Asparagus fern

About Asparagus fern

Asparagus fern isn't a fern at all but a cousin of garden asparagus from southern and eastern Africa, with feathery 'leaves' that are really flattened stems, wiry spiny stems and thick water-storing tubers (Wisconsin, NC State). Sprenger's asparagus (A. aethiopicus, sold as A. densiflorus 'Sprengeri' or 'Meyeri') arches from hanging baskets, while the plumosa or lace fern (A. setaceus) is finer and climbs. Birds spread the berries, and in Florida A. aethiopicus is a Category I invasive that UF/IFAS says not to plant in landscapes; the berries are poisonous to people and pets.

Hardy outdoors in about zones 9-12 (NC State for A. setaceus; Wisconsin says Sprengeri types from zone 9, with roots often surviving to zone 7 if protected). It is grown indoors everywhere and can summer outdoors in shade once nights stay above about 50-55 F; it is a listed invasive in Florida and on a watch list in California, so keep it potted in warm states.

When to plant

Timing is counted from your average last spring frost (and first fall frost). Sow & Tell works out the actual dates for your ZIP code.

Usually bought as a nursery plant or hanging basket, or started by dividing the tuberous roots in spring; seed sprouts in 3-4 weeks at room temperature (Wisconsin, NC State).

Growing it indoors

• Light: Bright light, even some direct sun for Sprengeri types, gives dense growth (Wisconsin, UMN), while the plumosa fern wants bright indirect light out of hot sun (NC State); poor winter light makes it stretch and drop its needles.
• Water: Keep the mix consistently moist while it grows and a little drier in winter (Wisconsin). Both bone-dry and soggy mix make the needles yellow and drop, and overwatering rots the roots (NC State), though the water-storing tubers forgive an occasional missed watering.
• Humidity: NC State says the plumosa fern needs high humidity: use a humidifier or a pebble tray, since dry air browns the tips.
• Temperature: NC State gives 55-70 F as the preferred range and brings plants in when nights near 55 F; MU Extension lists 50 F nights as the low end.
• Feeding: Feed monthly from spring, when new growth starts, through summer, and stop in winter (Wisconsin).
• Repotting: It outgrows pots fast and its strong roots can break them, so repot often, in early spring before new growth, into a larger, thick-walled pot (Wisconsin, NC State).

Soil

A moist but well-drained potting mix rich in organic matter (peaty for the plumosa fern), in a sturdy pot, since the tuberous roots can crack thin containers (NC State, Wisconsin).

Pot in a moist, well-drained mix rich in organic matter (peaty for the plumosa fern) in a sturdy, thick-walled pot (NC State, Wisconsin).

Feeding

• Spring, as new growth starts, through summer: balanced houseplant fertilizer. Feed monthly to encourage new growth (Wisconsin); follow the label.
• Winter: none. Stop fertilizing and keep the mix a little drier (Wisconsin).

Yellow, dropping needles are usually a light or watering problem, not hunger, so fix those before feeding more (NC State, UMN).

Varieties (4)

Wisconsin Horticulture names 3 cultivars of Sprenger's asparagus; NC State lists no cultivars of the plumosa fern, which is sold as the species.

Pests to watch for

Aphids, Mealybugs, Twospotted spider mite, Whiteflies, Slugs

Diseases and problems

Root and crown rot, Leaf spot

In the kitchen

Safety: The berries are poisonous: eating them can cause stomach pain, vomiting and diarrhea, and the sap can cause a skin rash, so wear gloves (NC State rates it medium severity; the toxins are sapogenins). The stems carry sharp spines, and this is not the edible garden asparagus.

Pets: Toxic to dogs and cats (ASPCA, listed as asparagus fern, A. densiflorus 'Sprengeri'): eating the berries can cause vomiting, abdominal pain and diarrhea, and repeated skin contact can cause allergic dermatitis. The ASPCA doesn't name the toxin; NC State lists sapogenins.