extension.missouri.edu > lawn and garden > flowers and houseplants > g6515
LAWN
AND GARDEN
■ ,VVXHG LQ IXUWKHUDQFH RI WKH &RRSHUDWLYH ([WHQVLRQ :RUN$FWV RI 0D\ DQG
-XQH LQ FRRSHUDWLRQ ZLWK WKH 8QLWHG 6WDWHV 'HSDUWPHQW RI$JULFXOWXUH
'LUHFWRU&RRSHUDWLYH([WHQVLRQ8QLYHUVLW\RI0LVVRXUL&ROXPELD02
■DQHTXDORSSRUWXQLW\$'$LQVWLWXWLRQ■■H[WHQVLRQPLVVRXULHGX
Lighting Indoor Houseplants
H
ouseplants are popular indoor decorations.
Attractive and constantly changing, they add a
softness of line and provide a bit of nature indoors.
However, the ideal location of a plant for decoration may
not be the ideal spot for plant growth. Lack of adequate
light is the most common factor limiting the growth of
plants in many areas of the home. Supplementary electric
lighting is usually the easiest and least expensive way to
provide enough light for plants that do not receive adequate
natural light (Figure 1).
Why do plants need light?
Light provides the energy plants need to make the food
required for them to grow and ower. Plants are the only
organisms able to use the energy from light to produce
sugars, starches and other substances needed by them as
well as by other living organisms.
Is light color important to plants?
Certain colors or wavelengths of light are more
important for plant growth than others. Leaves reect and
derive little energy from the yellow and green wavelengths
of the visible spectrum. In contrast, the red and blue
wavelengths of the light spectrum are the most important
energy sources for plants.
Plants growing outdoors, in greenhouses or close to
windows are exposed to a balance of wavelengths of light
from the sun, including the blue and red light that plants
need. In settings where plants receive little or no natural
light, additional light from articial sources must be
provided for adequate plant growth.
What types of artificial lights
are available?
There are four primary sources of articial light available
for the enhancement of plant growth: incandescent;
uorescent; high-intensity, or gas, discharge; and light-
emitting diodes.
As a single light source for plants, incandescent lights are
not particularly good. They are a rich source of red light but
a poor source of blue. Additionally, they produce too much
heat for most plants and, if used, must be located some
distance from the plants, thus reducing the intensity of the
light the plants receive. Important from an economic point
of view, incandescent sources are inefcient in converting
electrical energy into light energy. Furthermore, a standard
incandescent bulb’s life is often only about 1,000 hours,
whereas a uorescent tube’s life is normally 10,000 hours or
more.
Fluorescent tubes provide one of the best articial light
sources available for plants in the home. They are about 2
1
⁄2
times more efcient in converting electrical energy into
light energy than are incandescent sources, making them
less expensive to operate. Additionally, uorescent tubes
produce relatively little heat and are available in types that
emit primarily red and blue light. As mentioned above,
uorescent tubes are relatively long-lived. They are also
available in many sizes and shapes, though straight tubes in
2-, 4- or 8-foot lengths are used most frequently.
High-intensity, or gas, discharge (HID) lights, such
as sodium-vapor or metal halide, are frequently used in
greenhouses when supplementary light is needed. They
are about 10 times more efcient in converting electrical
energy into light energy than incandescent sources.
Revised by
David H. Trinklein, Horticulture State Specialist, Division of Plant
Sciences
Figure 1. Artificial lighting, if properly designed, allows plants to be grown
indoors in nearly any setting.
g6515 University of Missouri Extensionpage 2
Additionally, their bulbs are very long-lived. However, they
emit a lot of heat and the xtures needed to operate them
are large, bulky and relatively expensive. These drawbacks,
along with their lack of availability in small wattages, make
them questionable for use in the home.
Light-emitting diodes (LEDs) represent the newest
source of supplemental light for plants. They are extremely
energy-efcient and very long-lived. LED lights can be
customized to produce the wavelengths of light desired. For
example, LED plant lights emit only the red and blue light
needed by plants. They emit very little heat and require no
ballasts or reectors. Currently, however, the price of LED
systems is high when compared with other sources.
