Temperature Zygopetalums are
the among the easiest of the orchids to grow
outdoors in southern California, particularly
along the coast and up to 15 or 20 miles inland,
and are perfect companions for cymbidiums.
Zygopetalums grow best under partial
shade-partial sun conditions. Zygopetalums can
tolerate considerable summer heat and winter
chill without damage. Many growers leave their
plants outdoors all year long. Temperatures up to
100 degrees F for short periods such as we
encounter in a Santa Ana will not harm the plants
although buds may drop on some susceptable
plants. Buds and flowers may be damaged if the
temperature drops to 29 degrees F but the leaves
and bulbs can usually withstand 29 degrees F
under shadecloth for a few hours. For
temperatures lower than this, some protection
will be required.
Light Adequate light is the
most important factor to grow and flower
zygopetalums well. The plants grow best with 3000
to 4000 or more foot candles of light intensity
as measured with a light meter. 50% lath covering
or 55% to 63% shade cloth overhead provides this
light intensity under most conditions. Plants
grown outdoors will generally be a little more
compact and will have tougher leaves than they
will when grown indoors. Locations inland may
need more shade during the summer to keep the
plants from burning. During the summer, the
leaves should be a yellowish green, not a deep
green. Plants grown in too much shade will
usually be a lush green and will often not flower
well. Providing additional shade after the
flowers open will hold the color and increase the
flower life as well. If you provide extra shade
for the flowers, remember to remove it when the
flowers fall so that the plant will grow best for
next year.
Watering Zygopetalums like
lots of water and prefer to be constantly moist,
but not wet. During the growing season, water
thoroughly at least once a week, more often in
warmer or drier locations. The amount of water
will depend on the potting mix and the water
quality. Rain water or demineralized water will
give the best results, but water that contains
large amounts of dissolved salts such as the
Colorado river water we have in Southern
California or hard well water can also be used.
Open or porous mixes needing more water than a
heavy dense mix that retains a lot of water.
Water thoroughly so that water runs through the
pot and out the bottom. Watering heavily so that
excess water flows through the potting mix is a
process called leaching which helps to keep the
excess salts from Colorado River water or hard
well water and fertilizer from building up in the
potting mix. Excess salt buildup may cause the
leaf tips to die back and the leaves to fall
prematurely. Letting the plants dry out and not
leaching will cause the leaf tips to die back
faster. On hot days, the plants benefit from
overhead misting or sprinkling to lower the
temperature and increase the humidity in the
growing area. During the winter, zygopetalums
need less water, but should never be allowed to
dry out completely. Watering every 2 or 3 weeks
may be adequate, even with no rain.
Feeding and Fertilizer
Zygopetalums are moderate feeders and will do
well with the same fertilizer growers use for
cymbidiums. Many growers use a high nitrogen
fertilizer during the growing season (February to
August) and a low nitrogen fertilizer during the
blooming season and winter. Others get
satisfactory results with a balanced fertilizer
all year long. Fertilizer is available in both
water soluble and slow release forms. Most
growers use a water soluble fertilizer such as
Peters 30-10-10 Orchid Special or Miracid during
the growing season ar a rate of one teaspoon to a
gallon of water and Hi Bloom or similar low
nitrogen content water soluble the rest of the
year. Many amateur growers use a Hozon or
Siphonex to siphon a fertilizer concentrate into
a hose to use with a watering wand. Others prefer
to use a slow release fertilizer such as Osmocote
sprinkled on top of the potting mix. The slow
release fertilizers work well where sprinkling
systems are used to water the plants. Watering a
slow release fertilizer with a watering wand can
wash the fertilizer granules off the plant so use
care. The slow release fertilizers may be
available with 3, 4 or 6 month release times. I
would recommend that the amount be cut in half
and the application be made twice as often. This
compensates for the tapering off often seen with
the slow release fertilizers. If possible, it is
better to use one of the newer "lite"
fertilizer combinations such as the Peters
Peatlite formulations that does not contain urea
as a nitrogen source. Urea requires a bacterial
or chemical reaction in the potting mix to
convert it to the nitrate form before the
nitrogen is available to the plants, and much is
washed out with subsequent waterings before it is
converted.
