Aglaonema

A moderate, steady feed with micronutrients, copper above all, and far less indoors. Salt, not hunger, burns the tips.

Florida growers feed with controlled-release or soluble fertilizers carrying micronutrients, in a 3:1:2 ratio of nitrogen, phosphate and potash, at 2–2.5 lb of nitrogen per 1,000 square feet a month (about 10–12 g per square meter) or 150–200 ppm nitrogen in a soluble feed. Most cultivars are prone to copper deficiency, which turns the newest leaves chlorotic, sometimes dwarfed and deformed; the remedy is copper sulfate on the soil or copper sprays, and soil kept above 65 °F (18 °C), since roots take up copper poorly from cold soil. The root zone is checked every two or three weeks by the pour-through method: a soluble-salts reading of 1 dS/m means the plant will go short unless it is fed, 2 dS/m is adequate, and 3 dS/m or more calls for less fertilizer or a leaching.

More is not better. Conover and Poole found that doubling the fertilizer for ‘Fransher’ from 1,500 lb of nitrogen per acre a year added basal shoots but no other growth, and judged that even the lower rate may be more than necessary. Indoors the guide suggests a 20-20-20 soluble fertilizer at 50 ppm nitrogen once a month, warning that overfeeding builds up salts that injure the leaf tips and margins. The RHS gives a balanced liquid fertilizer monthly in the growing season, and Gilman rates the plant’s salt tolerance poor.

Shade, warmth above 60 °F (16 °C) and an even regime. The plants live in rooms too dim for most foliage plants, but a chill below 55 °F (13 °C) marks many cultivars with greasy patches.

Light

Florida growers produce the crop under 75–90% shade, 1,250–3,000 foot-candles (about 13,000–32,000 lux), most of them at 80–90%, because toward the bright end the leaves lose color and stand upright; badly bleached leaves may not fully recover. Indoors the plants tolerate as little as 25 foot-candles (about 270 lux) but never full sun, which scorches them. Gilman finds that they do well in conditions too dark for most tropical plants, and outdoors in USDA zones 10B–11 he puts them on the north side of buildings or under heavy tree shade, since direct sun turns the leaves yellow.

Warmth and chilling

Chilling is the genus’s weakness. UF/IFAS describes injury at anything from just above freezing to 59 °F (15 °C): two days after the chill, dark, greasy-looking patches appear between the midrib and the margin, and a leaf with more than half its area damaged may yellow and fall. Mature and old leaves suffer, young ones hardly at all, and cultivars differ widely. After 24 hours at 35 °F (2 °C), ‘Silver Queen’ had 68% of its leaves injured, and 30% even at 55 °F (13 °C), while ‘Emerald Star’, ‘Stars’ and ‘Jewel of India’ were untouched. For sensitive cultivars the guide keeps greenhouses above 60 °F (16 °C). ‘Silver Queen’ still dominated the market 30 years after its introduction, Hull and Henny wrote in 1995, but its sensitivity limited its production in south Florida, where growers did not want the added expense of winter heating. Eric Schmidt of Harry P. Leu Gardens in Orlando, Florida (USDA zone 9b/10a), wrote to the Aroid-L mailing list on July 7th, 2006, that ‘Alumina’ is one of the hardier Aglaonema, tolerating temperatures down to about freezing, and on August 14th, 2006, that ‘Queen of Siam’, a plant at the garden, is another, tolerating down into the low 30s °F (about 0 °C). The RHS rates Aglaonema modestum H1b, a plant for a minimum of 10–15 °C (50–59 °F).

Air and water

In the forest the genus belongs to the mesophytes, which Boyce and Wong describe as intolerant of atmospheric dryness, dry roots and direct sun, among the first plants to die out when a forest is heavily disturbed; in a pot, the Florida researchers count tolerance of low humidity among its virtues. NC State finds that it prefers high humidity but tolerates drier air, though the leaves brown in very dry air or a draft, and the RHS mists Aglaonema modestum daily. The medium is kept moist but not saturated; Gilman lets it dry slightly between waterings, but not for more than a few days. Steadiness matters: the Florida guide blames a new leaf emerging with a bent, fishhook-like tip on fluctuating light, feeding, water or temperature.

Flowering on demand

The Florida guide removes inflorescences as they appear, to keep the plant full and long-lived. Breeders need the opposite. Under natural conditions, Henny and colleagues wrote, a stem produces only three to five inflorescences a year, and in Henny’s collection plants of one cultivar grown together did not always flower at the same time. In December 1981 Henny sprayed ‘Treubii’ once with gibberellic acid at 100–400 ppm; every treated plant opened its first inflorescence within 148 days, with normal flowers and viable pollen, while only one untreated plant flowered. A single 250 ppm spray then brought several species and hybrids into flower together within five months, so that they could be crossed for the first time; plants sprayed on November 10th, 1982 flowered from mid-April into July, some pots of three or four stems producing upwards of 50 inflorescences, a heavier flowering than the spray normally gives. In Taiwan, Yeh and colleagues had plants flowering 23–48 weeks after one such spray.

Cuttings and suckers in the trade, tissue culture with difficulty, seed for the breeders. The older hybrid cultivars come from crosses made in Florida in the 1960s, and leaf patterns follow simple rules.