What light source is most popular
for interior settings?
Given their modest initial purchase price, energy
efciency and ease-of-use, uorescent lights are the choice
of many indoor gardeners. Although cool-white uorescent
tubes remain the most popular choice, warm-white
uorescent tubes also seem fairly effective. Fluorescent
tubes listed as white or daylight are less desirable for indoor
plant growth. Cool-white tubes produce a small amount
of red rays — in addition to orange, yellow-green and blue
rays — but usually not enough for plants unless windows or
other articial lights provide additional red rays.
A few incandescent bulbs in the growing area can
furnish needed red rays. A general ratio of incandescent
to uorescent light is about 3 to 10, so for every 100 watts
of uorescent light, you should provide about 30 watts of
incandescent light for a better red-to-blue light balance.
The uorescent tubes developed specically for growing
plants have a higher output in the red range to balance the
blue output. Many home gardeners have found that these
tubes can be used in combination with cool-white tubes.
Use one plant-growing tube to each one or two cool-white
tubes. This method is more economical than using all
plant-growing tubes, because cool-white tubes cost less
than the plant-growing tubes. Also, the plant-growing tubes
use less electricity and produce less heat than incandescent
bulbs, and you will not have to provide xtures for both
incandescent bulbs and uorescent tubes.
Can I use spotlights?
Spotlights can be used to light indoor houseplants,
though they are not the most effective solution. Most are
incandescent and, thus, are not energy efcient; give off a
lot of heat; and do not produce a good balance of red and
blue light, although self-reectorized spot lamps coated
to emit more blue light are available. Reserve these special
light sources for situations where supplementary light is
essential but other sources cannot be used.
How much light should plants receive?
The amount of light necessary varies with each plant. In
general, the light xtures available for home plant lighting
make it practically impossible to produce too much light for
most plants.
Plants that can adapt to interior settings usually are
divided into three general categories: those suitable for low,
medium and high light intensities. (These three groups
are referred to in the discussion of individual plants in the
last section of this publication.) The categories generally
indicate the minimum light required. Growth is often best
at the higher end of these suggested light ranges.
Foot-candle
A foot-candle is a measure of light intensity, or brightness. It
is defined as the amount of light received by a 1-square-foot
surface that is 1 foot away from a light source equivalent to one
candle of a certain type.
Low-light plants
Plants referred to as low light intensity plants generally
should receive between 50 and 250 foot-candles. Under
articial light, a few plants in this group can be maintained
at as little as 10 foot-candles. Low-light plants should
receive between 10 and 15 watts of uorescent light per
square foot of growing space. A single uorescent tube such
as a 2-foot 20-watt tube or a 4-foot 40-watt tube without
any other light provides only enough light for plants in this
category (Table 1).
Medium-light plants
Medium light intensity plants prefer 250 to 1,000 foot-
candles. Best growth occurs above 750 foot-candles unless
plants also receive extended periods of direct sunlight.
Give them articial light in the 500 to 1,000 foot-candle
range, or 15 or more watts per square foot of growing
area. Although plants in this group can be held in the 250
to 500 foot-candle range, growth is best with more light.
A xture containing two uorescent tubes is sufcient for
Table 1. Light output measured at various distances below
fluorescent lamps
†
.
Distance
(feet)
Light output (foot-candles)
‡
based on fixture type
1
⁄2 500 700 900
1 260 (200) 400 (260) 600
2 110 (100) 180 (150) 330
3 60 (60) 100 (90)
4 40 60 100
† All lamps are standard 40-watt tubes.
‡ Output in parentheses is measured 1 foot on either side of a line directly below
the lamps.
g6515 University of Missouri Extensionpage 3
plants in the low- to medium-light range. Adjustments in
the number of tubes used may be made if you regulate the
distance between the tubes and plants.
