Asparagus fern

Identification and origin

Asparagus setaceus belongs to the family Asparagaceae, the same family as garden asparagus, so it is not a fern at all despite its common names. It is native to a wide area of Africa that runs from central Ethiopia through Kenya, Tanzania, and Mozambique down to South Africa, Lesotho, and Eswatini, as well as the Comoros.

It is an evergreen perennial that starts out bushy and then climbs. Its thin, wiry stems, which turn woody with age, carry sharp spines and twine around any support within reach. What look like leaves are actually cladodes: tiny green branchlets, needle-fine and soft to the touch, that carry out photosynthesis. The true leaves are reduced to small dry scales. The branches spread in flat horizontal tiers that get shorter toward the tip, creating the distinctive triangular plumes.

In the wild the plant can climb to 10–19.5 ft. In a container it usually reaches 2–3 ft tall and about as wide. In summer it sometimes produces tiny white flowers, rare indoors, followed by berries 0–0 in across that ripen from green to dark purple or black; birds spread the seeds. Underground it forms thick tuberous roots that act as a reserve.

The genus name comes from Greek and refers to plants that send up edible shoots from their rootstock; the epithet setaceus means “bristly.” Widely used by florists to fill out bouquets, the plant has escaped from cultivation in several warm regions: it is considered invasive in Australia, New Zealand, Cuba, and Hawaii, and it needs to be managed in Florida. In a frost-free climate, avoid planting it in the ground.

Light

Give it bright but indirect light, for example near a bright window behind a sheer curtain. Direct sun, especially during the hottest hours, does it harm and scorches the delicate foliage; it copes better with light shade than with too much light. If it summers outdoors, keep it in part shade or under the dappled shade of a tree.

Watch the cladodes: too little light, like too little water, makes them turn yellow and drop. Damaged branches do not green up again, but once conditions are corrected, new shoots emerge at the soil line.

Watering

From spring through fall, water generously as soon as the surface of the potting mix starts to dry, then empty the saucer: the root ball should stay evenly moist but never sit in water. In winter, water much less often and let the surface dry a little more between waterings.

Watch the plant rather than the calendar. Needles turning yellow can mean a long dry spell just as easily as too much water or poor drainage, so always feel the mix before acting. The thick storage roots help the plant ride out an occasional missed watering, but watering too often rots the roots.

Asparagus fern likes humid air. Tips turning brown often point to air that is too dry, especially while the heat is on: set the pot on a tray of moist pebbles or run a humidifier.

Potting mix

Choose a mix rich in organic matter that holds moisture yet drains well, preferably a peat-free, loam-based one. A slightly acidic to neutral pH suits it. The pot must always have drainage holes.

Temperature

The plant is happiest between 55–70 °F. It is not hardy: it tolerates some coolness, but frost kills it. If you move it outdoors for the summer, bring it back inside as soon as temperatures drop toward 55 °F. It can only be grown in the ground in USDA zones 9a to 12b.

Repotting

The thick tuberous roots fill a pot quickly. Repot in spring into a slightly larger container as soon as the root ball is packed with roots. If you let the stems climb, give them something to hold on to: a stake, a trellis, or taut wires.

Pruning

No pruning is needed. To keep a tidy shape, pinch back stems that grow too long; this encourages new shoots. If a stem is damaged, yellowing, or bare, cut it off completely at the base rather than just shortening it. Wear gloves: the spines are sharp and the sap can irritate the skin.

Propagation

Division is the easiest method. In early spring, at repotting time, slide the plant out of its pot, split the root ball into several sections that each keep some stems and part of the tuberous roots, and pot them up separately in fresh mix. Keep them out of direct sun and water moderately until they settle in.

It can also be grown from seed in fall or early spring. Sow in a tray and keep it at about 61 °F for germination, with the mix lightly moist. Collect the berries only while wearing gloves, and keep them away from children and pets.

The cultivar ‘Pyramidalis’ has a more upright, pyramidal habit, with vertical triangular plumes 16 in – 2 ft long; it stays somewhat more compact than the climbing forms.

Common problems

• Yellow needles that drop: too little light, too little water, or the opposite, too much water and poor drainage.
• Brown tips: air that is too dry.
• Root rot: watering too often, a saucer left full, a pot without drainage holes.
• Spots on the foliage: poor air circulation and wet foliage.
• Pests: mealybugs, spider mites, and aphids indoors; slugs, snails, and asparagus beetles outdoors. Check the base of the branches regularly.

The same symptom can have several causes: always look at light, watering, air humidity, and the condition of the roots together before making changes.

Toxicity

Toxic to dogs, cats, and horses, and to people as well. The berries contain sapogenins: eating them causes digestive upset (vomiting, abdominal pain, diarrhea). Repeated contact with the plant can trigger allergic dermatitis, the sap irritates the skin, and the spines can injure. Handle it with gloves, keep it out of reach of children and pets, and if any part is swallowed, contact a veterinarian or a poison control center.