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Despite its name, an asparagus fern is not a true fern, but an edible member of the lily family that is closely related to asparagus. Asparagus densiflorus has been grown as a houseplant for over a century. This plant thrives in shade and can survive dry conditions. In many parts of the world, it has become an invasive plant species.
There are several cultivars of Asparagus densiflorus that are commonly grown. One is Sprenger’s asparagus, or Sprengeri. The other is the foxtail asparagus fern, known as the cultivar Meyeri.
Asparagus ferns all grow from a mass of roots that have bulbous tubers. These tubers can be the source of new plants. What appear to be leaves are actually cladodes — thin, flattened stems that grow to between 0.12 in (3 mm) and 1 in (2.5 cm) long. The true leaves are actually small spines.
The growth patterns of the asparagus fern cultivars are very different. The foxtail asparagus fern has thick, bushy stems that grow to 2 to 3 ft (0.6 to 0.9 m) long, giving it the appearance of a fox’s tail. Sprenger’s asparagus forms clumps that trail or form mounds 3 to 6 ft (0.9 to 1.8 m) long.
All of these types of asparagus ferns bloom in the spring with small, white flowers that are found all through the plant. In the summer, they produce red berries that are 0.5 in (1.3 cm) across. All parts of the plants are toxic to dogs and cats.
The asparagus fern has been a popular houseplant for over 100 years. Individual plants can grow to be very old and become family heirlooms. These types of plants are commonly used as patio plants or indoor houseplants. Inside, they prefer bright light without direct sunlight. Ideal temperatures are 50 to 55° F (10 to 12.8° C) at night and 68 to 72° F (20 to 22.2° C) during the day.
Plants should be watered every week or two. Established plants should be fertilized at three to four month intervals. The ferns should be repotted if they are overcrowded. They can be propagated by division.
Outdoors, Sprenger’s asparagus is more hardy than the foxtail asparagus fern, growing at temperatures down to 24° F (-4° C). Often, if a plant freezes to the ground, it can resprout from its tubers. It is through these tubers that asparagus ferns can survive drought, but they grow better when watered on a regular basis. In areas with cool summers, they thrive in sun, but otherwise prefer shade. The plants are perennials in warm climates.
Asparagus ferns grown in subtropical or tropical gardens may require care to prevent them from escaping to wild, or non-landscaped, areas. The plants are a weed in their native South Africa. They have also become invasive in the United States, in Florida and Hawaii. Australia and New Zealand are other areas in which they have escaped cultivation.