Winter Gardening with Ed Rosenthal

Click here for part II of Ed’s Winter tutorial. 

It’s
mid-January, and here in San Francisco’s East Bay the weather is mostly cloudy
with a high of 63 and a low of 45 degrees. The same weather is forecast for the
next five days. This doesn’t sound like the most conducive weather to grow cannabis
outdoors. However, during much of the mild winter the sun shines and the
temperature climbs into the 70s, though it still drops to between 20 and 25 degrees
nightly.

I
have a small greenhouse that is surrounded on three sides by building walls.
Light is admitted only from the top and the southwest-facing side. The
greenhouse is kept moist to provide the right environment for tropical orchids
and for overwintering plumerias, the plants that produce Hawaii’s fragrant lei
flowers. A CO₂ generator controlled by a thermostat doesn’t allow
the temperature to slide below 60 degrees, within the tropical plants’ comfort
range and also very pleasant for young cannabis plants.

As
you can imagine, the amount of light entering the greenhouse is nominal,
especially this time of year, when the sun hangs low on the horizon. A quartet
of 55-watt T5 fluorescents hang over the orchids, and another 55-watt foursome
and a 100-watt fluorescent hang over the other plants, supplementing sun and
ambient light when it’s most intense.

My
plan is to grow on a table, below the canopy of the plumeria, which are partly
deciduous in this environment—they lose a lot of their leaves if the
temperature falls into the low 50s. Some light will get through, but it will
need to be supplemented. I decided to use a 75-watt white diode LED fixture
that is installed to hang below the plumeria, only 12 inches over the canopy.

I
bought three clones—Fire OG, Purple Kush and Candyland—from a local dispensary
and kept them for two days on a table that received daylight in the kitchen.
The lights were turned on throughout the day and evening so the plants were
kept in vegetative.

The
clones had been rooted in two-inch rockwool cubes. I planted both of them in
soft-cloth containers that I had used briefly during a previous experiment.
Wicks had already been installed in the five-gallon bags, and they were already
filled with barely used planting mix. This certainly reduced time spent
planting. I positioned each cube so its top was slightly raised from the
planting mix and the stem would stay dry, discouraging pathogens. Then I
watered the mix with a dilute vegetative fertilizer to help bond it with the
cube.

For
now, I placed a styrofoam board on the cold cement floor as a temperature
barrier. Then I placed the planted containers on the board and turned on the
LEDs. Unlike the other lights in the greenhouse, these lights will remain on
continuously for a few weeks to encourage plant growth and to keep the plants
in the vegetative stage, rather than switching to flowering, which is induced
by long nights. In a few weeks the lights will be turned back and the plants
will flower. When the clouds clear I plan to take the plants out for direct sunlight.

TIP
OF THE MONTH FROM ASK ED®

Do
you have an unobstructed south-facing window? During the winter it receives
plenty of sunlight as the light falls sideways, piercing the window and probing
inside. Just place potted cannabis plants or even a small hydro system there.
You can add supplemental light from a fluorescent or LED. Break up the night
with light to keep the plants from flowering. To flower the plants make sure
they have 12 hours daily of uninterrupted darkness. Then the plants will flower
and the buds will ripen in 55 to 70 days.