“E” horizon - transition zone in the soil where organic matter does not accumulate and clay and mineral compounds (e.g., iron, aluminum) leach out.
edging plant - a plant used along the front edge of a bed or border. They usually have a mounded appearance, lending softness to the bed or border margins.
elliptic - oblong, narrowed to rounded ends and wider near the middle.
emerged - a plant that has shoots above the ground surface.

- as hostas emerge in the spring, the first growth is called the "bullet." Some cultivars emerge so early that they may suffer frost damage which will tatter the leaves as they open.
entire - a leaf margin with no teeth or crenations i.e. rounded teeth.
enzyme - protein that starts (acts as a catalyst) a specific biochemical reactions in a living organism.
EPA - Environmental Protection Agency - The Federal agency responsible for pesticide rules and regulations, and all pesticide registrations.
epidermis - outermost layer of cells on plant parts such as leaves and stems
epinasty - twisted, gnarled growth on plants which can often be caused by exposure to the herbicide, 2,4-D. Some plants (tomatoes for instance) are extremely sensitive to this herbicide and even a small drift from a nearby application to the lawn or use of Weed-N-Feed fertilizers will cause this distorted growth.
epiphyte - plants that live on other plants but are not parasites. They get their moisture and nutrients from the rain and air. Often, their nutrients come from decaying organic matter caught in cracks or crotches of the tree that they live upon. Most, but not all, epiphytes are native to the tropical or subtropical regions of the world.
ericaceous - refers to the heather or heath family (Ericaceae) and includes plants such as rhododendrons, azaleas and boxwood. Members of this group are noted for their need of acid soils with a pH in the range of 4.5 to 6.0 for proper growth.
erosion - the movement of soil particles away from the site, causing a loss of topsoil. This can be caused by wind or water.
 
espalier - method of training a woody plant to grow in a single plane against a wall, trellis, fence or other flat surface. This may be done to grow fruit in a small space or for ornamental purposes.

More on Espalier
essential element - certain elements or nutrients must be available in specific amounts for plant growth or the plant will develop deficiency symptoms. Generally, there are 16 nutrients which are considered vital for plant growth.

Some of the essential elements are required in relative large amounts by the plants and these are called macro-nutrients. Others are still required by the plant but only in small amounts and these are the micro-nutrients.

More on Plant Nutrients
established plant - an established plant is one that has been in its current site long enough to have developed the required root system and is producing the expected growth of leaves and stems. If it was recently moved, it has survived transplant shock.
ethylene - this is a naturally occurring gas with the chemical formula of C2H4.. It is produced by plants to promote ripening of fruit and by plants as they senesce and begin to decay.

A commercially prepared form of ethylene is used to artificially begin the ripening process in tomatoes in storage. Care should be taken to not store ripening fruit in the same area as cut flowers because ethylene will cause them to drop their petals.

See Hormones
etiolation - when plants are not exposed to the amount of light they require for proper growth, they will produce excessively long, weak (spindly) shoots and stems. This process is called etiolation and the plants are said to be etiolated.
 
evergreen - a plant whose foliage remains green and functional for more than one growing season. The two categories are narrow leaf evergreens (pines, spruce, fir) and broad leaf evergreens (rhododendron, boxwood, wintercreeper).
explant line - an explant is the "mother plant" from which a cutting is taken during tissue culture propagation. The "line" constitutes the plants that result from the process.
exudate - substance such as sap that is excreted or discharged from a plant.
eye - this is commonly used to identify an undeveloped or dormant bud on a stem or stem modification such as a tuber (potato) or corm (gladiolus, windflower). In propagation of these types of plants, you must have at least one eye on each piece that you are dividing.
 

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