“A”
horizon |
- this is the top layer of soil that
contains both mineral elements and organic matter.
It is usually darker colored than other horizons and is
often called top soil. Plants grow primarily in the
topsoil.
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abiotic (plant problems) |
- the term applies to any
non-living cause for a plant problem.
Animals,
insects,
spider mites, fungi,
bacteria, etc. would be considered
biotic
causes of plant damage. Nutrient deficiency, physical
damage, weather impacts, poor drainage and other
non-living factors would be called abiotic causes of
plant problems. More... |
abscise |
-
(n. abscission) One of the mechanisms that plants have
developed in order to survive cold or extremely dry
periods is to drop their leaves. These tender tissues
will then die and be replace when better weather appears
again.
Deciduous
trees form a zone between the stem and the base
of the leaf stalk (petiole) called the
abscission layer.
This is encouraged by the production of a hormone called
abscisic acid.
Once the layer is complete, it severs the connection
with the tree and the leaf drops to the ground without
leaving a open wound. |
abscisic acid |
- this plant hormone is
involved in
bud
dormancy, seed dormancy and
helps regulate the opening and closing of
stomata on leaves. It is also
vital to the formation of the abscission zone at the
base of leaves in the autumn which allows them to fall
off without the loss of sap through the resulting wound. |
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abscission
zone |
- in
autumn, deciduous plants form a
layer of cells at the base of a leaf petiole, flower or
fruit stalk in response to a build up of
abscisic acid. This layer
forms a weakening of the tissue which causes the
organ to separate from the plant and fall off.
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absorption |
- when
water is taken into the soil or into the root of the
plant, it is absorbed.
Compare with adsorption. |
acaricide |
-
aka
miticide - any chemical or material capable of killing
spider mites. Remember
that spider mites are NOT
insects since they have 8 legs
and not 6. Therefore, not all insecticides will affect
them. |
accent plant |
- in the landscape,
this is a plant used to call attention to a
particular feature of an area, for example, an
attractive shrub planted near the front door of a house. |
acclimatization |
- (aka acclimation) the process
of plants adapting to some element of the climate or environment,
such as to winter cold or summer heat. The gradual
preparation of seedlings before being introduced to a change in environment from a protected place such as a greenhouse
or basement. It helps them to adjust from optimum
growing conditions to potentially cruel weather
outdoors. See hardening
off. |
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achene |
-
small, dry, indehiscent,
one-seeded fruit with a tight, thin outer wall.
Examples: sunflower and buttercups. Achenes with wings
are called samara which are
found on
maples
(Acer). |
acid-forming |
-
a material that helps to acidify the soil or
acidifies the soil
as it decomposes.
For example,
peat moss, garden sulfur,
and
oak leaves. Some
fertilizers such as Urea or
ammonium sulfate also help to make the soil more acid. |
acid rain |
-
precipitation containing certain acids and
acid-forming substances and falling on soils, plants,
and open waters. This is generally produced by
industrial discharges into the air. Pollution control
devices added to smoke stacks has helped to reduce (but
not eliminate) this problem. |
acid or acid soil |
-
for gardeners, acid is defined as any substance which
has a
pH lower than 7.0 (which is
neutral). Most landscape plants grow best with a
slightly acid soil with a pH in the range of 6.0 to 7.0
although a few species
require a even lower pH (more acid) soil for proper
growth. There are a handful of plants that prefer an
alkaline soil above 7.0. The pH of the soil is
important in that it regulates the intake of nutrients
into the plant. If the pH is in the wrong range for a
particular species, it may show nutrient deficiencies
even though there is plenty of that nutrient in the soil
nearby. |
active
ingredient |
- the component of a
pesticide product that actually kills the pest. Active ingredients
(a.i.) are normally mixed with
inert or inactive ingredients in the formulation
process. The percentage of active
ingredient in a pesticide must be listed on the label.
For example in the very common herbicide, RoundUp, the active
ingredient is glyphosate. |
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actual nutrient (as in actual nitrogen). |
-
the portion or percentage of a
fertilizer that supplies
nitrogen.
All fertilizer containers must by law list the
percentage of N (nitrogen
as elemental nitrogen - N),
P (phosphorus in the form
of phosphate - P2O5) and K (potassium
in the form of potash - K2O).
A 100
pound bag of 27-10-15 fertilizer would contain 27 pounds
of nitrogen, 10 pounds of phosphate and 15 pounds of potassium. |
acuminate |
-
usually referring to a leaf that has a
pointed tip or one that is tapering to a point |
acute toxicity |
-
an impact that occurs quickly after an exposure. If
someone spraying a
pesticide does not use the proper
protective equipment and then becomes ill immediately
after spraying, that would be acute toxicity.