Pests and Diseases The giant
white fly and scale are the two most persistent
zygopetalum plant pests with snails and slugs as
the principal flower threats. The giant white fly
can be controlled with an insecticidal soap. Wipe
off as much of the colony as possible, then spray
the underside of the leaves well. Scale in the
leaf axils can be a persistant problem that is
hard to eradicate and the use of a good systemic
insecticide may be required. Slugs and snails may
be controlled with the available snail and slug
baits, or with a big foot and a flashlight at
night. Aphids may be attracted to buds and
flowers, but are not usually a serious pest. Do
not use an insecticidal soap or an insecticide
spray with a spreader sticker on zygopetalum
buds. We have seen severe deformation of buds and
flowers as a result. There is no toxic reaction
to the plant itself and such materials may be
used when buds are not present. In general, any
insecticide should be applied during a cool,
shady time of day such as early morning to
minimize any potential reaction.
Zygopetalums are relatively resistant to
bacterial and fungal diseases. Bacterial and
fungal diseases may be a problem under wet and
crowded conditions. Adequate spacing of plants on
the bench and watering early enough in the day so
that the plants can dry out before dark is the
best prevention. Zygopetalums can be susceptible
to the common orchid viruses. Virus infection of
a zygopetalum may be caused by insects feeding on
an infected plant and then moving to an
uninfected plant, but transmission with
contaminated tools during dividing, potting or
cutting the flowers is usually the cause. Always
sterilize tools and the work area before dividing
or repotting each plant, and use disposable
rubber gloves or wash hands thoroughly after each
plant.
Potting and Dividing
Zygopetalums like a slightly acid potting mix
that provides good drainage. Most growers use a
fine orchid bark mix with 20% sponge-rok or
perlite added. Sand, coarse peat and redwood bark
or shavings may be added to improve the water
retention in inland locations. Straight seedling
orchid bark (1/8 to 1/4 inch) or medium orchid
bark can also be used. Zygopetalums are usually
not grown with larger grades of bark, but can be
with more water.
Zygopetalums generally need to be repotted
about every three years under normal conditions.
Zygopetalums should be repotted just after the
old blooms have fallen off. If the old mix is
broken down, the plant should be repotted as soon
as possible to minimize root rot. Broken down mix
tends to hold too much water and will reduce the
air movement around the roots which often causes
the older roots to die back. Vigorous plants will
often outgrow the pot before the mix starts to
break down. When a zygopetalum fills the pot and
starts to grow against the edge, it should be
repotted even if the mix is not broken down.
Potbound zygopetalums may be underwatered which
can reduce the vigor and blooming capability.
When dividing and repotting, try to keep
divisions with 2 or 3 green bulbs and perhaps one
backbulb if you can. Select a pot large enough to
allow 3 years growth. For most zygopetalums, a
pot which allows 2 inches of room in front of the
lead growth is the proper size. Divide plants by
breaking apart at the natural divisions. If
necessary, use a sterilized knife to separate the
bulbs. Clean the old potting mix from the roots
and remove any dead or damaged roots. Dead or
damaged roots can encourage root rot in the new
mix. Place a mound of moist potting mix in the
center of the pot. Spread the roots over the
mound of mix and work mix in among the roots. Do
not ball the roots in the center of the pot. The
lower 1/3 of the bulbs should be covered with
mix. Tap the pot firmly on the potting bench to
help settle the mix around the roots and press
the mix firmly around the edge of the pot with a
potting stick (I use a hammer handle or a piece
of 1/2 or 3/4 inch PVC pipe). The mix should be
tight in the pot, not loose. Mix that is too
loose in the pot will not provide enough support
for the roots and also tends to decompose more
rapidly.
All potting tools, knives or shears and
potting sticks should be sterilized after each
plant to prevent the transmission of disease.
Tools may be sterilized by flaming with a propane
torch or by soaking in a 50% clorox solution ot a
saturated solution of tri-sodium phosphate (TSP)
for a few minutes. Don't forget to wash your
hands with soap and water also, including under
the fingernails. Better yet, use disposable latex
or vinyl gloves and discard after each plant.
Your hands can transmit disease from one plant to
another the same as dirty tools. Plants should be
handled or divided on a clean surface. Several
layers of newspaper can be spread on the work
surface and any that are dirty can be discarded
after working with each plant.
Care After Repotting After
dividing and repotting, the plants should be
placed in an area with heavier shade than normal,
and should be kept cool and slightly on the dry
side for several weeks. This encourages the
growth of new roots into the new medium. We water
the repotted plants after a day or so in the new
mix, and water the first time with a dilute
solution of Physan or Naccosan, which is a
bactericide and fungicide, to help reduce the
likelihood of fungal or bacterial disease in the
newly repotted plant. Watering with a dilute
solution of Subdue may also help control disease
after repotting. Use of an anti transpirant as a
spray or drench after dividing and repotting may
help reduce the moisture stress on a plant, but
we do not find it necessary under our conditions.
Special thanks to Casa
de Las Orquideas for the above cultural
information!