How to Plant, Grow, and Care for Crinum Lily

Crinum lily plants are poisonous. In fact, while they’re largely known as spider lilies, they’re also called poison bulb. I’m guessing you’re wondering why you’d want to grow a poisonous plant. The answer’s simple: because they’re stunning.

These plants reach heights of four to six feet, with long, slender blade-like leaves. Their flowers are usually white but may have red or purple highlights. They thrive in subtropical temperatures. In fact, they’ve become naturalized in much of the southwestern United States.

If you’re in a warm climate, you’ve probably seen these before. Follow this guide to learn how to grow them in your own backyard.

What is Crinum Lily?

Crinum lilies originate from Asia, Australia, and the Pacific and Indian Ocean islands. These subtropical plants can tolerate cooler climates but thrive in warmth. This likely explains why they’re so popular in parts of southern California.

The flowers are reminiscent of stars. Each long, tubular flower has six petals that extend out to the sides. Most of the time they are white in hue, but they may develop reddish stripes or a purplish tint. These flowers are massive, growing to sizes of four inches long and wide. Long filament-like stamens in a reddish hue protrude from the flower’s center.

Crinum flowers grow on a long scape that extends high above the long, sword-like leaves. Up to 25 or 30 flowers can form on each scape, making for a huge cluster of brightness amongst your foliage.

Leaves can reach four feet in length and up to five inches wide near their base. Generally, they remain narrow in comparison to their length. These develop in a cluster at the base of the plant, and it’s from this dense foliage that the flower scapes erupt.

As for the bulb of the poison bulb plant, it’s as massive as all other aspects of this lush subtropical. A typical bulb can be 10-25 pounds! They take up a massive amount of space under the ground. From the bulb’s tapered neck is where the foliage grows.

Planting

These bulbs are typically planted from April to October in the Northern Hemisphere. Choose a location in your garden that receives at least six hours of direct sunlight daily. The soil should be well-draining, as crinum lilies do not like to sit in waterlogged soil.

If your garden soil tends to retain water, consider planting them in raised beds or amending the soil with sand and compost to improve drainage.

Loosen the soil to a depth of about 12 inches. Mix in a generous amount of organic matter, such as compost, to enrich the soil. Crinum lily bulbs are large, so dig holes about 10 inches deep and wide enough to accommodate the bulb comfortably. Place the bulb in the hole with the pointed end facing upward and the roots facing downward.

After planting, water thoroughly to settle the soil and help the roots establish. Mulching around the plants with a two or three-inch layer of organic mulch helps retain soil moisture and suppress weeds.

How to Grow

These magnificent and large plants can be a bold addition to your landscape. But, like all subtropicals, they have specific preferences. Let’s go over what the crinum lily needs to survive.

Light

Spider lily loves the sun. But it’ll accept partial shade, particularly if it’s during the hottest part of the day. It can develop leaf scorch if the intensity of the sun is too harsh.

Most people will find that six to eight hours of sunlight is perfect for optimal growth. If you’re in a particularly hot climate, consider four to six hours of direct sun and a couple of hours in partial shade.

Water

These plants love moist soil. Pond borders and poolside placements are common. But don’t limit them to those areas. If you water regularly, you can place these throughout your yard.

While the crinum lily can tolerate infrequent watering, they won’t grow as fast. Short periods of drought are okay, as long as they don’t last more than a few days to a week at most. These bulbs may need more water during the hottest times of the year.

At the same time, don’t overwater. If there are puddles or the ground is muddy, wait for the water to drain away and the soil to partially dry. Excess water can cause the bulb to develop rot.

Soil

Your ideal soil for your spider lily plant should be moist but well-draining. It should be rich with organic matter and fertile. While this plant can grow in poor soils as well, it will be vigorous with this mix. I like to use a sandy soil base and amend it with lots of compost.

I recommend adding shredded leaf mulch or wood chip mulch around the base of plants. Not only will this continue to improve the soil quality, but it will also prevent evaporation.

Temperature & Humidity

In cooler climates, this plant should be brought indoors before cooler weather arrives. Once the temperature dips below 40F at night, you run the risk of the leaves becoming cold-damaged.

These plants are not frost-hardy at all, and the first frost often causes dieback of foliage.

Fertilizing

For my crinums, I like to use a slow-release, balanced granular fertilizer. Spread this in early spring, early summer, and early fall around the base of plants. Work it lightly into the soil. This should be plenty of food for your plants.

If you’d prefer a liquid, opt for a half-strength liquid fertilizer. From spring through the summer, fertilize monthly. Only fertilize it once early in the fall, and skip the winter entirely.

Maintenance

Your poison bulb plant won’t need much in the way of pruning. But when you do trim it, take precautions. All portions of the plant are poisonous, so wear gloves. Sterilize your pruning tools before and after working with this plant.

