During the past year, I have subjected most of my orchid collection to a large-scale experiment regarding fertilizers and media. How much fertilizer does an orchid actually need to grow well and produce large flowers? For the entire year of 2011, fertilizer was applied at very low levels and only during the growing season, March-September. Fertilizer was applied (0.07 teaspoons/gal) weekly for three weeks followed by a week of just water to flush any mineral buildup.
My water is fairly high in dissolved solids and on the basic side.
Peters Excel 15-5-15 Cal-Mag provides additional magnesium and nitrogen
in the form of nitrate and ammonia, both of which are immediately
available to plants. This fertilizer also decreases the pH, which is
ideal for my water. Most fertilizers add nitrogen in the form of urea,
which requires bacteria and decomposing media before it is available to
orchids. Because I grow mostly in lava rock, urea is useless.
What I learned this year is that applications of fertilizer much lower
than recommended at a much greater frequency can produce excellent
growth and large flowers if there are adequate roots. During my
experiment, cattleyas well established in pots with a large root system
bloomed with as large and as many flowers as they did with higher
nutrients. They also produced nice new pseudobulbs at least at large as
previous bulbs.
However, cattleyas that were recently repotted or those that had less
developed root systems, often did not bloom or produced smaller flowers.
Recently repotted cattleyas grew new roots under this fertilizer
regimen, but not nearly as many as cattleyas that had large root
systems. This is problematic for newly repotted cattleyas because new
roots are important if the orchid is going to regain its previous
flowering characteristics.
There were a few cattleyas in the collection that were still in organic
media, albeit mostly old decomposing media. In general, these were doing
OK as long as the medium was not soft and holding water. Several of
these were bifoliates that are poor candidates for repotting unless they
are in the process of getting new roots. Occasionally, I miss that
period and leave them in the old medium.
This year begins a new experiment. One issue with using lava rock is the
space within that allows large “Cucaracha” (roaches) to live in the
pots. They emerge at night and eat new roots, flowers and even new
growths. The latest experiment is to cover the lava rock with a thin
layer of Aliflor. Aliflor is a round artificial rock-like medium. I
still have a totally inorganic medium, Aliflor and lava rock, but
roaches cannot move to the pot surface where new roots are found. This
allows the addition of Nutricote fertilizer because the small Nutricote
pellets do not fall through to the bottom of the pot. Over the years,
Nutricote has provided a well- balanced and continuous level of nitrogen
and other nutrients.
Repotting has begun early this year as warm conditions have caused new
roots and growth earlier this year. The sun is already getting stronger
so new growth now will just allow an orchid to grow more this year.