays, and soap sprays
are somewhat effective.
Flower Thrips
are small sliver-size bugs that feed on opening flowers and
cause warping and browning of the outer petals.
Damage is most severe on light-colored roses
mid-spring to summer. Control
a bad case of thrips by cutting off and discarding all open
flowers at one time and then spraying all opening buds (just
as they show a crack of color) with Bayer
Rose and Flower
Insect Killer (RTU) or
Spectracide Immunox (RTU). Spinosad
is a new organic spray that may be just as effective. Treating the opening buds for two weeks usually ends the
thrips attack for the year.
Rose Slug
is actually the caterpillar-like larva of a wasp-like insect
called a sawfly. These
larvae skeletonize the leaves in mid-summer creating a
lace-like pattern. These pests are common along the coast and may infest inland
gardens at times. Rose
slug is easy to kill with just about any pesticide, however
there are many generations during the year and a long
lasting pesticide like Bayer
Rose and Flower
Insect Killer (spray)
is less labor intensive.
Spinosad is
a new organic spray that can provide short term control.
Spider Mites
are tiny spiders that are often found on the backside of
older leaves late spring through fall.
The leaves become dusty and gray green often with
brown margins. Spider
mites inject toxins as they feed and the plant will stop
growing and blooming under heavy infestations.
Plants with heavy infestations should be stripped of
leaves and sprayed with a sharp stream of water every week
for a month, or treated with a horticultural oil.
Spider mite outbreaks seem to only occur following
use of Orthene, Isotox, Orthenex and Sevin.
Avoiding use of these products is wise.
Cane Borers
are insects that find freshly cut stems and drill into the
pith causing dieback. The
damage isn’t severe, but can be prevented by putting a
drop of household white glue or fingernail polish or pruning
tar on the cut stems.
Grasshoppers,
Caterpillars, and Fruit
Beetles often eat large holes in developing
flower buds. Use Spinosad or Bayer
Rose and Flower Insect Killer to treat.
Disease Control
Powdery Mildew
is an external fungus that covers newer foliage with a
white or gray mold. Our
high humidity and moderate temperatures that occur between
April-July and October-November promote mildew.
Powdery Mildew spores germinate under dry, but humid,
conditions. Favorable
conditions for mildew are 40-99% humidity and 60-80°F.
Mildew doesn’t like rain.
Untreated foliage becomes warped and permanently
damaged. Severe
infection causes cessation of growth and blooming.
When the mildew has been on the foliage for more than
10 days it is best to trim off the affected foliage.
More recent infections can be cured by applying Green
Light Rose
Defense, which is a vegetable oil, or E-RASE
(Jojoba oil) which is less likely to burn foliage of
sensitive roses.
A
similar excellent cure was developed 80 years ago by Cornell
University. Mix
2 teaspoons of Baking Soda and 2-4 tablespoons of a
horticultural or vegetable oil (Canola oil or Summit
Year Round Spray Oil) in 1 gallon of water with a
wetting agent (Monterey-Nature’s Own Spray Helper
or a few drops of dish soap).
Keep shaking the solution so that the baking soda
doesn’t settle. Apply
every week to susceptible rose foliage.
We used this formula in our store.
Longer
term control can be achieved by using chemical controls like
Bayer Disease Control or Spectracide
Immunox. Serious rose growers may wish to use fungicides like Banner
Maxx or Compass, which control most rose diseases for 2-3 weeks.
Rust is a fungus that causes leaves to turn yellowish and
develop powdery orange spores on the reverse side. There are actually several species of rust and the spores can
be orange, red, or black in color.
Rust fungus can attack leaves that remain wet for 2
hours or more during mild weather. Rust spores travel by
air. Rust
spores germinate at temperatures between 59°F
and 70°F.
Spores start dying when temperatures exceed 82°F.
Besides rain and drizzle, overhead irrigation before
8am or after 2pm can cause infection.
