palmate |
- shaped like the open palm of a hand having four or more
lobes (fingers) or leaflets radiating from a single
point. |
panicle |
- flowers are borne on a structure called the
inflorescence.
The peduncle is the main stem of
the inflorescence. When this stem has branches, the
structure is
called a panicle.
The species,
Hosta tibiae have its
flowers borne on panicles. |
parallel |
- lines running in the same direction and equal distance
from each other at all points. Plants in
the
monocotyledon
(grasses, hostas, etc) category have parallel veins. See
dictotyledon. |
parent material |
-
the rock layer from which a mineral soil originated.
|
pathogen |
- a disease-causing agent. In plants the vast majority
of
diseases are caused by fungi while a few are caused
by virus,
bacteria,
mycoplasma and others. |
peat moss |
- from the day they are formed, mother nature wants to
fill in lakes and ponds. Over thousands of years, the
water plants die and sink to the bottom of the lake and
eventually fill it with decomposed
organic matter called
peat moss.
Depending on the type of plants that grew in the bog, the peat moss will have varying textures.
Sphagnum peat tends to be coarse textured while
so-called Michigan
peat is very fine textured.
Peat moss is used as a soil amendment in the garden
but is most often used as part of soilless media used in
pots and containers. It is combined with
perlite and
vermiculite to form a light, well-drained media that
holds onto
nutrients. |
|
|
pedicel |
- the "stalk" that attaches
an individual flower to the peduncle
which is main stem of the
inflorescence. |
peduncle |
- flowers are borne on a
structure called an
inflorescence. The peduncle is the main stem
of an inflorescence of flowers.
|
percolation |
- the slow movement of water through the pores in soil
or permeable rock layer. |
perennial |
- one of the natural life cycles of plants where the
same plant lives for more than two years. The number of
years a plant lives may vary widely.
Within perennials there are two subgroups:
1) Woody perennials
would include trees and
shrubs that form solid, woody
tissue that persists from year to year. Trees, of
course, may live hundreds or, in a few cases, thousands
of years.
2) Herbaceous
perennials form soft, non-woody tissue that may
persist in tropical or
subtropical climates or
dies to the ground in
temperate regions.
Herbaceous perennials may
live decades (peonies,
hostas) or just a few years
(delphinium,
gaillardia).
See Annual and
Biennial Images of
Perennials. |
perennial ryegrass |
- a common turfgrass species for northern lawns. It is
noted for rapid establishment and tolerance of wear.
Ryegrass is generally a finer textured grass and it is
relatively shade tolerant.
Perennial ryegrass is
commonly combined with
Kentucky bluegrass
and fescue in
cool-season grass seed mixtures for the home landscape
in temperate regions. |
|
|
perfect flower |
- a flower that has both male (stamen) and female
(pistil) parts in the same blossom. It is also called a
complete flower.
|
perianth |
- collectively, the petals and
sepals of a flower taken
together. In most flowers, the sepals are green and a
different color from the petals. In some plants,
however, the sepals are the same color as the petals.
|
pericarp |
- this is the wall of a fruit that encases the seeds. |
periderm |
- secondary protective tissue that replaces the
epidermis when it is destroyed during secondary
growth; includes cork and cambium. |
perlite |
- a material made from volcanic rock (lava) which is very light and porous.
It is formed in a very hot process at 1,400 degrees F so
is completely sterile. Perlite helps to provide more air
and water pore spaces in artificial growing media when
combined with peat moss.
Care should be taken with using this product in the
garden because it is very light and may be blown around in the
wind. Also, all the white specks mixed into the soil makes it
look unnatural. |
|
|
permeability |
- the capacity of a porous rock or soil
to permit the flow of water through its pore spaces.
Clay has low permeability while sand is highly
permeable. |
permanent wilting
point |
- as soils dry out, they eventually reach a point where
the water is held so tightly to the soil particles that
it is no longer available to the roots of plants. The
cells of the plants will begin to collapse and the
addition of water to the soil at this point will not
revive those cells. |
pesticide |
- the suffix, icide, means "to kill".