See
chronic toxicity. |
Aden, Paul |
Early hosta hybridizer and author of The Hosta
Book, published in 1988 by Timber Press in 1988 (ISBN 0-88192-087-8) |
adjuvant |
- an ingredient that improves the properties of
a
pesticide formulation. Includes
wetting agents,
sticker/spreaders, emulsifiers, dispersing agents, foam
suppressants, penetrants, and correctives which tend to make the
pesticide more effective. |
adsorption |
- the
binding of a chemical to surfaces of mineral or soil
particles. Often
nutrients in the soil are adsorbed to
soil particles and then are available to nearby plant
roots. Compare with absorption. |
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adventitious |
-
referring to a plant structure arising from an unusual place,
such as buds
at other places than leaf axils or roots
growing from stems or leaves. Sometimes these may be
thought of as "buds in waiting" which may not become
active until the plant needs them. |
aeration |
- it is the process of opening up the soil to mix in more
air such as core
aeration in lawns or
double digging of flower beds. Soils need to have
about 25% of their volume in air/oxygen for healthy root
growth on most plants. When the air has been squeezed
out of the soil, it is called compaction. |
air
layering |
- a
means of asexual propagation that involves rooting the
stem of a plant without completely detaching it from its
original root system. Certain shrubs and vines may be
propagated this way. Normally, a small branch is cut
just through the bark but left attached to the mother
plant. A rooting compound is applied to the wound. Then,
the entire stem around the wound is encased in wet
sphagnum moss covered by aluminum foil or plastic wrap.
Over time, new roots develop at the wound. The stem may
then be cut below the roots and the resulting rooted
cutting may be planted on its own. |
air prune |
-
this term applies to the practice of allowing the roots
of plants to grow out the drainage holes in pots. Then,
they are allowed to dry out and the roots exposed to the
air will die back. |
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albescent |
-
or albescence -
Some hosta leaves change color as the summer season progresses.
Leaves that start out yellow or green in the spring and slowly
turn white as the season progresses are called albescent. Here
is a
list of albescent hostas. |
alkaline soil |
-
soil with an alkaline or basic reaction and has a
pH higher than 7.0 (which
is neutral). Most landscape plants grow best with a
slightly acid soil with a pH in the range of 6.0 to 7.0.
Only a few prefer a soil with an alkaline pH. The pH
of the soil is important in that it regulates the intake
of nutrients into the plant. If the pH is in the wrong
range for a particular species, it may show nutrient
deficiencies even though there is plenty of that
nutrient in the soil nearby. |
allelopathy |
-
some plants have developed the ability to excrete a
substance from their roots that is poisonous to other
plants. This helps them to compete favorable in the
environment. Perhaps the most common example of this is
the Juglone which is produced by the roots of the black
walnut tree (Juglans
nigra). |
alpine |
- in the strict sense, a plant
that grows
naturally on mountains above the tree line, but used
generally for any plant that is small and suitable for
use in a rock garden. True alpine plants usually have a
short growing season so they come up quickly as soon as
the snow melts, grow, set flowers and then go dormant. |
alternate |
- the
bud or leaf arrangement characterized by a single bud or
leaf per node alternating on different sides of a stem.
Most common tree species have alternate bud
arrangements. Examples include Birch (Betula),
Beech (Fagus), Oak (Quercus), Elm (Ulmus), Walnut (Juglans).
See opposite |
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alternate host |
-
certain fungal diseases (many of the rust diseases
for example)
survive part of the year on one type of plant and then
jump to a second type of plant for the remainder of the
year. For the disease to be active, both hosts must be
present in relatively close proximity.
An example is cedar-hawthorn rust which spends
the winter on the cedar (Juniperus
virginiana) and then jumps to the new leaves of
the hawthorn (Crataegus
spp.) in the spring and back to the cedar in the
fall. |
ammonium sulfate |
-
a single source fertilizer that contains 27 percent
nitrogen and has an analysis of
27-0-0. It helps acidify the soil and should be used for
plants in the family
Ericacae such as
rhododendrons, azaleas,
boxwood and other acid loving plants such as
blueberries and
pin oak. |
angiosperm |
- the major division of
plants that produce seeds that have a seed coat. See
gymnosperm |
anion |
- a
negatively charged ion (-) |
annual |
- an
herbaceous
plant which completes its life cycle within a single growing
season and then dies after producing seed. There is some
confusion in this matter since many of the plants we
purchase as "annuals" do not fit this definition. Most
of these plants are actually herbaceous
perennials which would normally live more than two
years but cannot survive the winter temperatures. Many
of these come from tropical or
at least warmer climates. If you can keep a
plant over the winter indoors under lights, it is not a
true (botanical) annual but is a
tender perennial. Examples would be
pelargoniums (sold as geraniums),
coleus,
impatiens and many others. See
Perennial and
Biennial |
annual ring |
- dicotyledon trees grow in girth (circumference)
through the action of the cambium layer building new
xylem and phloem cells. At the end of each growing
season, these new cells are thicker than others
developed earlier in the season and appear as a ring
when looking at a cross section of a tree trunk or
branch.