High-light plants
Plants that require high light intensity generally are less
satisfactory for growing under articial lights in the home.
However, if you want to try, use special high-intensity
lamps. These plants need at least 1,000 foot-candles, or
20 watts per square foot of growing area, but should have
higher intensities for best growth and owering. Fixtures
containing three to four uorescent tubes are necessary for
plants requiring high light intensity.
How far from the light should I
place plants?
Most plants should be located with the tips of the plants
6 to 12 inches from the light source. The intensity of light
drops rapidly as the distance from the light bulbs or tubes
increases. Table 1 shows this reduction of light intensity
with distance below and to the side of tubes. Fluorescent
tubes do not produce as much light at the ends as they do in
the center, so the brightest spot under a uorescent xture
is directly beneath the center of the tubes.
The light xture’s position should be adjustable so you
can keep the distance between the light and the plant fairly
constant. Fluorescent shop or workroom xtures often are
hung on chains with S-hooks for easy adjustment. These
xtures are easily raised or lowered from link to link. If the
xture is not movable, you may make some adjustment by
raising plants on stands, shelves or boxes.
How long should I use lights?
In most cases, plants receiving no outdoor light should be
lit from 16 to 18 hours each day. If some additional light is
received, 12 to 14 hours each day may be adequate. Lights
should be used at the same time that plants receive window
light. Using lights at the beginning or end of the day will
not usually be as effective as using lights during daylight
unless natural daylight is quite bright.
How can I get the most
from artificial light?
Reectors and reective surfaces can maximize the
available light. Bulbs with self-contained reectors are
helpful.
Porcelain-coated reectors are excellent and require
little maintenance. Keep reectors clean and free of rust or
any coating that reduces their effectiveness. White paint or
aluminum foil beneath or around the growing area helps
reect light and makes it more efcient.
Space plants far enough apart to allow light between
them. Arrange plants so they do not shade each other. Keep
tubes clean and replace old tubes promptly.
How should I light the bottom
of a tall plant?
You may want to supplement light placed above a tall
plant with spotlights around the base of the plant and
directed on the lower leaves. You can also use uorescent
tubes in a vertical position to provide side lighting from the
top to the bottom of a plant. This vertical position also can
be used for smaller plants arranged on shelves (Figures 2
and 3).
Do I really need to measure light?
Light measurements are helpful in setting up a plant
growing area but should be used only as a guide. The
human eye is a poor judge of light intensity because
it automatically adjusts to different light levels. Light
meters that measure foot-candles may be used if available.
Photographic light meters normally do not read in foot-
candles, but some manufacturers supply a conversion table.
When available, these may also be used.
Calculating wattage per square foot of growing area is a
useful and easy way to estimate light required. When using
uorescent tubes, simply multiply the wattage desired
by the square feet of growing area. For example, if you
have a 4-square-foot area of low-light plants that need 10
watts, the calculation would be 10 watts × 4 square feet,
or 40 watts. With this approach, light measurements are
unnecessary unless problems develop.
Figure 2. This homemade vertical lighting system with adjustable shelves
can accommodate small or large plants.
6'
24"
24"
Light
fixture
panel
6" shelves
Timer
3/4"
plywood
Detail of
light fixture panel
g6515 University of Missouri Extensionpage 4
How can I tell if a plant is getting
enough light?
The growth pattern of the plant can be a good indication
of whether it is getting enough light. No growth may
indicate poor light but could be a sign of other problems as
well. The signs that a healthy plant is not getting enough
light include development of long internodes (length of
stem between leaves) or of smaller-than-normal leaves; pale
green stems and foliage; and lower leaves that are yellow
and dropping.
What window provides the best light?
When choosing windows to place plants near, consider
size, direction, overhang and shade from trees or buildings.
Large windows provide the best growing conditions and
allow plants to be placed fairly far back into a room. But
even low-light plants usually do not receive enough light
at distances greater than 10 feet from an average window.
