Frequently Asked Questions

Question:
There are erect, hair-like growths on the upper leaf surface of my maple tree. Should I be concerned?
Answer:

The hair-like growths are likely galls.  Galls are abnormal growths of plant tissue induced to form by mites, insects, or other small organisms.  The hair-like gall on the maple leaves is probably the maple spindle gall. 

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Question:
My crabapple has begun to drop some of its leaves. Why?
Answer:

The leaf drop is probably due to apple scab. Apple scab is a fungal disease caused by the fungus Venturia inaequalis. Cool, wet weather in spring favors apple scab development. Crabapple varieties differ in their susceptibility to apple...

Question:
There is a large growth on the trunk of my maple tree. What is it?
Answer:

The growth on the trunk of the maple tree is likely a burl.  Burls are abnormal swellings or growths that develop on the trunks and branches of trees.  Burls can be found on deciduous trees and evergreens.  The exact cause is...

Question:
There are golf ball-sized growths with horn-like projections on the branches of my pin oak. What are they?
Answer:

The growths on the pin oak are a type of gall.  Galls are abnormal growths of plant tissue induced to form by mites, insects, or other small organisms.  The galls on the pin oak are called horned oak galls because of the horn-like...

Question:
Which evergreen trees perform well in home landscapes in Iowa?
Answer:

Only a small number of evergreen trees perform well in Iowa.  Some evergreens, such as Scotch pine and Austrian pine, have serious disease problems and are no longer recommended for planting in Iowa.  The most reliable evergreens for...

Question:
Why are some of my cucumbers misshapen?
Answer:

Poorly-shaped fruit are usually the result of poor pollination.  Poor pollination may be due to cool, wet weather and improperly applied insecticides that limit bee activity.  When insecticides are necessary, select an insecticide with...

Question:
Why are some of my cucumbers bitter?
Answer:

The bitterness in cucumbers is produced by the compound cucurbitacin.  Cucurbitacins are normally found in the leaves, stems, and roots of cucumber plants.  The cucurbitacins spread from the vegetative parts of the plant into the...

Question:
Which perennials grow well in dry soils?
Answer:

Perennials that tolerate dry soils include yarrow (Achillea spp.), wormwood (Artemisia spp.), butterfly weed (Asclepias tuberosa), false blue indigo (Baptisia australis), threadleaf coreopsis (Coreopsis...

Question:
My tomato plants are flowering, but aren’t setting fruit. Why?
Answer:

Unfavorable weather conditions are the primary reason for blossom drop on tomatoes.  High daytime temperatures (above 85 degrees Fahrenheit) and low nighttime temperatures (below 55 degrees Fahrenheit) interfere with pollination, causing...

Question:
There are wart-like growths on the undersides of the leaves on my hackberry. What are they?
Answer:

The wart-like growths on the hackberry leaves are galls.  Galls are abnormal growths of plant tissue induced to form by mites, insects, or other small organisms.  They are quite common on trees.  

The gall found on the...

Question:
There are white, fuzzy objects on the branches of my maple tree. Are they harming the tree?
Answer:

The white, fuzzy objects on the branches of your maple tree are wooly alder aphids.  (The insect is also known as the maple blight aphid.)  Wooly alder aphids feed on the sap of maple trees from bud-break until late June.  Then...

Question:

Which azaleas can be successfully grown in Iowa?
Answer:

Azaleas in the Northern Lights Series possess excellent cold hardiness and perform well in Iowa. (The Northern Lights Series is a group of hybrid azaleas developed and released by the University of Minnesota.  All cultivars in the series...

Question:
Which rhododendrons can be successfully grown in Iowa?
Answer:

The most widely grown rhododendrons in Iowa are the Weston hybrids.  Introduced by the Weston Nursery in Massachusetts, these cultivars possess excellent cold hardiness.  Weston hybrids include ‘PJM’ (lavender pink flowers), ‘PJM...

Question:
Can azaleas and rhododendrons be successfully grown in Iowa?
Answer:

There are more than 900 species and innumerable cultivars of azaleas and rhododendrons.  However, only a small number perform well in Iowa.  To be successful, the Iowa gardener must select cold hardy cultivars, choose suitable planting...

Question:
What are suitable planting sites for azaleas and rhododendrons?
Answer:

Proper site selection is important when planting azaleas and rhododendrons.  Azaleas prefer partial to full sun.  Rhododendrons perform best in protected sites in partial shade.  Areas that receive morning sun and afternoon shade...

Question:
Should everbearing and day-neutral strawberries be renovated like June-bearing strawberries?
Answer:

Everbearing and day-neutral strawberries should not be renovated like June-bearers.  Everbearing and day-neutral strawberries are most productive when the plants are maintained as large, single plants.  All runners that develop on...

Question:
How do I control grasses in my iris bed?
Answer:

Annual grasses, such as crabgrass and foxtail, can be controlled by hand pulling.  

Perennial grasses, such as quackgrass, are much more difficult to control as they spread via underground stems or rhizomes.  (All of the rhizomes...

Question:
Why are my rhubarb stalks small and spindly?
Answer:

Newly planted rhubarb will initially produce small, spindly stalks during its 2 year establishment period.  The stalks of large, old plants may be small and spindly because of overcrowding.  Poor plant vigor due to poor cultural...

Question:
When should I divide my perennials?
Answer:

The best time to divide perennials varies with the different plant species.  Early spring (just as new growth begins to appear) is the best time to divide aster, chrysanthemum, hosta, bee balm, sedum, yarrow, obedient plant, and ornamental...

Question:
Is it necessary to fertilize annuals growing in containers?
Answer:

Plants in containers need to be fertilized on a regular basis as nutrient levels in potting mixes quickly fall due to absorption by plants and leaching during watering.  

Many commercial potting mixes contain a slow release fertilizer...

Question:
Is it necessary to deadhead daffodils?
Answer:

Deadheading is the removal of spent flowers.  While tulips should be deadheaded immediately after flowering, it is not necessary to deadhead daffodils.  The vigor of tulip bulbs quickly declines if tulips are not promptly deadheaded and...

Question:
What would be a good planting site for chrysanthemums?
Answer:

Chrysanthemums perform best in moist, well-drained soils.  Avoid wet, poorly drained sites.  Improve hard, difficult-to-work soils by incorporating 2 to 3 inches of organic matter, such as compost, peat, or barnyard manure, into the...

Question:
How soon will a newly planted fruit tree begin to bear fruit?
Answer:

Fruit trees purchased from nurseries and garden centers are usually 1- to 2-year-old plants.  The length of time from planting to fruit bearing varies with the species of fruit, the cultivar, and whether the tree is dwarf or standard....

Question:
What are some good annuals for shady garden areas?
Answer:

Annuals that can be successfully grown in shady areas include wax begonia (Begoniasemperflorens-cultorum), impatiens (Impatiens walleriana), lobelia (Lobelia erinus), coleus (Solenostemon...

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