Cacti are fun to grow because of
their eccentric, even comical shapes. They are extremely beautiful especially
when they bloom. If your air is dry and you have trouble growing plants that
like high humidity, put away your mister and pebble-filled trays and try cacti
instead. They also need less attention than other houseplants. They are part of
the large group of desert plants called “succulents” which store water in their
fleshy leaves to get them through the long dry spells their native climates are
known for. Cacti don’t have conventional leaves, just stems, which are often
jointed. They also have “areoles” small holes from which tufts emerge.
Sometimes the tufts are soft, like hairs; sometimes they are sharp and spiny.
The tufts shelter them from the sun and if sharp, against creatures who might
bite them to get at the water inside. The flowers which appear in spring and
summer also emerge from the areoles. 
Cacti are a large family, with
several genera that make good houseplants. Here are some good ones to start
with Mammillaria cacti are sometimes called “pincushion” or “nipple” cacti.
Most look like small round globes covered with nipples and bear clusters of
small, pretty flowers in a crown around the top. Some good ones to try are old
lady cactus “Mammillaria hahniana” which is well covered with long white hairs,
produces red flowers and generally grows well under 10 inches; the tiny golden
star cactus “M. elongata” which is composed of a cluster of long projections
with yellow spines and white flowers; M. zeilmanniana, which forms a little
round ball and produces pinkish red flowers even at a young age.
Moreover, Easter lily cactus
(Echinopsis multiplex) is a little round cactus with vertical ribs and large,
pink flowers borne on tall stems; these open in the evening and have a lovely
fragrance. Hybrids, which are crossed with species of Lobivia cactus, come in
other colors such as red and orange, and may be day blooming. Among the many
other good flowering cacti to try are species of Opuntia “prickly pear”
Aporocactus “rattail”, Echinocereus “hedgehog”, Ferocactus “barrel” and Rebutia
“crown”.
One of the most popular cacti is
the Christmas cactus “Schlumbergera truncate or Zygocactus truncatus” a jungle
epiphyte that sends out long, arching jointed stems. Lovely red or white tube
shaped flowers dangle from the tips around Christmas time. The variety known as
“Thanksgiving cactus” blooms a few weeks earlier and can be distinguished by
the fact that the last joint on a stem has two prominent teeth. A similar
plant, Easter cactus (Rhipsalidopsis gaertneri), is spring blooming. Plants are
long lived and can grow as tall as 3 feet and at least as wide.
Most cacti prefer full sun, so
give them as much of it as you can. Some will do all right in bright light or
under fluorescent lights. They like warm temperatures during the day but can
tolerate 40 to 45 degrees at night but don’t let them freeze though and may
even bloom better if you turn down your thermostat at night. They like dry air
but will take average humidity. In spring and summer when growth is active they
should be watered thoroughly. However, during the winter they go dormant for a
time, a period they need in order to bloom. They perhaps won’t need water at
all during this time unless they wrinkle. If your water is softened water them
with bottled water, since they cannot tolerate salt.
Moreover, plant cacti in small,
shallow clay pots, with a light, sandy soil except Christmas cacti. Repot in
spring if you see roots in the drainage hole. Don’t feed new plants for a year,
then feed about once a month during the growing season with a weak
concentration of low nitrogen liquid fertilizer; don’t feed cacti at all while
they are dormant. They love to be summered outdoors, in fact the cooler days
and shorter nights at the end of summer can help to trigger bloom, but bring
them indoors when temperatures start to get down into the 40s. Propagate them
by transplanting offsets that have developed their own roots. 
Christmas and Thanksgiving cacti
need more water and fertilizer than other cacti, and they need a more organic
soil. Feed them twice a month in spring and summer, and let the soil dry out a
bit between watering. But starting eight weeks before the time you want them to
bloom, give them a rest. Keep them in a cool place that gets no light at night
50 to 60 degree, give them no fertilizer and just enough water to keep them
from wrinkling, and don’t repot them during this time do it in spring.
Gradually introduce them to warmer temperatures. Water while blooming, and then
keep the cacti on the dry side until spring. They are propagated easily by stem
cuttings.
