Summer
officially arrives later this month along with the longest day and the
most intense sunlight. Even the most sun loving Orchids now need protection
from the midday radiation. Heat
and light also mean that plants are using more water and growing at
rates not seen for many months. No
matter what kind of Orchids you grow, now is the time to increase water
and fertilizer.
Most
Cattleyas have new growths developing.
Be careful as you apply fertilizer not to overuse Nitrogen, as
it will lead to weak growth that is susceptible to rots later on. What is a high N fertilizer? Generally if the first number in a fertilizer
formula is the highest of the three it is considered high N. For most fertilizers, the first number is deceptive
because it describes total Nitrogen instead of useable N. If the formula says 30-10-10, the implication
is that there is three times the available N compared to the second,
which is Phosphorus. If, however,
the N is composed mostly of Urea, then the number is lower because Urea
is not directly available to Orchids and only becomes available if bacteria
associated with the media convert it to other forms.
In
the past, fertilizers I have used with even numbers have led to poor
growth because they actually contained little available Nitrogen. Look for fertilizers that contain either Nitrate
or Ammonia, as these are directly available to Orchids. The most important point is not to use fertilizers
in concentrations too high and to flush thoroughly once a month, especially
in the summer. Use fertilizer
weakly, weekly for best growth.
Repotting
can be safely done for most Orchid genera with the exception of a few
tricky species. The ideal time
to repot is always when plants are growing so that they will be reestablished
with fully functional root systems when fall arrives.
Some Orchids flower in summer, leaving novice questioning if
they should repot. A healthy
plant can be repotted while flowering and may need to be repotted then. Cattleya bicolor is usually in bloom when it begins to grow
new roots. This and most other
bifoliate Cattleyas must be repotted when they get new roots, even if
in flower.
Last
year, I had several Paphs in flower when repotting was done. Several were repotted while in flower and others
left in the pot and were repotted when they finished blooming. A third group was left in the pot and a teaspoon
of lime added on the surface of the media. The first two groups were similar in growth and flowering a year
later, while the last was clearly harmed by being left an additional
six months in the same media. Different
media may yield different results, but clearly repotting when in flower
did no harm.
Vandas
and similar genera are in their glory now with high temperature and
humidity. Several years ago,
I discovered that Rhynchostylis species and hybrids close to these species
preferred to be shaded more than their vandaceous cousins during the
heat of the summer. Other cool
loving genera can also stand more heat if light levels are reduced.
Spider
mites have ceased to be a problem unless you grow inside where air conditioners
reduce humidity. Unfortunately,
scale, mealybugs, and other pests reproduce rapidly and need to be controlled. Rusts (related to fungi) affect a few genera
of Orchids and appear on thin-leaved orchids such as members of the
Catasetum group. It can be controlled
with sprays, but is less of a problem if good air circulation and water
low in solids are provided. It
is important to address problems quickly this time of year as pests
multiply rapidly along with
your Orchids.
Orchid
growers, like many others, are interested in using less pesticides and
continually looking for natural ways to control pests. Greenhouses contain an array of insects and
other animals, some of which are pests and others that are simply enjoying
greenhouse conditions. The presence
of frogs and toads suggests that there is an adequate food supply of
insects. Are pill bugs an important pest? What about roaches? Most insects have some potential to cause damage
and must be watched, but the presence of a greenhouse totally free of
animal life is more disturbing than the pests themselves. The trick is to find that happy medium.
Almost every year a “new” treatment
emerges that is theoretically less harmful to the environment. One year it was light oil, the next Neem oil
and so on. The introduction
of each new product initiates a flush of excitement that becomes tempered
with reality within a year or so. Each
new product seems to work well under certain circumstances, but none
has proven to be the “magic bullet” that will solve all orchid
growers problems. No matter what new product comes along, the
best approach is to maintain healthy conditions with good air circulation,
adequate spacing, appropriate humidity, and constant vigilance.