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|Roy Herold's Arisaema Pages Archive is hosted by the International Aroid Society|
By Jim McClements (not necessarily applicable to tropical species)
- Growing conditions
- Shade: While many species in the wild may grow in full or partial sun at high altitudes, in most gardening situations arisaemas should be considered plants for at least partial shade. Bright light without leaf burning is ideal. The warmer the climate in which one gardens, the more shade becomes a necessity, as is true of many other genera. If you live in a cool climate, full sun may work well.
- Cold hardiness: This is still being worked out for the individual species. Suffice it to say that most of the non-tropical species are winter-hardy at least to USDA Zone 6.(minimum winter temp -10 F, -23C) Species from Taiwan and other warmer parts of Asia seem to vary according to their provenance, those from higher altitudes having greater tolerance for cold. Survival in winter may well depend on depth of planting. Arisaemas are often found deep in the ground in nature, and planting in the garden below the expected frost line (perhaps down to 18") can certainly add to winter hardiness, as can snow cover or heavy mulching. However, the deeper the planting, the more one needs to be concerned about good drainage, since winter wet can cause rotting of the dormant tubers. Questionably hardy species can always be lifted and stored in the refrigerator during winter (see paragraph D below).
- Summer heat tolerance: This does not appear to be a problem with any species currently in cultivation. However, excessive drying during summer heat may hasten dormancy, which makes arisaemas slower to increase in size and to flower. "Winter heat intolerance" (winters too warm to allow for a normal dormancy period) may be the limiting factor in how far south most species may be grown.
- Spring frost tolerance: Some of the Japanese species, such as A. sikokianum and A. ringens, which tend to appear very early in the season, are subject to damage by late frosts, particularly if flowers have emerged.
- Soil requirements: neutral or slightly acid pH seems to work well. Drainage very important to prevent rotting of tubers. Raised beds, added gravel, turface (calcined clay) or other soil aerators seem to help.
- Fertilizing: Arisaemas seem to respond well to feeding. It's probably best to feed small amounts frequently or to use a slow-release fertilizer.
- Diseases, Pests
Not eaten by most animals because of high oxalate content in tubers.
Biggest threat is probably "Rust", a fungal disease manifested by yellowish-orange spots on the leaves and spathe, and very difficult to control once it appears.
- Vegetative: some species produce offsets readily, which can be detached from the parent. In some (e.g. A. candidissimum) the small tubers are found already detached. Other species are moderately stoloniferous (e.g. A. ciliatum, A. exappendiculatum).
- Seed: Most species are dioecious (unisex) and only the female produces seed. Therefore, usually a male and female plant are needed to make fertile seed. This is further complicated by the fact that the plants can, and do, change sex. Young plants are invariably male and become female as they get older and more robust, sometimes going through a monoecious (bisexual) stage in the transition. A few species (e.g. flavum, tortuosum) remain monoecious, although not usually self fertile.
The berry containing the seed produces a germination-inhibitor which in nature disappears over the winter, allowing spring germination. However, the seed of most species does NOT require a cold period to germinate, and if the seed is cleansed of the inhibitor (30 minutes in a detergent solution works nicely) it will usually germinate promptly. It appears that at least two species DO require a cold period to produce top growth, namely A. elephas and A. thunbergii, and there are probably others.
Since arisaemas take 3 to 4 years to reach flowering size, many of us who grow them try to compress the seasons by "artificial winters". If fresh seed are cleansed and germinated and allowed to grow on to their first dormancy, the small tubers can be collected and stored in a refrigerator at 35-40F for one to three months (there is some disagreement about how long a period is necessary or advisable), keeping them slightly moist in any of several ways. Too much moisture will cause rot, but small tubers won't tolerate being dry as well as larger ones do. They are then replanted and emerge in a few weeks for their second growing season in one year's time. If the one month "winter" proves to be sufficient, it may be possible to get close to three seasons in one year.
- Pot Cultivation If arisaema are grown in pots, it is suggested that the pot diameter be at least four to five times the diameter of the tuber. Fertilization and watering need to be more carefully monitored than for garden grown plants. Winter storage must also be watched carefully. Tubers will not usually tolerate being frozen through. Since yearly repotting is advised, unpotting the tubers and storing them in a slightly damp peat mixture in a refrigerator bag, at 35-40 degees F, may be the best idea.
Arisaema Seed Starting, Method #1
by Ellen Hornig
I am writing this from my own experience of germinating approximately 25 species of Arisaema, almost all of which seem to respond in a similar fashion to the conditions I give them. I have not conducted many experiments, and so cannot compare my methods with others. I can only report that what I do is simple, and works.
Both fresh and dry Arisaema seeds germinate easily, and at fairly high rates (75 to 100 percent). The first leaf typically appears between 4 and 8 weeks from sowing, though some species appear sooner (A.flavum), and some will produce only a corm in the first season, with the first leaf emerging, after dormancy, in the second period of growth. In only one case have I had germination (as opposed to leaf production) delayed at length (A. limbatum), approximately 14 months). However, there are many species I have not yet tried.
I start my Arisaem seeds under standard fluorescent fixtures using inexpensive cool-white bulbs. The fixtures are on timers and are set to 14 hour days. Because the fixtures are in a cool basement, with winter temperatures typically around 13C, I drape and staple polyethylene sheeting over the fixtures to trap some heat (and humidity) inside. This raises the surface temperature of the pots to around 21C while the lights are on. I have not found it necessary to provide bottom heat.