Cutting off all the infected leaves can eliminate
rust. The
products that are most effective at preventing and curing
rust are Banner Maxx and Compass
mentioned above. Bayer
Disease Control
and Spectracide Immunox may also provide protection.
Because
rain is the primary cause of rust, I delay winter pruning
the roses at my home until April.
Since most of our stormy weather is over by then, the
new growth that emerges a few weeks later will not get hit
by much rain. Using
this method I will only have to strip my rose plants once
per year, plus they have been blooming all winter.
Black Spot is a fungus that creates large fuzzy black spots
and yellow patches on mature rose leaves.
Black Spot, like rust, attacks wet foliage. Black Spot spores germinate if covered with water for at
least 7 hours. The
disease causes most trouble at 64°F
to 79°F.
Temperature above 86°F
kill germinating spores.
Spots form 10-20 days following germination.
It can be cured and prevented using the same
techniques we utilize for control of Rust.
There was no Black Spot in Southern California until
the early 1990’s.
Downy is a fungus that causes rose foliage to turn yellow and
fall off. Downy
attacks roses during cool wet weather.
Downy spores germinate if covered with water for at
least 4 hours, but may germinate in high humidity also.
Downy can operate at temperatures between 41°F
and 80°F.
Defoliation can occur in as little as 3 days.
It often causes permanent damage to rose canes.
Damaged canes show red or purple lesions in the shape
of blotches, bands, or cracks, or as a ring surrounding
attachment points of branches and leaves.
80°F
weather halts the disease, however, stems showing lesions
should be cut off below the infected areas.
Agri-Fos is the best fungicide to stop and prevent infection and is
relatively non-toxic. Downy
first appeared in Orange County in the mid 1990’s.
The majority of homeowners never see Downy.
Rose Mosaic Virus is a disease present in many roses.
It is visible as irregular yellow or cream mottling
of the foliage. It
can lower the plant’s vigor, especially during cool
weather. Symptoms usually disappear during summer.
It is virtually impossible for an infected plant to
transmit Mosaic virus to an adjacent rose. It cannot be cured, but is less noticeable in vigorous
plants. It is
often not recognized until a plant encounters less than
favorable growing conditions.
Fortunately most of the roses currently being soil
are virus free.
Anemic Rose Replant Syndrome occurs when new roses are
planted in old rose beds.
The soil in established rose beds is filled with
countless small rose roots.
Disturbing the soil to plant a new rose will sever
and kill a large number of roots.
These dying and decaying roots will seriously affect
the health of the new rosebush for 2-5 years.
Unrelated plants will not be affected.
To avoid the problem replace the soil about 8-10
inches deep and 2-3 feet wide with soil from a distant part
of your garden, or purchase sandy loam in bags or bulk, or
use a few sacks of our Laguna
Hills Nursery Acid
Mix.
Applying Pesticides
Our goal is to apply as little chemical as necessary
to keep our roses looking good.
Many pesticides are available in ready-to-use (RTU)
containers. These
may be adequate for rose gardens of less than 20 plants.
For larger gardens it is less expensive to purchase
pesticides in concentrate form and a sprayer to apply them.
The most accurate sprayers are the pressure sprayers
(hand trigger sprayers and hand, electric or gas powered
pressurized tank sprayers).
Hose-end sprayers are quite inaccurate.
To mix your own pesticide solution add half of the
water to the tank first. Add the pesticide concentrate followed by a spreader sticker
(Monterey-Nature’s Own Spray Helper).
Then add the rest of the water.
Shake, pressurize, and apply.
Do not leave chemical solutions in the sprayer for
more than one day.
Sprayers should be rinsed 3 times with water after
use. Any
leftover chemical or rinse water should be applied to the
soil in the garden. Store
sprayers in a dark closet, otherwise algae could grow in the
tank. Do not use the same sprayer to apply herbicides.
Always follow directions on the product label.
Pruning
Dead Heading
Any rose will bloom more if the spent blooms are cut
off (dead headed). There
are many methods rosarians utilize for different kinds of
roses, but none are clearly superior.
