B horizon
- subsoil horizon where clay and mineral compounds accumulate. It is the layer beneath the topsoil called the A horizon.
Bacillus thuringiensis or Bt - a species of bacteria that infects and kills caterpillars in the Lepodoptera Family of insects i.e. larvae of moths and butterflies. The nice thing about it is that it does not affect other living organisms including other insects, animals or humans.

Bt is commonly sold as an insecticide under several brand names. It can be used for such pests as gypsy moth, eastern tent caterpillar, tomato hornworm and cabbage loopers. The only thing to consider is whether there are rare or endangered butterflies in your area. It does not discriminate whether the caterpillar it kills would have become a gypsy moth or monarch butterfly.

There are also other strains of this bacteria which are effective against mosquitos, Colorado potato beetles and other insect pests. Be sure to get the correct strain for the pest you want to control.

Be aware that Bt will NOT work on a class of insects called sawfly larvae. Although these critters look like caterpillars they are not. Therefore, Bt is not used for pests such as the European pine sawfly larvae.

background plant - a plant placed in the background of a flower border that provides a backdrop for the flowering plants in front of it. It could be related to the scenery at the back of the stage in a theater production. The background does not directly enter into the scene but adds to it in non-showy way. See Design...
backward mutation - variegation in a leaf means that for some reason, there is less chlorophyll present than normal resulting in tissue of a white, yellow or lighter green color than the rest of the leaf. A backward mutation or reversion occurs when a variegated plant actually gains chlorophyll in those lighter areas and returns to its original color scheme.
bacteria - simplest, smallest and most abundant single-celled organisms which are important to gardeners as decomposers and plant pathogens. In the compost bin, they help to decompose organic matter into compost. Although the vast majority of plant diseases are caused by fungi, there are a few serious plant diseases caused by bacteria including bacterial wilt, fireblight and wetwood.
balanced fertilizer - a fertilizer containing equal proportions of the macro-nutrients nitrogen (N), phosphorus (P), and potassium (K) such as a 12-12-12 formulation.

More on Fertilizers

balled-and-burlapped or
(B & B)
- a method of marketing trees and shrubs in which the roots and the surrounding ball of soil are wrapped with burlap and reinforced with rope or a wire basket. This is a technique usually used on larger plants and is meant to help keep as much of the root system as possible together during the transplanting process which helps minimize transplant shock.

More on Types of Nursery Stock

bare-root - a method of marketing plants in which the plants are not potted in containers and do not have any soil around their roots. Only deciduous plants such as fruit trees, roses and other dormant woody plant material should be sold in this manner. The only exception would be that small, evergreen seedlings may be handled bare-root also.

More on Types of Nursery Stock

bark - the outside layer of woody plants such as trees, shrubs and some vines is called the bark. It is made up of a protective tissue called the periderm. Also included are all the tissue outside the cambium such as the phloem
basidiomycete  - member of a class of fungi that form sexual spores.
basal - relates to the base or lower part of a plant tissue as in basal leaves that attach to the bottom part of the plant only. Sometimes called a rosette.

Also relates to the basal plant of bulbs such as daffodils or tulips.

bed - in vegetable gardening a bed may refer to an area where the soil has been prepared for planting something. In landscape design, a bed is an area for planting that is set away from the boundaries of the garden or landscape. A common type is called the "island bed" because it sits like an island in the sea.

Configurations that have a backdrop such as a fence, hedge or structure on one side are called a border.

- English nurseryman, Alan Bloom, is credited with popularizing the use of island beds in British gardens.

More on Beds and Borders

bedding plant - gardeners in England started the process of "bedding out" large numbers of plants into elaborated designs in the home landscape. Bedding plants are primarily annuals or tender perennials that are used for one season in the garden and then replaced the next.

Common bedding plants include petunia, zinnia, marigold, begonia, geranium (pelargonium), snapdragon, and sweet alyssum, as well as many, many other flowering plants.

Vegetable transplants are also lumped into this category at the local garden center.


- any insect of the Order Coleoptera, characterized by elytra (thickened outer wings), chewing mouthparts, and complete metamorphosis as part of its life cycle.

Japanese beetles and Colorado potato beetle are two well known plant pests in this group. The damage done by beetles is often characterized as "skeletonizing" the leaf i.e. eating the material between the veins but leaving the veins intact.

bell-shaped flowers - flowers that resemble a bell that hang with the opening in a downward direction.
bentgrass - a fine-textured grass that is difficult to maintain; best used on golf courses but not generally recommended for home lawns. In some cases, it may be considered a weedy grass when it becomes inadvertently  seeded into established lawns of other types of grasses.
berm - raised or mounded soil that is used for planting trees and other plants often for the purpose of providing a windbreak or as a way of delineating a boundary on a property. Sometimes, a berm is constructed to provide an elevation change in an otherwise flat landscape. Generally, it is best to make the height and base width of the berm in proportion so that it appears to be a natural change in the terrain to avoid the "pimple" effect.
bicolored - having two contrasting colors on the same petals of a flower.
biennial - a plant that requires two growing seasons to complete its life cycle (vegetative growth in the first year, reproductive growth i.e. flowers, in the second, followed by plant death). Some herbaceous flowers such as foxglove (Digitalis purpurea), Sweet William (Dianthus barbatus) and several common vegetable plants are biennial.