The best windows for plants are those not shaded by a large
overhang, trees or structures.
Windows facing south provide the brightest light
conditions for the longest duration. In winter, any
houseplant benets from the light of a south window.
However, plants that do not need bright light may be
sunburned by the bright light at south windows in late
spring, summer or early fall. Place plants requiring less
light, such as African violets, at a north window or to the
side or interior of a large south window during these times.
South windows are most appropriate for plants requiring
bright light and some direct sunlight.
East and west windows are well suited to many plants
in the medium light range, whereas north windows are
satisfactory only for plants requiring the lower light levels.
These plants should not receive direct sunlight.
Can lights keep plants from blooming?
Some plants, generally known as short-day plants, can
be kept from owering under the light durations normally
used for articial lighting. Best known in this category are
the poinsettia and chrysanthemum. To induce owering
indoors, give these plants only about 10 hours of light each
day until owers become visible and color shows.
Will artificial lights start seeds?
Vegetable, annual ower and some perennial ower seeds
may be started successfully indoors under lights for later
planting in the garden. For stocky growth, place seedlings
within a few inches of the tubes as soon as germination
begins.
Is a light timer necessary?
A timer is a valuable asset because lights should be turned
on and off regularly and consistently. Twenty-four-hour
timers available from electrical supply houses are adequate.
The electrical cord from the timer should be the three-
prong type, or you should use a grounded adapter. The use
of water around plants makes grounding electrical xtures
important.
Figure 3. Small, low-light plants (such as African violets) are well suited for
light gardens.
Plants for indoor lighting
African violet, Saintpaulia species. This is one of the
most satisfactory owering plants for growing under lights;
it grows and owers well between 500 and 1,000 foot-
candles. Light 16 to 18 hours each day.
Aluminum plant, Pilea cadierei. This small plant with
colorful leaves tolerates a low light level but needs high
humidity. Other suitable related plants include artillery fern
and moon valley pilea.
Arrowhead vine, Syngonium podophyllum. These small
plants are bushy and later, creeping or climbing. They may
be kept at a low light level, but they are denser at a medium
level.
Asparagus ferns, Asparagus densiorus ‘Sprengeri’ and
Asparagus setaceus (formerly plumosus). These durable potted
plants with eshy roots produce fernlike leaves. Although
tolerant of low light, the plants grow more abundantly and
densely in a medium light range.
Aucuba-leaf croton, Codiaeum ‘Aucubaefolium.’
Crotons are not appropriate as indoor plants because they
require high light for good color development and growth.
g6515 University of Missouri Extensionpage 5
However, this smaller
type with yellow
spots can be grown
at medium light
intensities.
Begonias:
Angelwing, Begonia
coccinea; Beefsteak,
B. xerythrophylla;
Iron cross, B.
masoniana; Flowering,
B. semperorens;
and Painted B. rex
varieties. Most plants
of this family are
suitable for growing
in the medium light
range. Begonias like
high humidity and
constantly moist soil.
Give them a long light duration, from 14 to 18 hours each
day.
Cacti and succulents. Many plants may be grouped
in this general category. These plants need high light
intensities; most are not satisfactory for growing under
articial lights. However, you can use lights to maintain
them for limited periods when they cannot be exposed to
bright light or direct sunlight. When articial lights are
used, provide high intensities, and keep plants close to the
source.
Cast iron plant, Aspidistra elatior. This plant tolerates
cool locations and poor light; it is one of the best plants
where only low light conditions exist. A variegated form is
also available.
Chinese evergreen, Aglaonema modestum. Aglaonemas
are relatively small tropical plants but can tolerate light as
low as 10 foot-candles. Other species with different leaf
form and variegation are also available.
Cissus species: Grape ivy, Cissus rhombifolia; and
Kangaroo vine, Cissus antarctica. Cissus are climbing plants
that prefer medium light conditions for best growth,
although kangaroo vine tolerates lower light. Although
better for greenhouse culture, another beautiful relative is
the rex begonia vine, Cissus discolor.