Pesticides are
therefore, substances that are meant to kill pests. This
is a general term that encompasses a wide variety of
materials including insecticides,
herbicides,
fungicides,
miticides,
rodenticides and others. |
petal |
- generally the colorful part of a flower that is
located between the outer (often green)
sepals and the
stamen and/or
pistil on the inside of the flower. The petals of
hosta generally range in color from pure white to
dark purple. Violet and lavender are also terms used to describe
hosta flowers. Some cultivars have dark stripes on lighter
colored petals.
|
petaloide |
- petal-like in shape, texture and/or color but not
actually a petal. |
petiole |
- the stem or stalk that supports
the leaf blade.
When
deer eat
hostas, they generally eat the blade
but leave the petiole looking like celery stalks. Most
petioles are the same basic color as the blade but some
hosta
cultivars have
purple or speckled ones. |
|
|
pH |
- a chemical measure of acidity or
alkalinity using a
0 to 14 scale. Substances with a pH of 7.0 are neutral.
Those below 7.0 are said to be acid and those above 7.0
are called alkaline or base. The scale is logarithmic
meaning that each unit is ten times greater than the
previous unit.
For example, a pH of 6.0 is ten times as acid as a pH
of 7.0. A pH of 5.0 is 100 times more acid than one of
7.0. Dropping to a pH of 4.0 is 1,000 times as acid as a
pH of 7.0.
For the gardener, pH of the soil is important because
it has an impact on how effectively the plant can use
available
nutrients from the soil. The vast majority of
plants grown in the temperate zones perform best in a
slightly acid soil somewhere between 6.0 and 7.0.
A few plants, most notably those in the
Ericaceae
Family, prefer a highly acid soil in the range of 4.0 to
5.5. In the landscape, this would include
rhododendrons
and
azaleas, heaths, heathers,
boxwood
and
pin oak among
others.
If the soil pH is outside the preferred range for a
plant, it will be unable to absorb nutrients even if
they are in the root zone. A classic example would occur
when
rhododendron leaves turn yellow
but still have dark green
veins. This indicates an iron deficiency but a
soil
test might actually show plenty of iron in the soil. The problem
is usually that the pH of the soil is neutral (7.0) or
alkaline and the plant is just not able to take up the
available iron.
|
phenotype |
- the physical appearance of the plant which may be
observed visually. The phenotype may or may not be directly related to the genetic
makeup (genotype) of the plant. For
instance a plant resulting from the cross of a red
flowered plant and one with white blooms may have pink
blossoms. However, genetically, it would carry some
genes for red and white flowers. |
pheromone |
- chemicals secreted by
insects (or other
animals
including humans) that provide a type of communication between
individuals of the species. The most common pheromones of interest to
gardeners are insect sex attractants which are excreted by
females which may draw males to them from miles away.
For example,
gypsy moth females do not fly.
To attract the male moth which can fly, they excrete a
strong pheromone. Male gypsy moths will be drawn to them
from as much as a mile away. Another use for
pheromones is to draw certain insects into traps so that
their populations may be monitored. Commercially
produced pheromones are used to monitor gypsy moth build
up in an area. Pheromones are also used as an organic
way to control certain pests of fruit trees. Tags
containing pheromones are attached to branches in large
numbers. There is so much pheromone saturating the area
that the males become confused and few of them actually
find the females. Studies have shown that this can help
to reduce certain pest species without having to spray
pesticides. |
phloem |
- a liquid conducting tissue in plants, the chief function of
which is moving carbohydrates and sugars from the leaves
downward toward the roots. See
xylem. |
phloem necrosis |
-
a fatal disease also known as elm yellows. |
|
|
phosphate |
- a chemical compound with the formula P2O5.
In fertilizers, this is the form of phosphate that
is actually in the bag i.e. 10-15-10 has 15% phosphorus
in the form of phosphate. |
phosphorus |
Phosphorus (P) is one of the
macro-nutrients (i.e. needed in relatively large amounts).
Generally, it is used in production of flowers and
roots.
A
fertilizer bag with the numbers 15-10-20 on it
would include 15% nitrogen (N), 10%
phosphorus (P) in the
form of phosphate (P2O5) and 20%
potassium
(K) in the form of potash (K2O).