The most common rule used is to cut the stem with the
spent bloom down to just above the highest 5-leaflet
leaf. (A rose
leaf consists of a leaf stem connected to 1-7 pinnately
arranged leaflets) The
leaves closest to the flower usually have fewer than 5
leaflets.
If you want the most flowers possible just remove the
spent flower. Plants
pruned lightly will bloom heavier with smaller flowers.
If you want the biggest flower possible, cut the stem
down to just above the lowest 5-leaflet leaf on the
stem. The more
severe a stem is pruned the longer it takes to develop the
next bloom. The
largest flowers occur on canes that originate near the base
of the plant. The
largest flowers also develop during cool weather when growth
is slow.
Rose plants grow taller all year as they branch
upwards off of the lower canes.
By late summer the stems should be cut into older
growth below a branch point to keep the bush compact.
Because our local climate is so mild a rose plant can
be pruned heavily any time of the year.
Winter Pruning
Traditionally in Southern California modern roses
have been pruned heavily and stripped of all foliage in
winter. Although
locally grown roses rarely go dormant (every so often we
will have a cold winter period with night temperatures in
the 20’s and 30’s) the “winter pruning” is performed
to eliminate all diseases and pests at one time and create
an esthetically pleasing (more compact) form.
In colder climates roses are pruned after the snow
melts in the spring. The
instructions given in most modern texts make more sense in
harsher climates where you would be faced with many dead and
dying branches following the spring thaw.
In our mild climate, unless there is a bad pest
problem, rose plants can be shortened one portion at a time.
In my own garden I now do my “winter pruning’ in
spring, but I remain flexible. About every 10 years we’ll have a frost that defoliates the
bushes in December or January and I’ll prune at that time.
Sometimes there is a bad wind in fall that strips off
all the foliage. If
fall or early winter rains are heavy, the foliage is often
so badly diseased with rust that I’ll prune in January.
In a typical year I’ll allow my roses to keep
blooming during the winter months, dead heading normally.
During cool weather my roses often produce their most
spectacular flowers. Between
mid March and mid April, when my roses have just finished a
bloom cycle, I will do my “winter pruning” using the
following steps:
1)
Roughly prune each plant to the desired height.
I prefer to cut hybrid tea roses down to 12-18”
(shorter canes promotes fewer, but larger flowers),
floribundas to 24”, english roses to 30”, and leave
climbers full length. The
final cut should be just above a bud facing the direction
you wish the new growth to go.
2)
Remove small, branched growth that isn’t producing
flowers.
3)
Remove canes or portions of canes that show disease
lesions.
4)
Provided there are enough canes to keep the plant
roughly symmetrical, eliminate the oldest ones.
We like to start the new season with 3-5 canes on a
hybrid tea, more on other rose types.
On climbers, remove canes older than 3 years.
5)
Strip off all diseased or infested leaves.
6)
Clean up the rose bed.
I remove all the old mulch, fallen leaves, and
shriveled petals that were covering the soil.
7)
Fertilize. Some
years I’ll dress the entire bed with a dusting of chicken
manure. Alternate
years I’ll use Harvest
Supreme.
8)
Cover with a new layer of bark.
My favorites are Bark
Mulch, Xerimulch, and
Cedar.
9)
Sprinkle everything lightly, but thoroughly to settle
the mulch.
10)
There is no need to use a dormant spray.
Lime sulfur is supposed to help sterilize the bed,
but apparently is not effective.
Most disease spores travel through the air.
Calendar
of Pests & Diseases
During
the warmer months of the year there are certain pests or
diseases to expect
.
January
none
February
none
March
Rust and Aphids
April
Flower Thrips and Rust
May
Mildew, Flower Thrips, Rust
June
Mildew and Rose Slugs
July
Rose Slugs and Grasshoppers
August
Rose Slugs and Grasshoppers
September
Rose Slugs and Mildew
October
Rust and Mildew
November
none
December
none
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