A

Aeration – Introducing air into the soil by making holes in it or pulling cores of soil out of it.

Aerification – The mechanical removal of soil cores.

Algae – Any of a group of chiefly aquatic lower plants without root, stem, or leaves, classified by color.

Aphids – Any of various small insects, such as the greenfly, that suck the juice of plants.
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Appressed – Lying close and flat against, as a bud against a twig.

Auricle – Ear-shaped appendage

Awnless – Without the beard or bristle-like appendage of the outer glume of numerous grasses.

Axillary – Springing from, or positioned in the angle formed by the upper side of a branch with the stem or trunk to which it is attached.