Phosphorus, like potassium, has
a strong electrical attraction to the
clay particles in
soil. Therefore, in many gardens, it may build up to optimum levels over years of
application. In these cases, you may only need to apply
nitrogen in subsequent years. As
always, the only way to know how much of each element
you need for your particular crop (lawn, flowers, fruit,
vegetables, trees, etc.) is to complete a
soil test. |
photosynthesis |
- Plants are different from animals and the process
called photosynthesis is probably the key factor that
separates the two life forms. Green plants are the
organisms that capture energy from the sun and
incorporate it into carbohydrates and sugars. This
supports all life on the planet earth (science has
recently discovered some very, very minor exceptions)
Green plants take the energy of the sun i.e. light, in the presence of
chlorophyll
and combines it with water, carbon dioxide (CO2) and mineral
elements to form carbohydrates and sugars used for plant
growth. It releases excess oxygen from the water into the air which we
animals can breath in before we exhale carbon
dioxide.
Each plant has a minimum requirement for light,
nutrients, chlorophyll, water and temperature for photosynthesis
to take place. If any one of these factors is below the minimum
for that species of plant, photosynthesis will be at a low rate
or will not occur. For instance, If the plant is not getting the light that it
needs, adding fertilizer will not help.
Shade plants are those which have a low minimum light
requirement. They are NOT shade LOVING since they cannot
grow in the dark but are actually shade TOLERANT and are
adapted to low light environments. |
phototropism |
- basically, this is the attraction of plants toward the
light. It is why they usually (but not always) grow
upward. |
physiological
functions |
- this is a catch-all term for all of the processes that
go on within a plant during its life. This would include
photosynthesis, building
carbohydrates and
sugars, creating new plant
tissues, respiration,
absorption of water and nutrients, exchange of gases
with the atmosphere, etc. etc.
Plant problems that cannot be attributed to
insects,
diseases or physical environmental (abiotic)
factors are often called physiological problems. |
phytotoxic |
- anything that is harmful to plants but is usually used to describe
the impact of chemicals on plants |
|
|
picotee |
-
originates from the French picoté, meaning "marked with
points". In
horticulture, it is used to describe a
flower that has a different color on the edge of the
petals. They usually have a pale ground color with a
darker or brighter band around the edge of the petals. |
piecrust |
- (in
hosta) a consistent rippled
or crimped appearance limited to the outer edge of a leaf. Looks
like a piecrust at the edge of the pan. |
pinching |
- removal of the growing tip (terminal
bud) of a plant in
order to allow the axillary (lateral) buds to
grow. The result is a more bushy, compact plant with
more stem tips which are usually sites for flowers. |
pinnate |
- compound leaf resembling a feather with
leaflets arranged
on both sides of a common axis. Examples include
Kentucky Coffeetree (Gymnocladus),
Honey Locust (Gleditsia)
in certain instances. |
pistil |
- the female sexual
reproductive organ of a plant. It consists of the
stigma,
style
and ovary. Pollen lands on the stigma, forms a
pollen tube down the style and into the ovary. The eggs are in
the ovary and when the pollen reaches them, fertilization occurs
and seeds result.
|
pith |
- this is the tissue in the center of a
dicotyledon trunk or
stem. In some species, this becomes hollow which may be
an identifying characteristic.
Forsythia types can be separated by the texture and
arrangement of the pith. Several closely related
Cornus species can be identified by pith color
such as the Silky Dogwood (C. amomum)
which has brown pith while the Bloodtwig Dogwood (C. sanguinea)
which has white pith.
|
|
|
plant classification |
- in the past, as more and more new types of plants were
"discovered" it became obvious that a system had to be
developed to give each one a unique name so that proper
identification could take place. Early systems often
resulted in names with 10 to 20 words to describe just
one plant. This was way to complicated.
Carl Linnaeus from Sweden proposed a relatively
simple system based on the number of
stamens and/or
pistils in a plant's flower. Also, each plant (or
animal) would have a species name that consisted of only
two parts, the genus and a
specific epithet.
This classification system known as
binomial
nomenclature was finally adopted worldwide after decades
of debate. Today, if you write about a plant called
Monarda didyma, plant people all over the world
will understand. If you used one of its many
common
names such as beebalm, Oswego tea, bergamot, red balm,
crimson beebalm or horse mint, the chance for confusion
is much greater. |
pod |
- the name for the fruit of many plant
species. After the ovaries are fertilized by
the pollen, the petals drop off the flower and a pod develops
which encompasses the seeds.
