Agriculture Reference
In-Depth Information
that is easily achieved in your home as well as being within acceptable
ranges for all of your plants. Night and day temperatures should differ
by 5°F to 10°F (3°C to 5°C) with night temperature being the lower. For
most warm-season crops like tomatoes, eggplants, peppers, and cucum-
bers, a temperature range of 60°F (16°C) night and 75°F (24°C) day is
suitable. For cool-season crops like lettuce night temperature should be
about 55°F (13°C) and during the day (light period) 60°F to 65°F (16 to
18°C).
Herbs can withstand a very broad range of temperatures. They will do
best, however, at a range similar to that of tomatoes. Under too low tem-
peratures growth will be slowed, whereas under too high temperatures
the plants will get “leggy” resulting in soft succulent plants with little
fruit formation. In tomatoes the appearance of purple coloration on the
undersides of the lower leaves indicates temperatures are too low.
Keep in mind that your lights will also give off heat, raising the tem-
perature near the plants. Locate lights above the crop sufficiently to get
the necessary intensity without adding a lot of heat. You can purchase a
thermograph to monitor the temperatures on a 24-hour basis. Each chart is
good for one week. These instruments are better than a maximum-mini-
mum thermometer having high and low indicators that only tells you what
was the maximum or minimum. It does not tell you the fluctuation of the
temperature over time, as does the thermograph.
LIGHT
Plants have evolved under natural sunlight. To date no ideal artificial light-
ing can provide the same quality or quantity of light that the plant would
receive under natural sunlight. I wish to outline some types of artificial
lights that are available for use indoors so that you may better understand
what may be the best for your conditions and the plants you wish to grow.
As mentioned earlier you want a minimum intensity at leaf surface in the
upper portion of the plants of 5500 lux (510-foot candles) for a period of 14
to 16 hours per day.
TYPES OF LIGHTS
In the past, fluorescent lighting was the most common form of plant sup-
plementary lighting. Some companies promoted Gro Lux lamps specifi-
cally for plants. I usually found that cool-white high-intensity fluorescents
were the best and cheaper than the plant grow lights. Today, however,
lighting for plant growth has become more sophisticated. Most lights sold
today are of the high-intensity discharge (HID) type. There are two types
of lights: high-pressure sodium (HPS) and metal halide (MH). Usually a