A. Seed Preparation
If fresh seed heads or berries are available, remove the seeds from the pulp (wear latex gloves while doing this, or your fingers will burn for days) and rinse in several changes of water until the seeds are clean. They are then ready for sowing.
find it helpful to soak dry seeds for approximately 48 hours (with several changes of water during that time) before sowing. Anecdotal evidence suggests that soaked seeds germinate 2 to 4 weeks ahead of unsoaked seeds.
B. Germination mix
The mix must be free-draining; soggy conditions promote rot. I use three parts Fafard Super- Fine Germinating Mix to one part granite chick (starter) grit. The Fafard mix contains peat moss, vermiculite, perlite, and a starter charge of fertilizer.
Although I use Kord nine cm pots for everything (because they fit neatly, 18 to a 25 cm by 51 cm tray, and I sow a lot of seeds), a deeper and narrower pot might be preferred. The nine cm pot works well as long as the mix drains freely; a deeper pot would simply promote even freer drainage.
I fill the pots and water the mix to settle it (the surface of the mix should be approximately two cm below the top of the pot). After the pots drain, the seeds are sowed on the surface of the mix and sprayed lightly with water to ensure proper contact with the mix. The surface is then covered with approximately one cm of chick (starter) grit. If I am starting large numbers of pots at the same time, I saturate the pot surfaces with a Captan spray to prevent damping-off.
I often sow 25 to 50 seeds in a nine cm pot, but that would be too many if the corms were going to be grown on in the same pot for another year. I prefer to crowd them at first and separate them later (during their first dormancy).
E. Growing On
The pots are then placed under lights, as described above, and more or less left alone, except that surface moisture should be checked every few days and replenished as necessary. It is very important that germinating seeds never dry out. I prefer surface watering, on the theory that it is less likely to saturate the bottom of the pot and create future problems.
Once leaves emerge, I fertilize from time to time with one quarter strength Miracle-Gro or equivalent. I try to keep the medium evenly moist as the leaves develop; once they are completely unfurled, they will tolerate slight drying, but excessive drying may send them into a premature dormancy.
Once the leaves are fully unfurled on all of the seedlings (and remember that seedlings may continue to emerge over a two to three week period) I remove the pots from the warm poly tents and set them under uncovered lights to grow on. I find the cooler temperatures promote more compact growth and, of course, reduce the likelihood of fungal infections.
At this point, the objective is simply to keep the leaf active and photosynthesizing for as long as possible, in order to build up as large a corm as possible before dormancy sets in.
F. First Dormancy
When the leaves on your seedlings begin to fade, yellow, and collapse, the seedlings are going dormant. At this point, cease most watering (try to keep the medium very slightly damp, but too dry is far less harmful than too wet). If you have started the seeds indoors during the winter, dormancy may well occur by early summer. Simply let the pots sit, preferably in warm and dryish conditions (i.e. in a shady outdoor location) until fall. You may find that some corms resume growth towards late summer; A. jacquemontii has a strong tendency to do this. If they do, resume watering and fertilizing and provide adequate light. Otherwise, when the weather gets cold, bring the dormant corms inside. This is a good time to empty out the pots and admire your handiwork; the corms can now be repotted (perhaps 12 to 16 to a 10 cm pot) in a more nutritious but still well-drained mix (I use Metromix 510 with perlite added, but haven't measured the proportions). As an alternative, they may be mixed with slightly damp peat moss and kept in polyethylene sandwich bags in the vegetable drawer of the refrigerator. If you choose to pot them up, water them thoroughly once and set them in a cool place (I use the coldest corner of the basement); thereafter, water only enough to prevent them from drying completely.
Corms of different species emerge from dormancy at very different times, so you should begin checking your dormant corms as early as December if they've gone dormant in June. As soon as new growth is detected, pot up (if in baggies), water, and move to a well-lit position.
I have little experience with this, but many people like to push the development of Arisaema by shifting newly-dormant corms immediately to cold conditions (the refrigerator), holding them there three months, and shifting them back to warmer conditions.
Arisaema Seed Starting, Method #2
By Jim McClements
I start all my Arisaema seeds as follows:
- Clean the pulp off, if not already done.
- Soak seeds in a glass of water, with a few drops of "Dawn" detergent added, for an hour or so (I've left some in overnite with no apparent ill effects).
- Place seeds in a moist, folded white paper towel, ala Deno, and put in a warm closet.
- Check every 2-3 days and when a few of the seeds in the towel show a radicle, plant all those seeds.
- I plant them in wet turface, in standing water, under lights. When the seedlings put up an eophyll, I move the pot to a different flat and begin adding a VERY dilute solution of balanced fertilizer to the standing water. The seedlings are grown on this way for 3-4 months until they start to brown and go dormant.
- When dormant, the pot is allowed to dry off for a few days, the small tubers are harvested from the turface (which is very easy if you dump the pot into a bowl, add a little water and see even the tiniest tubers floating), and are refrigerated in a "baggie" in damp Promix. Shouldn't be wet, but the smaller the tuber, the more moisture needed. With small tubers there seems to be more danger of drying up than rotting.
- After 2-3 months in the fridge, they are replanted, this time in a promix-turface mixture with a grit top-dressing, and start their second season. Don't use Osmocote in the mix! And go easy on the water until the plant re-emerges, or the tubers will rot. The mix will stay damp for quite a while under the grit top-dressing. It generally takes from one to three months for re-emergence.
- Transfer to the garden, or do another "artificial winter" after the second growth period, depending on size, time of year, etc. Back to the towels. If seeds get moldy and soft, they were probably not viable in the first place. If they look OK but don't show a radicle in 3 months at room temperature, they may well be one of the species that need one, or even two, cold periods before germinating. Those seeds are refrigerated in the towel/baggie combo, brought out again in 3 months for another stay in the closet.