Trim off dead leaves or spent flowers. Remember, 20 or more flowers can form on one scape, so be sure all the flowers on the scape are spent before pruning. Then, cut the scape back close to the plant’s base. Another scape will develop from the same location when it next flowers.

If you live in USDA Zone 8 or 9, you may need to prepare your plants for overwintering. This ensures that any frost won’t hurt the plant. Trim back the leaves to the ground as the weather gets cool. Cover the plant with a few inches of mulch to protect the bulb from chilly conditions.

Those who get frosts and freezes throughout the winter should be ready to move indoors. Carefully uproot your bulb and place it in a pot slightly larger than the bulb itself. Fill in around it with soil. Keep it indoors in the brightest area you can find through the chilly months.

It can be really helpful to remove the outermost leaves on bulbs that are moved indoors. This prevents the plant from taking extra space.

Propagation

Crinum lily propagation is through seed or by division.

Seeds are slow to get started and may be unreliable, but it is an option. Plant shallowly, no deeper than an eighth of an inch beneath the soil’s surface. Once they have germinated, remove the weaker ones and keep the strong ones. Allow them to develop some foliage and begin to form a bulb before transplanting into small pots.

Plant your seedling plants outdoors in the spring after all chance of frost has gone. It’s important to harden off your plants to the outdoor conditions before transplanting.

Division is often the simpler option. Loosen the soil around your plant’s base and determine how large the bulb is. Remove it and all attached offshoot bulbs. Be careful not to damage the bulbs. It should be easy to separate the plants by gently untangling roots and separating them.

Once separated, replant in the garden bed, leaving at least two to three feet between the plants. They will grow to fill in the space. You can also place smaller offshoot bulbs into pots. They prefer to become rootbound in the pot, so use a pot that is just slightly larger than the bulb itself.

When planting offshoot bulbs or replanting your older ones, bury all but the top of the neck under the soil. Leave the neck poking up over the soil’s surface. It’s from that neck that your plant will form.

Common Problems

One great thing about these plants is that they are tough. They cling to life regardless of the situation they’re in. Poor soil, occasional drought, or bad temperature conditions may cause damage, but they’ll often recover.

There are still a few things you will still need to handle if they appear, however.

Leaf Scorch

As mentioned, plants in hot, full-sun conditions can experience leaf scorch. While not common, it does happen when the temperature peaks mid-to-late summer.

If you have a large plant, a few scorched leaves won’t cause you any harm. But if it’s young, this may be a problem. Try to place your plants where there’s afternoon shade if you’re in a hot climate.

Bulb Rot

If over-watered, you may find the bulbs start to rot. They’re tolerant of excess water to a point, but eventually will succumb. Ensure your soil is well-draining to prevent this problem by adding sand or perlite and compost.

Brown Leaves

If the tips of the leaves are starting to go brown, this is usually a sign of too little water. Be sure the moisture in your soil is consistent. Mulching around your plants can help keep the soil moist for longer periods of time.

Pests

Some types of grasshoppers, especially the eastern lubber grasshopper, can become a problem. These hungry little pests will devour the leaves of your plant. To combat these, use a Bacillus thurigiensis (Bt) spray or powder. The grasshoppers won’t survive.

Some types of mealybugs find spider lilies appetizing. A good spraying of neem oil makes for a deterrent. An insecticidal soap may also be useful if they are persistent.

Nematodes, particularly root-knot nematodes, may become a problem. Use beneficial nematodes to counteract these bad forms. The beneficial ones will protect your plants from a host of other problems, too.

Finally, those long leaves are appealing to both slugs and snails. Not only do they provide daytime cover they can hide in, but they taste good too. Apply an organic slug and snail bait around your plants to lure them out and kill them off.

Diseases

Anthracnose leaf spots are not uncommon on these plants. Your best bet to combat these is to use a copper-based fungicide. Sulfur-based fungicides will also work, but to a lesser extent.

Powdery mildew occurs when the weather is warm and humid. It won’t severely injure your plant, but it’s unsightly and annoying and can spread. Neem oil acts as both a preventative and a curative for this issue.

Botrytis cinerea is uncommon but may occur. This is also most prevalent when it’s warm and humid outside. Provide good airflow around your plant and avoid watering from above. If necessary, treat outbreaks with an organic fungicide. Just be careful to vary your methods when fighting botrytis. It’s been known to become resistant to fungicides after repeated use.

Finally, a form of mosaic virus called the crinum mosaic potyvirus may occur. Sometimes referred to as nerine yellow stripe virus, it causes streaked leaves. As of right now, mosaic viruses are incurable. If your plant’s leaves start to develop long, yellowed streaks, remove the plant and destroy it. This prevents the virus from spreading to other plants via pests.

Frequently Asked Questions

Final Thoughts

If you have the space to fit these large bulbs, crinum lilies are well worth planting. Their tall and intricate blooms are bound to stand out in whatever location you choose.