By the time August rolls around, my canna lilies are usually strutting their stuff beside the porch, down by the mailbox, and in the long bed near the vegetable garden where the zinnias and tomatoes keep them company. Here in the Midwest, August can be a make-or-break month for these bold, tropical-looking plants. We get the heat they love, certainly, but we also get dry spells, pounding thunderstorms, tired soil, and the first little hints that the growing season will not last forever. If I want those big leaves glossy and those flowers opening right up until frost nips them black, this is the month I stop admiring and start tending.
Cannas are generous plants, but they do best when someone pays attention. Over the years, I’ve learned that a handful of practical chores in August can mean the difference between a patch that fades early and one that keeps blooming into September and October. These are the 10 tasks I never skip, along with the little details that matter most—how much to water, what to cut, when to feed, and what to watch for when the weather turns sticky and troublesome.
1. Water deeply, not just often
Cannas are thirsty plants, especially in August when daytime temperatures can sit at 85 to 95 degrees for a week straight. Their big leaves lose a lot of moisture, and if the soil dries out too much, bloom production slows first and leaf edges turn brown not long after. I aim to give established cannas about 1 to 1 1/2 inches of water per week from rain or irrigation, and in sandy soil or extreme heat, closer to 2 inches.
The important thing is depth. A quick sprinkle wets only the top inch or two, and canna roots need moisture farther down. I’d rather water thoroughly once or twice a week than splash them every evening. I use a hose at a slow trickle for 20 to 30 minutes per clump, or let a soaker hose run until the soil is moist 6 to 8 inches deep. If the top 2 inches feel dry when I press my finger in, it is time to water again.
2. Feed for flowers, but don’t overdo the nitrogen
August is not the month for heavy, leafy growth at the expense of blooms. If you pour on a high-nitrogen fertilizer now, you may get magnificent foliage and fewer flower spikes. I prefer a bloom-supporting fertilizer with a lower first number, something like 5-10-10 or 10-10-10 used lightly, depending on what your soil already contains.
For in-ground cannas, I usually side-dress each mature clump with about 2 to 4 tablespoons of granular fertilizer, scratched gently into the top inch of soil 6 inches away from the stems, then watered well. For potted cannas, I use a diluted liquid feed at half strength every 10 to 14 days through late August. After that, I taper off so the plants can focus on finishing strong rather than pushing soft, tender growth that cool weather may spoil.
3. Deadhead spent blooms to keep new stalks coming
This is one of the simplest jobs and one of the most rewarding. Each canna flower stalk opens from the bottom upward, with fresh buds forming above older flowers. Once the last flower on a stalk has finished, that stalk will not bloom again. If you leave it standing too long, the plant can put energy into seed production instead of sending up fresh bloom spikes.
I cut spent flower stalks down to the next strong leaf node or all the way to the base if the entire stalk is finished and no side buds remain. I use clean pruners and make a neat cut. Every few days in August, I walk the bed with a bucket in hand, and that little routine keeps the patch tidy and noticeably more floriferous. My mother used to call it “keeping the plant hopeful,” and I still smile at that.
4. Remove yellowing or damaged leaves promptly
By August, even healthy cannas often have a few leaves that are torn by wind, scorched at the edges, or simply aging out. Those leaves do not help the plant much, and they can hide pests and disease problems if left in place. I cut off yellow, brown, or badly shredded leaves close to the stem with sharp pruners.
Be selective, though. Do not strip a plant down because you want it to look “clean.” Those broad green leaves are the plant’s food factory. I remove only leaves that are more than one-third damaged or clearly declining. On a 4- to 6-foot canna, that may mean taking off 1 to 3 leaves per stalk in a week, no more. A neat plant catches more light and airflow, and in my experience it blooms better too.
5. Check for Japanese beetles, caterpillars, and canna leaf rollers
August is prime time for insect trouble in many gardens. Japanese beetles can skeletonize leaves, grasshoppers chew ragged holes, and leaf-rolling caterpillars may glue or fold canna leaves before feeding inside them. If you notice long tears that never unfurl correctly, or leaves stuck together in narrow rolls, inspect closely.
I check my cannas early in the morning, when beetles are slower and easier to knock into a jar of soapy water. For caterpillars or leaf rollers, I remove affected leaves if the damage is limited, or open the rolled section and handpick the pest. In a small home planting, regular inspection every 2 to 3 days often solves the problem before it gets out of hand. Healthy cannas can tolerate a little chewing, but August damage adds up fast when the season is already moving along.
6. Watch for rust, bacterial blight, and overcrowded humidity
Cannas love warmth, but they do not love stale, damp air trapped around crowded leaves. In muggy late summer weather, fungal and bacterial issues can show up quickly. Canna rust often appears as orange to rusty brown pustules on the undersides of leaves, while bacterial blight may cause water-soaked streaks, blackened edges, or collapsing foliage.