Cuttings, suckers and tissue culture

Commercial plants start almost entirely from cuttings, Yeh and colleagues wrote in 2007. The Florida guide roots cuttings with four or five leaves and divides the basal shoots, or suckers, of which cultivars make anything from more than four to none. Henny added cane cuttings and, for cultivars of Aglaonema commutatum, naturally apomictic seed; the RHS separates basal shoots with three or four leaves and roots attached, in spring. Tissue culture had little success with this genus, mainly because of microbes living inside the tissues, and in 1995 Hull and Henny named it as the brake on introducing new cultivars. Yeh and colleagues proposed a way around it: pieces of female flowers cultured with dicamba and thidiazuron gave shoots with neither contamination nor browning, which, they wrote, promised several plants from one inflorescence without significant damage to the mother plant.

Seed and breeding

Henny’s first attempts at crossing were largely unsuccessful until he found that humidity governs the pollen. Inflorescences of ‘Chartreuse Halo’, Aglaonema pictum and ‘Treubii’ kept at 100% relative humidity for 24 hours after pollination germinated their pollen well, those at 50% poorly; each pollinated spadix has since been wrapped in damp paper towel inside a plastic bag for a day, and seed failures became rare. Because the female flowers are receptive two days before the pollen appears, no emasculation is needed; pollen is brushed from another inflorescence and used fresh, since it keeps only a day or two. The seed ripens in four to six months, its fleshy covering turning bright red, and is cleaned and sown at once, before it dries, at about 80 °F (27 °C). Peter Boyce, in a seed-sowing note to the Aroid-L mailing list on April 9th, 2004, gave the germination time as four to six or more weeks at 70–84 °F (21–29 °C) for Aglaonema seed sown covered to its own depth. A first leaf takes eight to ten weeks, and a seedling needs at least a year to reach a size worth judging, though a hybrid shows its mature leaf pattern in its first leaf.

Where the cultivars come from

The four hybrids among the older cultivars, Henny wrote, were ‘Silver Queen’, raised by Bob McColley of Bamboo Nursery in Orlando, and ‘Silver King’, ‘Parrot Jungle’ and ‘Fransher’, raised by Nat DeLeon of Miami. Henny thought ‘Silver Queen’, ‘Silver King’ and ‘Parrot Jungle’ most likely all came from Aglaonema commutatum ‘Treubii’ × Aglaonema nitidum ‘Curtisii’, though a selection of Aglaonema pictum was reported as a parent of two of them, and Nicolson had already suspected that some reported hybrid origins were simply apomixis. The Florida guide of 2003 counted 29 Aglaonema hybrids that received US patents during the 1990s. Breeders, Henny and colleagues wrote in 2009, commonly crossed Aglaonema nitidum, Aglaonema commutatum, Aglaonema costatum and Aglaonema rotundum, for new leaf patterns and petiole colors, more branching and better resistance to chilling; the University of Florida’s ‘Diamond Bay’ and ‘Emerald Bay’ were selected from mutations of ‘Silver Bay’ and ‘Golden Bay’ in tissue culture.

The leaf patterns follow simple rules. Henny found variegation dominant over plain green and each pattern controlled by its own allele of a single gene; the alleles are codominant, so a seedling can show two patterns superimposed on one leaf, but never more than two. Petiole color is more complicated, but by Henny’s guidelines a pink petiole appears only when one parent has it and the other a pink, russet or white one, never from a cross with a green-petioled parent.

A short list of insects, a root rot first noticed in Florida nurseries in 1943, and a set of troubles that are not pests at all. The sap can irritate, and the ASPCA lists the plant as toxic to pets.

NC State Extension names aphids, mealybugs, spider mites and scale, armored or soft; the RHS warns of mealybugs in the leaf axils; and Gilman adds soil-borne nematodes and mites.

The serious trouble is root rot. Pythium splendens root rot was first noticed in nurseries in Orange County, Florida, in 1943, on Aglaonema modestum. Over about three weeks the plants are stunted and droop, then rot off at ground level and fall over; other aroids suffered less. In Miller’s trials of 1959, beds of Chinese evergreen planted in infested peat lost 87.4% of their plants untreated, against at most 1.27% after the soil was fumigated. Leaf spots caused by anthracnose fungi have been recorded as well. The growing guides’ defense is prevention: a mix allowed to dry between waterings, cuttings inspected on arrival, since shipping can spread disease, and propagation containers kept off the ground.

Several complaints are not pests: in the Florida guide’s table, dark, greasy patches are chilling, upright, washed-out leaves too much light or heat, deformed chlorotic new leaves copper deficiency, and brown tips salt. The plant is also not to be eaten. The ASPCA lists Chinese evergreen, Aglaonema modestum, as toxic to dogs, cats and horses: its insoluble calcium oxalates cause oral irritation, pain and swelling of the mouth, tongue and lips, excessive drooling, vomiting (not in horses) and difficulty swallowing. NC State rates the genus low in severity but notes that the sap can cause contact dermatitis, and the RHS calls it harmful if eaten and a skin and eye irritant, to be handled in gloves.