Q: The leaves of our maple tree have red bumps. I’m wondering if they’re going to damage the tree, of if there is something I can do in the spring to prevent it. — Alan R.
A: The bumps, which are often green before turning red, are called maple leaf galls. I receive a large number of questions every June, as the galls appear.
The galls are formed by tiny mites feeding on developing leaves, causing the leaves to produce abnormal cell growth, which encases the mite inside. The mite continues to feed and grow, nestled safely inside the protective gall.
In most cases, galls are not numerous enough to harm the tree, causing little or no effect. Galls usually look worse than they are. Nearly every research university recommends that control options aren’t needed, as most galls don’t cause any severe damage to plant health.
Chemical applications aren’t effective once the galls start to form, because the mite is safe inside. Many gall-forming mites spend the winter in the crevices of tree bark on the trunk and adjacent branches. To attempt early control, apply horticultural oil to the tree trunk and main branches just as buds are beginning to swell and open.
Besides maples, leaf galls are common on hackberry, oak, poplar, plum and others.
Q: I planted a Strawberry Sundae hydrangea, and I’m wondering what type of fertilizer I should use, and how often. For the rest of my shrubs, can I just use Miracle Gro fertilizer? I have an assortment of different shrubs. — Jan S.
A: Strawberry Sundae hydrangea belongs to the species Hydrangea paniculata, which is well-adapted to the region. Other species of hydrangea adapted to other parts of the country can be manipulated to change color, either pink or blue, depending on how you acidify the soil, but those types are too finicky for our growing conditions.
Paniculata hydrangeas, including your Strawberry Sundae, will retain their same original beautiful color regardless of how you manipulate the soil. Hydrangeas do grow and bloom better with proper nutrition, which can be supplied in several ways.
You could shop your garden center for fertilizers specially tweaked for flowering shrubs. You could also use an all-purpose granular 10-10-10 fertilizer which provides well-balanced nourishment for leaves, roots, and flowers. You can certainly use water-soluble types that list shrubs on the label, such as Miracle Gro and similar brands. These would be fine for your hydrangea and any other shrubs.
One advantage of using the water-soluble fertilizers is their quick availability to shrub roots. Granular fertilizers must first dissolve into a water solution so roots can absorb the nutrients. Always follow the label directions when using any fertilizer.
Q: I’ve noticed holes on my hosta leaves every year, and have learned that it’s from slugs. What’s the best way to control and prevent them, so it’s not a problem this year? — Russ L.
A: Slugs are black or brown mollusks, like a snail without its shell. They feed mostly at night, creating holes in hosta and other wide-leaved plants. During the day they crawl into moist places, often hiding under materials like boards. Slugs are more active in shaded areas of the yard, where damp areas are prevalent.
Because slugs aren’t insects, insecticide sprays and powders have no effect. Garden centers carry slug baits that can be effective if used according to label instructions. An old-time method is to sink beer-filled trays at soil level, into which slugs will crawl and drown.
Plants that are slug-prone can be made less attractive by circling the ground around the plants with scratchy material such as sand, diatomaceous earth, or even finely crushed eggshells.
If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at firstname.lastname@example.org. Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.