Canna lilies do best in full sun

Question: I have two large cannas, both red/orange in color. One is planted to the left of my entry gate, where it gets sun most of the day (call it plant No. 1), and the other to the other side of the gate, where it gets sun maybe 60 percent of the day (plant No. 2) In mid-afternoon it is in the shade. The garden faces south. They have both flowered twice with long colorful stalks, but since about seven weeks ago neither has grown any stalks for future flowers. Plant No. 1 is very burnt around all the leaf edges, while plant No. 2 looks very healthy. They are both watered on my drip system. They were both cut back to the ground last winter and started to regenerate in March. I have fed them now and then with Miracle-Grow, but not too much.

Answer:Let's cover a little bit of general canna lily care first. Cannas are tropical to subtropical plants originating in the tropics and subtropics of North America. They perform best in full sunlight provided they have adequate water. They can be grown as bog plants or plants surrounding pond areas. The biggest problems growing cannas here are probably trying to grow them in desert landscapes surrounded by rock mulch, not enough water, too much shade, not dividing them every three to four years, not pruning out the old flowers regularly, and not fertilizing them regularly and not using an organic mulch where they are planted.

Location is important. Plant in locations away from hot walls or reflected light but in full sun or very nearly so. In our climate they also do well under very light shade, but not at all in deep shade. A half day of sunlight is not enough.

They like organic soils so they do not perform well in desert landscapes where these plants are surrounded by rock mulch. Desert landscapes should have a high water use area devoted to plants that require more water than true desert plants. These are the areas normally devoted to plants that will shade the walls of the house or provide shade in outside living areas. These are also the areas where tropical looking plants like cannas will perform best in soils that have been modified with lots of organic matter and mulched with organic mulches.

Cannas are a clumping, herbaceous perennial that increase the size of its clump by making short underground shoots called rhizomes. You can expect a one gallon canna lily to be 18 inches across and double its height in three years if properly maintained.

Because these plants increase in size by forming clumps through rhizome production they should be lifted with a garden spade, or shovel if you are careful, in the late fall and the clumps divided every three or four years. If clumps are not divided, then the number and quality of the flowers will be reduced regardless of how much water and fertilizer they receive.

The clumps can be divided with a sharp knife, allowing the cut ends of the rhizomes to callus over by placing them outside in the shade for a few days after cutting. The rhizomes are replanted about 3 to 4 inches deep and 12 to 18 inches apart. The remainder can be shared with friends.

My guess is that your problem is a lack of soil organic matter, sunlight, watering, mulching and not getting rid of spent flowers. Regarding your plants I would dig them up this fall and divide them even if they are not that big yet. Let the cut ends heal over in the shade and open air for three to four days. This will give you the chance to modify the soil where they are planted with some rich organic matter. Mix the existing soil with the organic amendments in a 3-to-1 ratio. Plant them in full sun.

Fertilize with your favorite phosphorus fertilizer when you replant the cut rhizomes this fall. Make sure your drip emitters wet the soil surrounding all the clumps. Use emitters that will give enough water to thoroughly wet the soil. Mulch with an organic mulch on the surface about 2 inches deep. Fertilize monthly with your favorite all-purpose fertilizer for flowering plants. When the flowers are spent, cut the flower stalk almost all the way to the ground. You should see new breaks form below the cut and send up new flower stalks. Cutting is important.

Q: We have an African Sumac tree that keeps shooting up suckers from its base. Is it perhaps planted too deep or can you tell us what the problem and solution might be? Two of the same trees were planted at the same time and only one of them has this problem.

A: This can be a problem with African sumac all over the trunk when they are young and as it gets older this tendency climbs into the scaffold branches. The problem can be accentuated if you cut off these suckers (actually they are called watersprouts if they are above ground) with a pruning shears. The short stubs left behind will create more surface area for new suckers to arise.

I prefer to pull the suckers from the trunk in the early spring. Frequently in early spring there is a time when small sprouts are weakly attached to the tree. By pulling down on these sprouts at this time of year you can pop them from the tree along with a small piece of the trunk just under the bark.

This small piece of wood is important. This wood really hasn't made up its mind yet what it wants to be. If the sucker is cut, it will probably cause more suckers to pop up. If you can remove this confused part of the wood, you will reduce the chance for suckering at this point.

If the suckers are too large to pop from the trunk, then a little surgery with a sterile knife right around the base of the sucker should help reduce the suckering. No need to paint the cut areas.

Q: I have oleander on both sides of a concrete wall. At one end of both sides the oleander thrives beautifully but grows gradually weaker going to the opposite end of the wall. I also have two oleanders in other areas that look very healthy but no blossoms. I am totally confused as to how to treat this problem. I have a drip system.

A: When oleanders are not getting enough water, the plants will be thin, meaning easy to see through the canopy. When they are getting enough water they will be dense with no way to see through it. If there is plenty of water then growth should be fast and vigorous with large leaves.

My best hunch is that this is a water problem. My guess is that the weaker oleanders are the furthest downstream on your drip system. Another hunch is that you are not using what are called pressure compensated drip emitters. These are dripper emitters or drippers that keep the same pressure all the way down the drip system. Emitters that are not pressure compensated will emit more water at the emitters closest to the valve and get less and less as the drippers are located further and further from the valve.

A notorious drip emitter for causing this kind of problem is the variable or adjustable emitters that allow you to turn a knob and adjust the flow of water from the emitter to up to ten gallons per hour in some cases. These are no longer drip emitters but tiny bubblers. Oleanders are very drought tolerant but very high in water use if you want full and lush bushes. If these are the large oleanders and not the dwarf types then you would probably need at least three drip emitters per plant in sandy soils and I would probably water them once to twice a week in midsummer.

Oleanders that are underwatered also will not produce as many flowers. But the nearly universal reason they don't have flowers is because they get sheared a couple of times a year by gardeners wanting to keep them in check. Oleander flowers are produced on this year's wood and so shearing them during the growing season will remove all of the wood that would produce the flowers a few weeks later.

Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.


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