Note: At times I have seen the phrase "...acts as a biennial" which is always confusing. I think they probably mean that the plant is a short-lived perennial which is supposed to live more than two years but because of environmental conditions often only makes it a couple of years. In the end, a plant is either an annual, biennial or perennial and cannot really be more than one of these life cycle options.

See Annual and Perennial

binate - growing in pairs
binomial nomenclature system - the system of naming plants developed primarily by Swedish scientist Carol Linnaeus whereby every plant or animal type has a specific name consisting of two parts, the genus and species.

An example would be Hosta sieboldiana.


- determination of the relative toxicity or strength of a substance by comparing its effect on a living test organism with that of a standard preparation.

For example, Colorado potato beetles are often resistant to several common insecticides, so a simple bioassay is often needed to determine which one is effective on the local population of beetles at what rate of application. Some beetles are placed in large, covered petri dishes, each of which contains a different pesticide. If the beetles are killed, that indicates that insecticide would be effective on those particular local insects.

biological control - a method for controlling plant diseases or pests using naturally occurring predators, parasites or diseases. For example, the use of the bacteria called Bacillus thuringiensis or Bt which causes a fatal disease in caterpillars such as gypsy moth or cabbage loopers.
biotic - the term applies to any living cause for a plant problem. Animals, insects, spider mites, fungi, bacteria, etc. would be considered biotic causes of plant damage.

Nutrient deficiency, nutrient toxicity, physical damage, weather impacts, poor drainage and other non-living factors would be called abiotic.

bipinniate - said of a leaf that is twice pinnately compound.
blade - the flat, expanded portion of a leaf which is connect to the stem by the petiole.
blackvine weevil - a night-feeding insect (Otiorhynchus sulcatus) which is a common pest of rhododendrons, yews and hostas. It causes a characteristic "half-moon" shaped notch on the edge of the leaves. The larvae also feed on the roots of plants and may be a more serious problem than the foliage feeding by the adult weevil.
blend - a combination of grass seed consisting of two or more cultivars from the same species or from separate species. An example would be a mixture of Kentucky bluegrass, perennial ryegrass and fine fescue seed which is commonly used in home lawns. This prevents the establishment of a monoculture which may lead to more serious pest and disease problems.
blight - a term generally associated with diseases that cause severe damage to plants, especially to lush, new growth. Fireblight is a bacterial disease of members of the Rosaceae Family. Diplodia tip blight is a fungal disease of certain pine species. There are many other examples that affect buds, leaves, blossoms and shoots of plants in the landscape.
bloom - 1) bloom may refer to the opening of the flowers on a plant.

- 2) bloom also relates to the waxy coating on a leaf, stem, or seedpod surface producing a dusty appearance which often reflects blue light waves. The blue color in hosta or Colorado blue spruce trees is the result of a waxy bloom on the leaf or needle surface. Over the growing season, this wax may wear off and the green color of the plant tissue beneath may become dominant.

bloom season - the time period between when the first flower of a stem or clump opens or is receptive to pollination and the last flower on the plant closes.

For example, individual species and cultivars of hosta have specific bloom times ranging from late May to late autumn depending on the relative location of the garden.

blotch - an irregularly shaped discoloration which may be caused by disease or physical damage. This will help distinguish symptoms from other diseases which may produce circular or regular shaped discolorations such as a ring spot.
bolting - this is a term used when a biennial plant flowers during the first season rather than in the second season of its life cycle. It is usually caused by some type of stress on the plant such as drought, excessive heat, etc.

In vegetables, bolting is undesirable in such plants as Brussels sprouts, cabbage, carrots, cauliflower, celery, chard, collard, endive, kale, kohlrabi, leek, onion, parsley, parsnip, rutabaga, salsify, and turnips. The flower stalks detract from the vegetable production.

However, bolting is a good thing in ornamental biennials such as foxglove (Digitalis purpurea) where it is preferable that many of the plants flower in the first season rather than having only foliage the first year and blooming in the second as is normal for a true biennial.

Bordeaux mixture - a few centuries ago, the French discovered that a mixture of lime and sulfur when applied to their grape vines would help to minimize certain fungal diseases. They named it a Bordeaux mixture for the region of France and it was probably the world's first fungicide.

It is made with quicklime and copper sulfate. The quicklime is rather caustic so, if it is not mixed at the correct strength, it will burn the leaves of the plants. It can also be tough on spray equipment but does qualify as an "organic" alternative for control of certain (but not all) fungal diseases.

border - a place where ornamental plants are arrange next to a backdrop such as a wall, fence, building or hedge. Generally, the taller plants are in the rear next to the backdrop with a gradual decline in plant height toward the front. Borders are viewed only from the front in contrast to a bed which may be viewed from all directions.

More on Beds and Borders


- insect or insect larva that makes tunnels or cavities into the bark or within the wood of trees. They leave holes of various sizes and shapes in the bark as the adults emerge from the tree.