If I see diseased leaves, I remove them immediately, bag them, and put them in the trash rather than the compost pile. Then I look hard at my watering habits. Overhead watering late in the day can leave leaves wet all night, which is asking for trouble. Morning watering is much safer. If clumps are packed tightly and leaves overlap so much that they stay damp, thinning or dividing later in the season should go on your fall task list. In August, sanitation and airflow are your best tools.
7. Refresh mulch to hold moisture and cool the roots
There is hardly a garden lesson more useful in a Midwestern August than this: bare soil bakes. A 2- to 3-inch layer of mulch helps keep root zones cooler, slows evaporation, and reduces weed competition. Around my cannas, I like shredded bark, leaf mold, clean straw, or composted wood chips. I keep the mulch pulled back about 1 to 2 inches from the stalks so the crowns do not stay overly wet.
If your mulch has broken down to less than 1 inch, add enough to restore that cushion. In a bed 10 feet long and 3 feet wide, even two standard 2-cubic-foot bags can make a meaningful difference. The soil underneath stays more evenly moist, and the plants show less heat stress by late afternoon. On the hottest days, that can be the difference between leaves standing proud and leaves looking tired as dish rags on a clothesline.
8. Stake tall varieties before storms flatten them
Some cannas stay compact at 2 to 3 feet, but many of the older, grand varieties reach 5, 6, even 7 feet with bloom stalks rising above the leaves. In August, those tall stems catch wind like sails. One hard thunderstorm with 40-mile-per-hour gusts can split or topple a beautiful clump overnight.
I like to stake before I think I need to. A 5- or 6-foot bamboo cane or green metal support tucked discreetly behind the stalk works well. Soft garden twine or plant ties should hold the stem loosely, with room for movement. For larger clumps, I sometimes place 3 stakes around the outside and run twine in a wide circle to corral the whole planting. It is not glamorous work, but it saves heartbreak when summer weather gets rowdy.
9. Divide your attention between in-ground and container cannas
Cannas in pots need different August care than those in the ground. Containers dry out much faster, especially dark-colored pots in full sun. A 14- to 18-inch pot can need water every day in 90-degree weather, and sometimes twice daily if the plant is rootbound and the wind is up. If water runs straight through and the soil has shrunk away from the edge of the pot, soak it thoroughly until the root ball is fully rehydrated.
Container cannas also use up nutrients faster. I feed them more regularly but more gently, usually with a half-strength liquid fertilizer. If roots are circling densely and blooms are slowing despite good care, the pot may simply be too crowded. You probably will not repot in August unless you must, but make a note to divide that rhizome mass after frost or next spring. In-ground cannas generally ride out summer stress better because their roots can forage wider and deeper.
10. Pull weeds before they steal water and nutrients
It sounds humble, but August weeding is one of the best bloom-boosting chores there is. Weeds compete directly for moisture, and in dry spells they can rob more water than people realize. Crabgrass, pigweed, lamb’s quarters, and volunteer vines can quickly crowd the bases of cannas, restricting airflow and making pest checks harder too.
I prefer to weed after rain or after watering, when roots slide out more easily. A sharp hoe works well for shallow weeds, but around canna rhizomes I usually hand-pull to avoid nicking the crowns. Ten minutes every few days is far easier than an hour of wrestling a jungle. As my grandmother used to say, “One week’s weeds are one month’s trouble,” and she was right about that in flowers as surely as in beans.
11. Cut away seed pods if you want more blooms, not seeds
Many gardeners stop at deadheading old flowers, but in August it also pays to look for forming seed pods. If pollinated blooms are allowed to mature seed, the plant diverts energy into reproduction instead of continued flowering. Those pods can be attractive in their own way, but if your goal is nonstop color until frost, remove them while they are still small and green.
I snip the pod-bearing section just above a healthy leaf or side shoot. On vigorous plants, this often encourages another flush of bloom stalks within a couple of weeks, depending on the variety and weather. If you do want to save seed for experimenting, leave a pod or two on one plant and keep the rest trimmed. That way you get your curiosity satisfied without sacrificing the whole show.
12. Plan now for digging and overwintering, especially in cold-winter regions
August care is not only about the present display; it is also about setting up healthy rhizomes for next year. In much of the Midwest, cannas cannot stay in the ground over winter unless you garden in a reliably mild zone. Strong growth in August and September helps build plump rhizomes that store better after digging.
I start planning before frost sneaks up on me. I make sure I have labels, crates or cardboard boxes, and enough peat moss, sawdust, or dry wood shavings for storage. After the first light frost blackens the foliage, I cut stems down to about 4 to 6 inches, dig the clumps carefully with a garden fork 8 to 10 inches out from the base, and let them dry in a sheltered spot for a day or two. Stored at about 40 to 50 degrees in a dry basement or cellar, they usually winter well. Thinking ahead in August means less scrambling when October gets busy.