Ask the Master Gardener: Little bumps on maples won't affect tree health

Little red bumps on maple trees, called Maple Gall Bladder, are abnormal plant growths caused by insects, mites, fungi, bacteria or viruses. Photo by Jennifer Knutson

Dear Master Gardener: My three-year-old crimson maple has little red bumps all over it. What is it? Should I spray my tree with something?

Answer: Your maple tree has Maple Bladder Gall. Galls are abnormal plant growths caused by insects, mites, fungi, bacteria or viruses. They can be caused by feeding or egg-laying of insects and mites. Galls are typically formed during the late spring growth period and become noticeable only after they are fully formed. Most galls do not affect plant health, so control is rarely recommended. Because the timing of chemical spray is absolutely critical, chemical applications are usually not effective. Once galls are formed, it is too late for treatment.

Dear Master Gardener: A friend has beautiful, huge hostas in his garden. How long does it take for a hosta to reach mature size and what large hostas do you recommend?

Answer: Hostas are categorized in two ways: leaf blade size and clump size. The American Hosta Society size classification for hostas focuses on leaf for show purposes, not the mature size of the clump. The leaf section of giant-leaved hostas measures 120 or more square inches. Area is defined as leaf blade length multiplied by leaf blade width. There are no official categories for hosta clump size, but the five most often used are dwarf, small, medium, large and giant. Mature mound height is used for defining hosta sizes. From a practical gardening and landscape design perspective, this is a much better criterion for defining a hosta’s size than leaf blade area. The mature foliage mound height of a dwarf is less than eight inches, a small is 9-14 inches, a medium is 15-22 inches, a large is 23-29 inches, and a giant is over 30 inches. In good conditions, giant hostas will reach their mature size in five to eight years. Your key to success for growing giant hostas is proper soil preparation, plentiful moisture and appropriate light exposure. The single most important factor in ensuring the success of any plant is thorough soil preparation because no amount of watering and fertilizing will make up for poor soil preparation. Plant hostas in rich, well-draining soil with added organic matter, such as compost. For large hostas, the hole should be at least three feet in diameter and perhaps as much as five feet, depending on the width of the mature hosta. Hostas do not have deep roots, so the hole does not need to be more than 18 inches deep. Giant hostas in particular need a lot of moisture. Without enough water during the growing season, they will stop growing. As a general rule, blue and dark green hostas should be in shade; whereas those with yellow in them need more sunlight to bring out their color.


Following are some popular giant hostas:

  • Blue Angel has a mature size of 71 inches wide by 36 inches high. It becomes a graceful, cascading mound of thick, dark blue-gray leaves. It prefers a few hours of morning sun followed by light shade. It tolerates dry soil when established.

  • Earth Angel matures to 61 inches wide by 36 ½ inches high and is one of the most outstanding cream-margined, blue-leaved hostas. It has moderate growth rate and does best in morning sun, followed by light shade.

  • Empress Wu is one of the largest hostas on the market and can reach 70 inches wide by 48 inches high at maturity. If grown in fertile soil with moisture retention, it can get even larger. It is dark green with gigantic, wavy, corrugated leaves. Empress Wu performs best in part to full shade.

  • Frances Williams becomes a dense mound with a mature clump size of 51 inches wide by 32 inches high. It has blue-green leaves that are widely margined yellow turning creamy beige with some chartreuse streaking. If grown in low light conditions the margins will remain chartreuse and the base color a darker blue. Site in light to moderate shade to prevent the edges from scorching. It can be slow to establish.

  • Gentle Giant matures to 68 inches wide by 45 ½ inches high. It has bluish leaves and forms a huge, upright mound. Its leaves are thick and leathery, intensely glaucous blue-green with prominent veins. Strong sunlight will melt the wax off the leaves of all blue hostas, so sit them in shade to hold their blue color. It has a rapid growth rate.

  • Northern Exposure matures to 70 inches wide by 36 inches high. It can be slow to establish, but is worth the wait. It has thick, seer-suckered, blue-green leaves with cream-colored margins. It needs full shade or filtered shade.

  • Sagae is large to giant reaching a mature clump size of 71 inches wide by 30 inches high. It makes an impressive mound. Its leaves are thick, blue-gray with creamy irregular margins. It requires light to moderate shade. It is slow to show its potential but eventually forms a huge specimen.

  • Sum and Substance matures to 60 inches wide by 36 inches high, often exceeding its registered dimensions. It has thick, light green leaves that turn chartreuse to muted gold depending on light levels. It does best in morning sun.

  • T-Rex reaches a mature clump size of 80 inches wide by 30 inches high. It is slow to start but eventually becomes a huge, impressive foliage mound. It has immense, heavy green leaves that cascade downwards becoming creased and pleated. It needs light shade and lots of moisture.

Dear Master Gardener: Rose chafers have eaten all the blooms from my roses and peonies. Although I don’t like using insecticides, is there one I can use to get rid of them?

Answer: Rose chafers are found throughout Minnesota, especially in areas with sandy soils, such as ours. They feed on the foliage of many plants, but primarily feed on the blossoms of roses and peonies. If you have large numbers of rose chafers, you can treat plants with a garden pesticide. More applications may be necessary when they are numerous. Look for a pesticide that has bifenthrin, esfenvalerate, cyfluthrin, imidacloprid, permethrin or carbaryl as an active ingredient. The good news is -- rose chafers are usually done feeding around the end of June.

University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. All information given in this column is based on university research. To ask a question, call the Master Gardener Help Line at 218-454-GROW (4769) and leave a recorded message. A Master Gardener will return your call.


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