It is a variable species, with individuals and populations of differing bulb size, flower colour, leaf coloration etc. In general it produces a large bulb, 10 to 15 cm in diameter, covered with firm, hardened, papery brown or purplish tunics (bulb scales). It is deciduous, growing during summer and dormant in the winter.

A rosette of 6 to 9 broad, tapering leaves emerges from the top of the bulb in spring. The leaves are attractive in their own right, with clearly distinct veins which give them a two-tone effect, particularly when back-lit. Their colour is light green with white-grey overtones, they can be entirely green, or they can have purplish colouring on the margins, at the base or at the apex of the leaf, or the underside can be partially or entirely shaded with purple. They can be completely hairless, or one or both sides can be covered in short hairs. The leaves of a well-grown plant can reach a height of 30 to 50 cm with about equal spread.

The inflorescence is a many-flowered slender raceme of bright violet-blue, or pale blue, or blue and white, star-shaped flowers each one carried on a delicate amethyst blue stalk, giving the overall effect of a misty blue plume floating in mid-air. There is also a white form, although we don't have specimens in the Garden as yet. The flower stalks are produced either just before or with the new leaves in spring to early summer (October), and are usually about 1 m tall, although some are as short as 0.75 m and a few can reach a height of about 1.4 m. The flowers have a honey-like scent towards evening and are visited by bees during the day. The seed, which is formed in capsules that split when mature, does not look much like seed. It is beige in colour, somewhat irregular in shape and a bit wrinkled, 6 mm long x 2-3mm wide tapering to a point. It is light in weight and dispersed by the wind. It does not last long unless it is refrigerated (not frozen) where it will last for a number of years.

Merwilla plumbea has shown itself to be selectively toxic to mammals. It is said to be poisonous to stock, particularly when the young leaves appear in spring. Experiments on sheep, using fresh bulb as a drench, proved fatal to the sheep, yet it has been proven an ineffective rat poison. It is apparently toxic to man when raw, even the sap is reported to burn the skin, and for any preparations taken internally the plant must first be heated. This plant should be treated with extreme caution, as taking any part of it internally is potentially fatal.