Hosta pods resemble very small
cucumbers hanging on the peduncle. They may be of different
colors on the outside. The seeds, when ripe, are dark brown or
black with a small wing. |
pollarding |
- the practice of pruning tree branches back
to the same, uniform length every year. Although
this is commonly practiced in
Europe, it must be done
properly and with the correct tree
species to work. It
is generally not a recommended practice for most types
of landscape, ornamental trees. |
pollen |
- 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 pollen which is equivalent to the sperm in
animals.
Hybridizers
physically move the pollen from the male parent
to the
pistil of the female parent when cross-breeding
Hosta,
Hemerocallis (daylilies) and other plants. In
nature, this is done by
bees and other
insects that fly
around from flower to flower. Bats and other animals
also act as pollenizers in other parts of the world.
|
pollination |
- the transfer of pollen from
the male reproductive organ (stamen) to
the stigma at
the top of the female reproductive organ (pistil). |
poly |
- prefix meaning “many” |
|
|
polygamo-dioecious |
- a dioecious plant has separate male (staminate) and
female (pistillate) flowers on
different plants.
A polygamo-dioecious plant will
also have some perfect flowers (having both male and
female parts) on each plant. Examples include
Honeylocust (Gleditsia),
Ash (Fraxinus),
Fringe Tree (Chionanthus),
Osmanthus and
Mulberry (Morus). |
polygamo-monoecious |
- a monoecious plant has separate male (staminate) and
female (pistillate) flowers on the
same plant.
A polygamo-monoecious plant will also
have some perfect flowers (having both male and female
parts) on each plant. |
pome |
- a fleshy fruit found only in members of the
Rosaceae
Family; e.g.,
apple,
quince. |
pomology |
- the division of
horticulture
that deals with the science of cultivating fruit.
This includes both tree fruit (apples,
peaches,
pears,
etc.) and small fruit (strawberries,
raspberries,
grapes,
currents, etc.). |
postemergent herbicide |
- a herbicide which kills plants that are emerged from
the ground and actively growing. They will not kill
seeds in the ground. See
pre-emergence herbicide. |
potash |
- a chemical compound with the formula K2O.
In fertilizers, this is the form of potassium that
is actually in the bag i.e. 10-15-20 has 20%
potassium
in the form of potash. |
|
|
potassium |
Potassium (K) is one of the
macro-nutrients (i.e. needed in relatively large amounts)
necessary for plant growth.
Generally, it is used in "physiological functions" of
the plant which means that it is needed for the plant's
chemical processes somehow. It is also used in seed
production. A
fertilizer bag with the numbers 15-10-20 on it
would include 15% nitrogen (N), 10%
phosphorus (P) in the
form of phosphate (P2O5) and 20% potassium
(K) in the form of potash (K2O).
Potassium, like phosphorus, has
a strong electrical attraction to the clay particles in
soil. Therefore, in many gardens, it may build up to optimum levels over years of
application. In these cases, you may only need to apply
nitrogen in subsequent years.
As
always, the only way to know how much of each element
you need for your particular crop (lawn, flowers, fruit,
vegetables, trees, etc.) is to complete a
soil
test. |
pre-emergent herbicide |
- a herbicide that
prevents seed germination and/or
seedling emergence. It
has no effect on the plant once it has emerged from the
ground.
See postemergent
herbicide. |
primary infection |
- the first infection of a plant which
usually occurs in early spring by a pathogen that has overwintered
on the site.
Apple scab is a fungal disease of
apple and
crabapple trees. If the primary infection is prevented
when the leaves first unfold from the
bud, further
infection later in the year will be diminished greatly. |
progeny |
- the offspring from sexual
reproduction. It is usually the result of the combination of
genetic material from two individuals which leads to genetic
variation in the offspring or progeny. |
protectant |
- a material that is applied to a leaf surface before an
infection. Most fungicides act as protectants and
must be on the leaf when the fungal spores land to be
effective. Once the fungal spores have germinated, the
fungicide will not "cure" them but will prevent
spreading to uninfected leaves. |
pruinose |
- See
glaucous |
puckering |
- See
seersuckering |
pyramidal |
- the width of the plant is greatest near the ground and
tapers to the apex of the plant |
|
|