The age of a tree can be determined by counting the
annual rings in the main trunk of the tree. Also,
judgments may be made about the type of growing season
based to a certain extent on the width of the various
rings.
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annual
ryegrass |
- a
temporary grass with rapid germination; often found in
inexpensive grass mixes. Should not be used when
establishing a permanent lawn. May be used when you need
a "quick fix" such as a lawn wedding in two weeks but
this grass will die in the fall. |
anther |
- the male part of a flower is called the
stamen. It consists of a
filament or stem and a
capsule like structure at the top called the anther which
produces the yellow
pollen.
Hybridizers move the pollen from the male parent
to the
pistil of the female parent when cross-breeding
hosta,
Hemerocallis (daylilies) and other plants.
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anthocyanin |
-
this is a red pigment found in plants that produces red
leaves, fruit or other plant parts. In the autumn, it is
produced in certain
deciduous
trees if the weather is
warm during the day but cool at night. The variation in
temperature governs the type of fall color display. |
anthracnose |
-
disease caused by a fungi and
characterized by sunken lesions and black blotches
(necrosis) of the leaves.
ash,
white
oak,
sycamore
and
maples are trees
that are susceptible along with many other plants. In
bad years, sycamore trees may be totally defoliated by
this disease. Fortunately, they have the ability to
produce a whole new set of leaves by July. |
apex or apical |
-
(pl. apexes, adj. apical) tip of a root or shoot,
containing the apical meristem |
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aphicide |
-
an insecticide (i.e. poison) that kills aphids |
apical dominance |
-
influence exerted by a terminal (i.e. apical)
bud
on a
stem which suppresses the
growth of lateral buds on the stem below it. This
results in the "A" frame form of certain plants.
See
pinching |
apiculture |
- pertaining to the care and culture of
honeybees. Honeybees, of
course, are the agent for moving pollen from the stamen
of flowers to the pistil resulting in seed formation.
They are NOT required for a plant to merely produce
flowers. |
apomixes |
-some plants have the ability to produce seed without
having to have the egg fertilized by
pollen.
This asexual process
results in the seedlings being genetically identical to
the mother plant since there is no mixing with a male
flower.
In hostas, the species,
H. ventricosa
, is an example of a plant that
can produce seed this way. |
arboretum (arboreta) |
-
a place where trees and shrubs are grown either alone or
with other types of plants for scientific and educational
purposes. |
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arboriculture |
- the branch of
horticulture
or forestry
that deals with
the care and maintenance of ornamental trees and shrubs. |
artificial
soil mix |
- a "soil" or growing mix called a medium which is composed entirely of
peat moss,
vermiculite or
perlite, and
fertilizers, without any
mineral loam or field soil. Leaf mold
and bark are other materials used in artificial soil
mixes. |
asexual
propagation |
- plants have the ability to reproduce more individuals
without having to mix the genetic materials of two
flowers (i.e. sexual
reproduction). In nature, bulbs,
corms,
rhizomes, tuberous
roots, tubers,
offshoots and other
structures provide the avenue for asexual propagation.
New plants produced in this way are genetically
identical to each other.
This process is also called vegetative reproduction.
Humans have developed several asexual techniques for
multiplying plants. These include
grafting,
budding,
division,
layering,
cuttings and
tissue culture.
More on
Propagation |
auricle |
- an
earlobe-shaped appendage usually at the base of a leaf,
petal, or bract that is used
in the identification of
species of grasses. |
auxin |
-
a plant hormone that controls cell elongation
and also encourage the development of roots.
The most common auxins include
indoleacetic acid (IAA), indolebutyric acid (IBA), and
naphthaleneacetic acid
(NAA). They may be purchased in
various forms (liquid or powder) and strengths. Applied
to the cut end of a cutting
before putting (sticking) them
into the media will encourage root formation. |
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available moisture |
-
amount of moisture in soil
between the field capacity and the
permanent wilting
point that is available for use by plant roots. |
awl-shaped |
-
tapering gradually to a stiff, fine point,
as an awl-shaped leaf. |
axil |
- the
upper angle between a twig or leaf and the stem from
which it grows. |
axillary bud |
-
bud that develops in the axil of a leaf i.e. where
the leaf stem (petiole) joins with the twig or stem. See
lateral bud |
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