Dieffenbachia, Dieffenbachia maculata. Many satisfactory
species and varieties are available. Plants have large, showy
leaves with spotting and variegation. Medium light range is
best and will prevent loss of lower leaves. Overly tall plants
can be cut back. Dieffenbachia benets from supplementary
lighting in poorly lit areas.
Dracaena species: Corn plant, Dracaena fragrans
massangeana; Dragon tree, Dracaena marginata; Janet Craig
dracaena, Dracaena deremensis ‘Janet Craig’; and Ti plant,
Cordyline terminalis ‘Ti.’ Most dracaenas become large
plants. They are well adapted to house conditions and
tolerate low light although they also do well in medium
light. They need to be kept warm and constantly moist for
best growth. Ti plant develops best leaf color in bright light
and therefore is less
suitable for locations
where it receives only
articial light.
Ferns: Birdsnest
fern, Asplenium
nidus; Boston fern,
Nephrolepis exalta
bostoniensis; Holly
fern, Cyrtomium
falcatum; and Maidenhair fern, Adiantum species. The
word “fern” brings to mind the Boston, or sword, fern with
its many varieties. These ferns are durable houseplants
that tolerate low light but prefer a medium light level.
Keep them cool and moist. Holly fern likes cooler house
temperatures; however, birdsnest fern prefers warmer
temperatures. Ferns may develop brown leaves or leaets at
low humidity. Maidenhair ferns should never be allowed to
become dry.
Ficus species: Rubber plant, Ficus elastica varieties;
ddleleaf g, Ficus lyrata; and weeping g, Ficus benjamina.
These large plants are well suited to most home conditions
and are best grown in a medium light range. Low light may
result in a drop of foliage. Keep soil evenly moist. They
tolerate low humidity.
Flame violet, Episcia cupreata varieties. These close
relatives of the African violet have beautiful foliage in many
color patterns. Flowers are red, pink, purple and yellow.
Light needs are the same as for African violets. The plants
need high humidity and temperatures that do not drop
below 65 degrees F.
Gloxinia, Sinningia speciosa fyana varieties. This
colorful African violet relative needs a medium light range
to prevent elongation of the stems as well as to promote
abundant owering. Buds sometimes appear but fail to
develop, which may indicate insufcient light, too low
humidity or mite damage.
Herbs: Culinary herbs can be grown indoors, but for
best growth, most of these require fairly bright light. If you
attempt them under articial light, use as much light as
possible with a long duration.
Hoya: Hindu rope plant, Hoya carnosa ‘Hummels
compacta’; and wax plant, Hoya carnosa. Hoyas are vining
plants with thick, waxy leaves. They tolerate low light but
need medium light to grow and high light to ower. Plants
should not be moved; allow them to remain undisturbed.
Keep slightly cooler and drier in winter.
Ivy, Hedera helix varieties. These vining plants with
leathery leaves grow best in medium to bright light areas.
They need constant moisture to prevent leaf drop, and they
tend to grow better when kept slightly cool indoors.
Jade plant, Crassula argentea. This succulent plant is well
adapted to indoor conditions. Although most crassulas
prefer sun, jade plant will tolerate lighting as low as 25
foot-candles; however, growth will be thin and leaves small.
Avoid overwatering and tight soils.
Little-leaf schefera, Schefera arboricola. This medium-
sized plant has waxy leaves that are made up of leaets that
Figure 5. Gold dust dracaena.
Figure 4. Dieffenbachia benefits from
supplementary lighting in poorly lit areas.
page 6g6515 New 3/78; Revised 06/16/1M
begin at a shared
point near the based
of the leaf and radiate
outward much like
ngers from the palm
of an open hand. It
has a bushy type of
growth and, although
it prefers higher
amounts of light, it
will tolerate medium
light quite well.
Norfolk Island
pine, Araucaria
heterophylla (formerly
excelsa). This is a durable plant for home conditions.
