What's Wrong with My Canna Lily?

The Brazilian skipper butterfly lays eggs on canna foliage and the caterpillars roll the long, paddle-shaped leaves lengthwise and sew the edges shut with silk to feed inside. Because canna leaves emerge rolled from the stalk, the pest is often hidden until you see the silken seam along the edge or the jagged chewing damage when the leaf finally unfurls.

Cannas evolved in open tropical and subtropical clearings and need a minimum of 6 hours of direct sun to produce their large showy flowers. In part shade, the plant puts all its energy into the tall, leafy stalks and skips flowering entirely. The foliage may look lush and healthy while producing zero blooms.

Canna rhizomes spread aggressively underground and after 2 to 3 years a clump becomes so dense that the plants compete with each other for nutrients and space. Crowding slows flowering noticeably. Poor soil or skipped fertilizer has the same effect since cannas are heavy feeders that need regular nutrition to power their tall stalks and large blooms.

Cannas are big plants with big appetites. Their large leaves and rapid vertical growth burn through nitrogen and potassium quickly, especially in sandy soil or after heavy rain flushes nutrients away. Yellowing that starts on older leaves and moves inward toward newer growth is the classic sign of nitrogen running low.

Cannas love water but cannot tolerate sitting in soggy, poorly drained soil. Their thick rhizomes begin to rot when the soil stays saturated, cutting off the nutrient supply from below. Yellowing in waterlogged conditions affects the whole plant at once rather than progressing leaf by leaf.

Canna rust is a fungal disease that shows up as small orange or rust-colored pustules on the undersides of leaves, with yellow patches on the top surface directly above. The large, broad canna leaves hold humidity and morning dew close to their surface, giving the rust fungus ideal conditions to spread in warm, moist weather.

Slugs target the soft, tender emerging shoots and young canna leaves, eating irregular holes overnight and leaving a slime trail behind. Because new canna shoots push up from rhizomes at soil level, they are easy targets before they have a chance to grow out of reach. Damage is worst in cool, damp conditions and in mulched beds where slugs hide by day.

In zones 6 and colder, canna rhizomes are dug up in fall and stored indoors over winter. Rhizomes are dense, moisture-rich structures that rot quickly if stored damp or in temperatures below about 45 degrees Fahrenheit. Even a short cold snap in an uninsulated garage can turn a healthy rhizome to mush before spring.