of Rhode Island GreenShare Factsheets
the Home Garden
Adequate soil moisture is essential for good crop growth.
A healthy plant is composed of 75 to 90% water, which is used
for the plant's vital functions, including photosynthesis,
support (rigidity), and transportation of nutrients and sugars
to various parts of the plant. During the first few weeks of
growth, as plants are becoming established, they must have
water to build their root systems.
While growing, vegetable crops need about 1 to 2 inches
of water per week in the form of rainwater or irrigation water,
depending on the type of soil. One thorough watering each week
is usually enough for most soils. The soil should be wetted
to a depth of 5 to 6 inches each time you water and not watered
again until the top few inches begin to dry out. An average
garden soil will store 2 to 4 inches of water per foot of depth.
Keep a rain gauge near your garden and supplement rainfall
with irrigation water if needed.
All of the water added to the garden may not be available
to plants, particularly if the soil is a heavy clay (although
this is rare in Rhode Island). Clay particles hold soil moisture
tightly; if, for example, there are 4 1/2 inches of water per
foot of this type of soil, there may be as little as 1 1/2
inches of this water available for plants. A higher level of
humus in the soil, brought about by the addition and breakdown
of organic matter, can increase the amount of water available.
By causing clay particles to aggregate (stick together), humus
also adds air spaces to tight clays, allowing moisture to drain
to lower levels as a reserve instead of puddling and running
off the top of the soil.
The moisture-holding capacity of sandy soils is also improved
by additions of organic matter. Though most soil water in sandy
soil is available to plants, it drains so quickly that roots
are unable to reach water only a few days after a rain. Humus
in sandy soil gives the water something to cling to until it
is needed by plants. Addition of organic matter is the first
step in improving the moisture conditions in your garden.
Mulching is another a cultural practice which can significantly
decrease the amount of water that must be added to the soil.
An organic mulch six to eight inches deep can cut water needs
in half by smothering weeds (which take up and transpire moisture)
and by reducing evaporation of moisture directly from the soil.
Organic mulches themselves hold some water and increase the
humidity level around the plant. Black plastic mulch also conserves
moisture but may dramatically increase soil temperatures during
the summer if not covered by other mulch materials or foliage.
See GreenShare Factsheet on mulch for
more information and recommendations.
Shading and the use of windbreaks are other moisture-conserving
techniques. Plants that wilt in very sunny areas can benefit
from partial shade during the afternoon in summer. Young plants
need particular protection. Air movement across a plant carries
away the moisture on the leaf surfaces, causing the plant to
need more water. In very windy areas, the roots often cannot
keep up with leaf demands, causing wilt. Temporary or permanent
windbreaks significantly reduce this stress.
Even with the implementation of all of these cultural
practices, a garden may still need a substantial amount of
water. When rainfall is sparse and the sun is hot, watering
can benefit your garden with increased yields. It may save
the garden altogether in a severe drought. Irrigation practices,
when properly used, can:
* Aid in seed emergence
* Reduce soil crusting
* Improve germination and plant stand
* Reduce wilting of transplants
* Increase fruit size of tomatoes, cucumbers, and melons
* Prevent premature ripening of peas, beans, and sweet corn
* Maintain uniform growth
* Improve the quality and yields of most crops
The home gardener has several options for applying water
to plants, including a sprinkler can, a garden hose with a
fan nozzle or spray attachment, a portable lawn sprinkler,
a perforated, plastic soaker hose, a drip/trickle irrigation
system or a semi-automatic drip system. Quality equipment will
last for a number of years when properly cared for. When making
a decision as to which type of watering equipment you will
use, there are a number of things to consider.
The purchase of a specific type of watering equipment
depends upon available water facilities, water supply, climate
and garden practices. If there is no outdoor spigot near the
garden, the expense of having one installed may be greater
than the benefits gained, except in very drought-prone areas
or in the case of a gardener who is fully dependent on the
season's produce. Where rainfall is adequate except for a few
periods in the summer, it is wise to keep watering equipment
simple. A rain barrel or a garden hose with a fan-type sprinkler
may suffice; a water breaker for small seedlings is useful.
In areas where there are extended periods of hot weather without
precipitation, the local water supply is likely to be short.