Although tolerant of poor light, it develops better growth
in medium light conditions. With poor care and low light, it
may lose symmetry.
Orange: Dwarf or calamondin, Citrus mitis. Potted citrus
plants prefer bright light for best growth and fruiting.
You may keep them at medium light intensities during
midwinter. The calamondin orange is the most popular
potted citrus, although Meyer lemon and Ponderosa lemon
are also satisfactory for home use.
Orchids: Few orchid species are well suited to the
average home’s articial light conditions. Seedling plants
do well under articial lights; however, mature plants need
bright light for best growth and owering. Some genera
better adapted to the light garden include Epidendrum,
Paphiopedilum, Brassavola and Phalaenopsis. All orchids need
excellent drainage and air movement.
Palms: Areca palm, Crysalidocarpus lutenscens; Dwarf date
palm, Phoenix roebelenii; Neanthe bella palm, Chamaedorea
elegans ‘Bella’; Bamboo palm, Chamaedorea erumpens; and
Kentia palm, Howeia forsteriana. Neanthe bella and kentia
palms are most tolerant of low light conditions. Other
palms are best suited to medium light areas. Bright light
may cause fading in some species. Palms prefer fairly
uniform moisture, but occasional slight drying can be
benecial. Palms grow relatively slowly indoors. Keep close
watch for spider mite damage.
Peperomias: Baby rubber plant, Peperomia obtusifolia;
Emerald ripple, Peperomia caperata; and many other suitable
species. Most peperomias have eshy leaves and stems.
They are small plants well adapted to home conditions.
Provide a medium light level, although peperomias can
tolerate poor light for limited periods. Avoid overwatering,
which may promote stem rots.
Philodendrons: Heartleaf philodendron, Philodendron
oxycardium; Splitleaf philodendron, Philodendron pertusum;
and other suitable species. The heartleaf philodendron
tolerates low light; most prefer a medium light range for
best growth indoors.
Most are well adapted
to home growing.
They should be
maintained at fairly
uniform moisture.
Pilea species:
These small but
colorful plants
(for example, Pilea
caperata, Emerald
ripple pilea) are
excellent choices
for table tops,
dish gardens and
terrariums. They require the same light conditions as do the
peperomias.
Pleomeles: Lance dracaena, Pleomele reexa; and
Malaysian dracaena, Pleomele thaliodes. These plants are
gaining popularity because of their durability as potted
plants and tolerance to low light conditions. They grow best
in a medium light range with uniform soil moisture.
Pothos, devil’s ivy, Epipremnum aureus. This
popular variegated climbing vine is similar to heartleaf
philodendron and satisfactory for low and medium
light conditions. It requires less uniform moisture than
philodendron.
Sansevieria, snake plant, mother-in-law-tongue,
Sansevieria trifasciata. This very popular and durable plant
grows well indoors. It tolerates poor light but makes best
growth in medium to bright light conditions. Dwarf and
variegated forms are available. Avoid overwatering.
Schefera, umbrella tree, Brassaia actinophylla. This
plant prefers bright light but tolerates medium light or even
low light for limited periods. It will drop foliage in extended
periods of poor light or if kept too wet or too cool. Spider
mites are a common problem.
Spathiphyllum, peace lily, Spathiphyllum species, for
example, ‘Supreme’ or ‘Sensation.’ These plants adapt to
low light conditions but need medium light to ower. Their
white, anthurium-like owers are long-lasting. Do not
allow plants to dry out.
Spider plant, airplane plant, Chlorophytum comosum
‘Vittatum.’ Long drooping leaves and runners producing
small plants make this a popular hanging plant. Solid green
and variegated types are available. They tolerate low light
but grow best in the medium range. Keep well watered.
Swedish ivy, Plectranthus australis. This creeping plant is
used for hanging containers. Although it tolerates low light,
more dense growth and branching occur at medium light
intensities.
Original author: Ray R. Rothenberger
Figure 6. Oval-leaf peperomia. Figure 7. Moon valley pilea.
