Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001596
11/12/99
Watering House Plants
Of all the things done to house plants, watering is
probably the one cultural practice that causes the most
problems. Watering is affected by the type of soil used,
light exposure, temperature, and humidity. Many factors
determine when a plant needs to be watered. Just as many
environmental factors change with the seasons, so do the
water needs of plants.
The two main aspects of watering to be considered are
frequency of watering and amount of water applied. The
watering frequency is simply how much time passes between
watering. The frequency will vary over the course of the
year. Avoid watering on a fixed schedule such as every
week or every 5 days. A fixed schedule does not
necessarily give plants water when they need it. In fact,
watering on a fixed schedule may mean plants are over-
watered at one time of the year but under-watered at
others. With few exceptions, plants should be watered
when the soil feels dry to the touch. This means the
frequency of watering will vary with the rate at which the
soil dries out.
Apply enough water so some comes out the drainhole at
the bottom of the pot. This flushes out salts which can
lead to root injury. Do not let plants sit in excess
water. It will be re-absorbed and the salts dissolved in
the water will be re-absorbed. There is no easy way to
tell when plants in undrained containers have had enough
water.
The actual technique for watering is not difficult. The
best way is to use a watering can with a long, narrow,
spout. This allows the placement of water on to the soil.
Watering plants with dense foliage will be more difficult
if this type of watering can is not used. Try not to put
the water on the leaves and crown. Occurrence of rot
diseases is more likely if water is continually poured on
the crown.
The water should not be very warm or very cold. Tepid
water, or water near room temperature will probably be
best.
Bottom watering is a practice where the plant is set in
and absorbs water from a container filled with water.
Plants regularly watered from the bottom should
occasionally be watered from the top to get rid of excess
salts in the soil. The bottom layer of soil becomes
saturated when a plant continuously sits in water. Any
roots growing in this saturated layer will die. The soil
available for plant growth is thus reduced.
Some plants enter rest periods at some time of the year.
Resting plants may use less water so are more likely to be
over-watered. If a plant slows or stops growing in late
fall or early winter, it may be entering a rest period.
At the same time the furnace may start running and dry the
air out, causing the soil to dry out more quickly.
Concern about over-watering resting plants in winter must
be tempered by consideration of the effect of lower house
humidity.
Terms such as constantly moist, allow to dry between
watering, and moderately moist are often used. These
terms can be confusing. They are not precise and can be
interpreted in ways which result in plant injury. Few
plants are able to grow in constantly soggy soil. Few
plants can last long in soil which has dried out
completely. Between these two extremes is plenty of room
for watering mistakes. If cultural instructions say, the
soil should be constantly moist, or the plant likes
moisture, watch the soil closely. When the soil surface
has barely begun to dry, water the plant. The plant able
to grow, sitting in a constant supply of water, is the
exception not the rule. If cultural instructions say,
the plant likes to dry between watering, the soil
surface should dry before the plant is watered. At no
time should all of the soil in the pot become dry. Use
watering terms as guides, not rules, as to how a plant
should be watered.
Plants intolerant of a lot of moisture can be grown in
well-drained soil mixes. Plants requiring more soil
moisture can be grown in soil mixes which hold more
moisture.
Soil moisture meters can be used as a guide to determine
when a plant needs water. These meters can be
useful but can't replace knowledge about plant needs. The
meters can give false readings in soils with excess salts.
The readings may vary depending on how deep the probe is
inserted into the soil. Spend time with the meter, using
different readings and different probe depths, to
determine which readings give best plant growth.
The main symptom of watering problems is wilting. Plant
wilts if given too much or too little water. The only way
to tell the difference is to check the soil. If it feels
wet or soggy, the plant has been over-watered. Plants
consistently over-watered often develop stem or root rots
which causes the lower leaves to yellow and drop.
Water from a home water softener, used for a long period
of time, will kill plants. This type of water softener
often uses rock salt. The most common symptom is browning
of the leaf margins.
This information is for educational purposes only. References
to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
publication and may be printed verbatim with credit to MSU
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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