Since overhead sprinklers waste water, a drip irrigation system
may be in order. Drip irrigation provides water to roots without
wetting plant leaves, helping to control some diseases. Timers
are available that allow automatic watering with drip irrigation
Several types of drip or trickle equipment are available.
The soaker hose is probably the easiest to use, as it requires
no installation. A soaker hose is a fibrous hose that allows
water to slowly seep out all along its length. It is simply
laid at the base of the plants and moved around the garden
as needed. There are also complete kits containing attachments
and PVC hose with holes to allow gradual water release. These
are intended for semi-permanent installation and usually last
2 to 5 years. With this type, a flow regulator usually has
to be included with the system so that the water can reach
the end of the hose without being sprayed out at full force.
A special double-walled type of irrigation hose has been developed
which helps to maintain a more even flow. Finally, there is
the emitter-type system, best used for small raised beds or
container gardens, in which short tubes, or emitters, come
off a main water supply hose and go right to the roots of the
individual plants. This is generally the most expensive form
of irrigation and the most complex to set up, but it has advantages.
The weeds in the area are not watered and evaporation from
the soil is minimized. This type of system is best used in
combination with a coarse mulch or black plastic. Drip systems
can have problems with clogging from soil particles and/or
mineral salts suspended in water taken from springs or wells.
New designs take this problem into consideration; some include
filters and self-flushing emitters. It is wise to make a complete
investigation and comparison before purchasing a drip irrigation
For overhead or sprinkler watering, adjust the rate of
water application to about 1/2 inch per hour. A faster rate
will cause run-off unless your soil has exceptionally good
drainage. To determine the rate for a sprinkler, place small
cans at various places within the sprinkler's reach and check
the level of water in the cans at 15-minute intervals. When
using the oscillating type of lawn sprinkler, place the sprinkler
on a platform higher than the crop (to prevent water from being
diverted by plant leaves), and try to keep the watering pattern
even by frequently moving the sprinkler and overlapping about
half of each pattern.
Do not use sprinkle irrigation in the evening, as foliage
that remains wet overnight can encourage diseases. Morning
watering is preferable, as there will be less water lost to
evaporation than during the heat of the day. Add enough water
to soak the soil to a depth of 5 to 6 inches--the precise amount
required varies with the nature of your soil. Frequent, light
waterings will encourage shallow rooting, causing plants to
suffer more during drought periods, especially if mulches are
not used. On the other hand, too much water, especially in
poorly drained soils, can be as damaging to plant growth as
too little water, depriving the roots of oxygen needed to grow.
By knowing the critical watering periods for selected
vegetables or vegetable types, you can reduce the amount of
supplemental water you add. This can be important, especially
where water supplies are limited. In general, water is most
* during the first few weeks of development
* immediately after transplant
* during development of fruits
The critical watering periods for some specific vegetables
Asparagus -- Spear production, fern development
Broccoli, Cabbage, Cauliflower -- Head development
Beans, peas -- Pod filling
Carrot -- Seed emergence, root development
Corn -- Silking, tasseling, ear development
Cucumber, Melon --Flowering, fruit development
Eggplant, Tomato --Flowering, fruiting
Lettuce -- Head development; moisture should be constant
In areas prone to repeated drought, look for drought-resistant
varieties when buying seed or plants.
If water supplies are short in
your area and you wish to use "gray water" (water from household
uses) on your vegetable garden, a few rules should be observed:
* Do not use any water run through the toilet, because of the possibility of
contamination from fecal organisms.
* Avoid the use of kitchen waste water that contains grease or harsh cleaners,
ammonia, bleach, softeners or non-biodegradable detergents.
* If using water from the bathtub or washing machine, use only mild, biodegradable
soaps. Omit softeners and bleaches. Allow the wash and rinse water to mix,
if possible, to dilute the soap content. Never use a borax-containing product
(such as washing soda) in water to be used on a garden because of the danger
of applying levels of boron toxic to plants.
* Apply gray water to the soil, not to plant leaves.
Adapted from Diane Relf,
Virginia Cooperative Extension, 2000
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
of Rhode Island Cooperative Extension provides equal program