By fall, some mature plants will also offer a cluster of showy red berries that become more visible after the spathe withers away. The berries shine brightly and will add considerable luster to your shade garden late in the growing season. Jack-in-the-pulpit is a slow-growing perennial that is usually planted from corm-like roots in the fall, or potted nursery plants in the spring. Be aware that this plant contains oxalate crystals and is very toxic to people and animals if consumed. Eating it can cause extreme pain and swelling of the mouth and digestive tract. To plant, make a 6-inch hole in the ground in the fall and drop in the corm-like root, as you would do if you were planting a crocus. Once the plants have come up in spring and put on some size, shovel 2 to 3 inches of mulch around them to conserve moisture. The three-part compound leaf of bog onion may remind you of poison ivy (Toxicodendron radicans). The leaf structure also resembles that of trillium which shares the same native habitat.
Light
Some shade is an absolute must for Jack-in-the-pulpit. The plant performs well even in deep shade. Avoid too much direct sunlight at all costs.
Soil
These wildflowers do not demand the superb drainage that many plants do, making them an option for boggy soils. The idea is to mimic the native habitat, which is damp, acidic areas of the forest that are rich in organic matter.
Water
Evenly moist soil is another must for growing Jack-in-the-pulpit.
Temperature and Humidity
Jack-in-the-pulpit is reliably hardy in zones 4a to 9a, provided it gets the damp, humid conditions it craves. Try to provide the moist, boggy environment that gives the plant one of its common names—bog onion. During the growing season, it likes moderate conditions that avoid temperature extremes.
Fertilizer
Fertilizing with compost is sufficient in most cases. But you can use an acidifying fertilizer if necessary to lower the pH of alkaline soils into the acidic range these plants favor.
Types of Jack-in-the-Pulpit
The various types of Jack-in-the-pulpit are usually regarded as subspecies of the same plant, although some experts view them as separate species. The differences are fairly minor and gardeners usually have little reason to be concerned about which type is being offered. Commercial growers often neglect to even specify the subspecies: Arisaema triphyllum. subs. pusillum, Arisaema triphyllum. subs. stewardsonii, or Arisaema triphyllum subs. quinatum. In addition, there are several other species in the genus that may be sold commercially as Jack-in-the-Pulpit but are a different species from Asia commonly called cobra lilies.
‘Arisaema consanguineum’ has purplish with light green stripes, ending in a long “tongue” that makes it look like a cobra’s head. This plant is a native of the Himalayas.‘Arisaema saxatile’ has a long tongue, but in this case, the tongue is the spadix and the spathe is white. This plant is native to China.‘Arisaema griffithii’ offers an elaborate light-green veining pattern at the top. It is commonly known as Griffith’s cobra lily. It is a native of the Himalayan region of India.
How to Propagate Jack-in-the-Pulpit
The quickest way to propagate new plants is by splitting off the cormlets that form alongside the parent roots. Here’s how to do it:
How to Grow Jack-in-the-Pulpit From Seed
Jack-in-the-pulpit seeds need to be cold-stratified to germinate. This means keeping them damp in sphagnum moss, in a refrigerator, for at least 60 days. Then, sow them in a flat filled with soilless commercial potting mix and keep the flat in a cool, damp place. Germination should take two to three weeks. Continue growing seedlings in the flat for two years before transplanting them into individual pots or into the garden. Correct watering is critical, as too much water will cause the seedlings to rot, while too little will also kill them. Started from seed, Jack-in-the-pulpit will require as much as five years before they reach flowering maturity.
Overwintering
Don’t feel compelled to clean up fallen leaves and plant debris from the area where Jack-in-the-pulpit is growing. This decaying material is essential to providing the plant with the nutrients and soil moisture it needs. Jack-in-the-pulpit is perfectly hardy in its established range (zones 4a to 9a) and requires no protection against winter cold.
Common Pests & Plant Diseases
While not a destination for most pests and diseases, Jack-in-the-pulpit is a favorite for slugs. This is easily remedied by placing a small dish of beer in your garden and letting the slugs crawl in for a drink.
How to Get Jack-in-the-Pulpit to Bloom
Be patient. This plant may take as much as four or five years before it is mature enough to bloom. If mature plants refuse to flower, it may be for one of the following reasons:
Too much sun: These plants absolutely require shade. If they receive more than a few hours of daily sunlight, they will be reluctant to bloom at all.Barren, dry soil: These plants like porous, rich, humusy soil such as is found in damp woodland settings. Dense clay or dry soil will prevent them from blooming.
Common Problems With Jack-in-the-Pulpit
Most problems with Jack-in-the-pulpit arise because gardeners have trouble providing it with the consistent moisture it needs. Dry conditions will quickly cause the plant to go dormant, often before the plant has a chance to flower. Make sure your Jack-in-the-pulpit plants are getting enough water and are properly mulched to maintain soil moisture. This is not a plant well-suited to dry shade—it wants a dampish environment, such as that found in low-lying, boggy areas of a rainy forest floor.