Most native borers infest trees that are already under stress because of drought, age, disease, etc. They are part of nature's scheme to reclaim trees back into the soil.

Some exotic borers such as the Emerald ash borer and Asian Longhorned Beetle will attack healthy trees which makes them especially lethal pests.

botanical insecticide - as the name implies, these are substance that are produced from plants and that kill insects. Many of them are natural and come directly from the plant such as the pyrethrums, nicotene, rotenone, ryania and neem oil. However, chemists have duplicated some of these compounds in the laboratory so, even though they may have the same name as a naturally occurring type, some commercial products may be "man-made" or synthetic.
botany - the plant science that is concerned with the study of non-cultivated (wild) plants.

Horticulture is a more narrow science devoted to plants with an economic value for fruit, vegetables or ornamental uses.

bract - an often showy modified leaf that forms on certain plants. The white or pink color on a dogwood tree is actually a bract as are the red parts of a poinsettia. Certain hostas form a bract on their flower stems.
bramble - plants belonging to the genus, Ribes; commonly used to refer to raspberries and blackberries.
branch collar - the raised hump located where a branch attaches to the trees trunk or a larger branch. In pruning large branches with a saw, the cut should be made just outside of this collar rather than using a flush cut method which will damage the tree.
broadleaf evergreen - ornamental plants with comparatively broad or wide leaves that remain on the plant and green throughout the year, such as rhododendron, holly, English ivy, Oregon grape holly and boxwood.

Contrast with Narrowleaf Evergreens

Broad-spectrum - this is a pesticide that kills a wide range of target and non-target organisms when applied to a landscape. The movement in recent decades has been toward more narrow spectrum pesticides that are targeted to kill a small number of specific organisms.

Bacillus thruingiensis (Bt) for example, is an insecticide which only kills caterpillar members of the insects family, Lepodoptera.

brooming - see Witche's broom.
bryophytes - non-vascular plants including the mosses and liverworts.

- a rudimentary shoot or flower; may he either vegetative (developing into leaves or stems), flowering (producing one or more flowers), or mixed (containing both leaves and flowers). Some buds are adventitious which means they wait in reserve to see what is needed by the plant before developing into either leaf or flower buds.

bud blast - death of a flower bud before it opens. The main causes are frost or freezing, water stress, pollution, and insect damage.
budbreak - the stage of bud development when green tissue becomes visible in the spring.
budding - the propagation of a plant by inserting i.e. grafting, a dormant bud (scion) of one plant into the stem (rootstock) of another. If the cambium layers of the two parts are properly aligned, they will eventually join to form a single plant.
bud scale - a modified leaf that covers and protects a bud. This characteristic may be used to help identify various species of plants. The bud scales of European Hophornbeam (Ostrya virginiana), American Hophornbeam are striately marked while those of American Hornbeam (Carpinus caroliniana) are smooth.
buffering - the chemical characteristic of a soil that prevents large swings in soil chemistry. This may be both beneficial or detrimental in regard to plants. Buffering qualities of a particular soil may make it very difficult to lower the pH i.e. make it more acid, by adding sulfur products.

1) slang for an insect

2) plant bug is an actual group of insects from the Order Hemiptera which are characterized in part by piercing-sucking mouthparts, a triangular scutellom (hard plate on the thorax), two pairs of wings, and gradual metamorphosis.

One of the most damaging of these for the home gardener is the four lined plant bug. This is what causes those roundish, black spots on the leaves of chrysanthemums, coreopsis and many other plants.

bulb - in horticulture, many things are incorrectly lumped into the category called "bulbs" including corms, tubers, tuberous roots or storage roots. A true bulb is a swollen underground bud formed from fleshy scales or leaf bases that enables various plants to rest in a dormant state for part of the year. True bulbs include tulips, daffodils, lilies (not daylilies), alliums (ornamental onions) and many others.

Images of Bulb Plants.

bulbil or bulblet - a small, immature bulb, generally forming at the base of a parent bulb but sometimes above ground in leaf axils (known as aerial bulbils) as in some types of lilies.

- in the spring when the buds on the top of the hosta crown begin to expand and emerge from the soil, they form what are called "bullets."  Before the leaf blades enlarge and unfold to open, they resemble the business end of a rifle cartridge.

burn - this is a term that is often used in regard to plants but is not well understood by the average gardener. Of course, there is no combustion involved when a plant gets "burned" in the garden. Rather, what we are talking about is rapid dehydration that causes plant tissue to die and turn brown.

Generally, this occurs when a chemical salt is placed in close proximity to plant parts, especially their roots. Most fertilizers are chemical salt compounds and fresh manure (not composted) also contains a lot of salt. When a clump of fertilizer or fresh manure comes into contact with a root, water is rapidly transferred out of the root and into the salt. This causes plant cells to burst and die resulting in browning to plant tissues. In extreme cases, the entire plant will die.

bushel - volume of media containing 1.25 cubic feet or 35.7 liters. Consists of 4 pecks as in "I love you a bushel and a peck..."

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