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Too Little Water
Most plants do not exhibit dramatic responses to too little water.
Instead, growth slows. The foliage may wilt, and brown leaf tips may
develop. Lower leaves turn yellow and fall off. The surface of the
growing medium shrinks away from the growing container, leading to
deterioration of the fine root system. While most plants prefer a
short dry period in between watering, some require even moisture in
the root zone to survive. Poinsettias, for example, need this to
maintain their green leaves. Color may be lost and leaves may fall
if this requirement is not met.
Too Much Water
As a rule, plants that receive too much water cease forming new
leaves. The most recently formed leaves turn dark green, with the
margins turning tan and cracking. The lower leaves wilt; in time,
they drop or dry slowly on the plant. The stems become dark and
mushy; eventually they rot. The surface of the growing medium
becomes green with algae. All sorts of mosses and ferns may
eventually develop on the surfaces of the growing medium and
container. Watering needs to be monitored closely, as some plants
need less moisture than others.
Too Little Humidity
Fortunately, most green plants thrive even in relatively low
humidity, if watered properly and regularly. When grown with too
little humidity, most plants cease forming leaves. The youngest
leaves become yellow, smaller than normal and crinkly at the edges.
The stems become wiry as the whole plant shrinks in size. The oldest
leaves may dry and drop permanently.
Too Much Humidity
In general, most plants develop new leaves that are covered with
yellow and tan spots. In time, the water-soaked lesions grow larger,
and the centers of the spots rot. In many cases, roots begin to
develop on above-ground stems. Few if any developing flower buds
mature into functioning flowers. The oldest foliage on the plant may
lose its color, collapse and decompose.
Temperatures Too Cool
As a rule, when plants are exposed to temperatures that are too low,
the leaves curl down and around themselves. The most recently formed
leaves may become colorless. Because of reduced nutrient
availability to the slow-growing root system, the old leaves may
turn purple. Raising the temperature, particularly at night, is the
only way to correct the problem.
Temperatures Too Warm
Generally, plants grown with too much warmth do not maintain a
balance between sugars gained from photosynthesis and lost to
respiration. Insufficient sugar slows root development, and water
and nutrient uptake are reduced. Flower production slows, followed
by a rapid loss of the oldest foliage and a paling of the surviving
foliage. Lower temperatures, especially at night, restore growth
and, eventually, flowering.
Liquid Temperatures
Most plants are not sensitive to the temperatures of liquids applied
to their foliage or growing media. Although the temperature of a
liquid may abruptly shift that of the plant tissues, the plant
temperature will rapidly return to the ambient level without any
visible damage. However, some plants are sensitive. A temperature of
68 degrees is optimal for the nutrient solution .Its best to stay
below 74 degrees for prevention of root diseases.
When the temperature of a liquid is 10º F. higher or lower than that
of the leaf, the chlorophyll is permanently damaged. The plant cells
retain their structure, but the leaves are permanently marked with
colorless sections.
Light Excess
In general, too much light causes plant stunting. Even with no
superficial symptoms, internal damage may occur that produces this.
Leaves curl and may appear pale, edged with red. Plants that have
been allowed to dry are susceptible to sunburn. Excessive heat and
light break down chlorophyll, bleaching leaf tissues. Some plants
may suffer leaf discolorations. Pruning damaged leaves, reducing
light and watering properly restore good growth.
Fertilizer Deficit
Most rapidly developing plants quickly deplete the nutrient reserves
available in the growing medium. The first sign of trouble is a
general yellowing of the entire plant. Do not apply only nitrogen;
use a complete water-soluble fertilizer. Plants with too little
fertilizer tend to turn pale green while new top leaves ascend. Few
side branches develop as the oldest leaves turn yellow, dry and
drop. Nutrients from older leaves are transferred by the plant to
newer growth in the plants struggle to survive.
Fertilizer Excess
Excessive fertilizing generally boosts growth initially by favoring
the development of large, deep green foliage. But it produces
problems later. Leaf tips on newer growth begin to brown or burn,
after which older foliage begins to turn yellow, burn and fall
prematurely. Salt damage to the root system renders water
unavailable to the developing roots. These dangers are especially
applicable to peat-based potting mixes and rockwool. Plants may rot
and die rapidly. Reducing fertilizer applications, removing the
upper crust of the growing medium and leaching excess salts corrects
the condition.
pH
The optimum pH for most interior plants is 6.0 to 6.5. In this
slightly acid range, most nutrients are available for uptake by the
roots. Excess fertilizer will cause a dramatic drop in pH, locking
up nutrients before they can be used by the plant. Raise pH in soil
mixes by watering with a suspension of hydrated lime at 2 teaspoons
per gallon of water. Hydroponic solutions can be adjusted with
dilute solutions of phosphoric acid to raise pH and potassium
hydroxide to lower pH. Do not use fish chemicals to adjust pH. Toxic
buildups can occur.
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