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Brown foliage on your maple trees & American elm?

Look may be seeds! 

Mary H. Meyer, Extension Horticulturist and Professor, Horticultural Science

Maple on left with masting, after distress. 
Abundant seed or fruit set in long-lived trees is called a mast year or masting. This year seems to be a mast year for maple and elm in Minnesota. 

Environmental cues or ideal pollination conditions could cause this huge seed production. Moisture and temperature are sensed by trees and their internal switches enable massive flowering followed by seed production. 
Excessive seeds at top of a maple tree.

Signs of masting

Homeowners can see the debris from flowers on driveways and sidewalks. Floral parts fall first, followed by seed a few weeks later. The helicopter wings of maples are familiar but the tiny, round beige elm seeds may not be as noticeable. 

How often does it happen? 

Research indicates maples have mast years every 2-5 years; sugar maple mast years reduce sap production the following year. 

Huge seed production may follow stressful growing conditions; also known as a distress crop
when a plant will put all resources (even if it may mean death to the plant), into seeds just to get their genes into the next generation.

Is it a normal mast year or distress for your landscape tree?

Stem girdling roots.
Trees with stem girdling roots may have abundant seeds in their final years. (See image right.) Stem girdling roots will kill a tree and should be corrected when the plants are grown in the nursery.

Signs of stress (or distress)

Examine your trees and avoid any environmental stress such as changes in soil grade, compaction, trunk damage, root disturbance, etc.  Keep plants well watered during times of drought to minimize any environmental stress. 

Here are two things you can do about the seed boom this year: 
  1. Have fun with the abundance of helicopter seeds, a childhood memory that all of us can enjoy
  2. Start an annual journal of seed set for your trees to track your trees' mast years.

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