Frequently Asked Questions

Question:
How often should I water my roses?
Answer:

Modern roses, such as hybrid teas, floribundas, and grandifloras, require watering during hot, dry weather.  The frequency depends upon weather conditions and soil type.  In most gardens, a thorough watering every 7 to 10 days during...

Question:
What are some good raspberry varieties for Iowa?
Answer:

Suggested raspberry varieties for Iowa include:

Summer-Bearing Red Raspberries for Iowa

  • ‘Boyne’
  • ‘Latham’
  • ‘Killarney’

Fall-Bearing Red Raspberries for Iowa

...
Question:
The leaves on several of my hostas have turned yellow, then brown, and finally collapsed onto the ground. What is happening to my hostas?
Answer:

The hostas may have petiole rot.  Petiole rot is a serious disease of hosta.  It is caused by the fungus Sclerotium rolfsii var. delphinii.  (Petiole rot can also affect daylily, peony, phlox, columbine, and other...

Question:
When should I harvest cauliflower?
Answer:

Cauliflower should be harvested when the heads are smooth, firm, and compact.  Full-sized heads may be 6 to 8 inches across.  Overmature heads will begin to open up and become “ricey.”  Cauliflower may be placed in perforated...

Question:
A yellow, foam-like growth has suddenly appeared in my mulched perennial bed. What is it and will it harm my plants?
Answer:

The growth in your perennial bed is probably a slime mold. Slime molds are types of fungi. Slime molds feed on bacteria and other organisms in the mulch. They do not harm plants.

Slime molds are usually a temporary nuisance. Within a few...

Question:
When is the best time to plant rutabagas in Iowa?
Answer:

The rutabaga performs best when planted in summer for a fall crop.  Sow seed at a depth of 1/4 to ½ inch from June 15 to July 15 in Iowa.  Rows should be spaced 18 to 24 inches apart.  Thin the planting within a few weeks of...

Question:
When would be the best time to prune potentillas?
Answer:

Summer-flowering shrubs, such as potentilla and Japanese spirea, bloom in summer on the current year’s growth.  Prune summer-flowering shrubs in late winter or early spring (March or early April in Iowa).

Question:
How do you propagate forsythias?
Answer:

The forsythia is easily propagated from softwood cuttings. Softwood cuttings should be made from the current season’s growth in late June or early July. Using a sharp knife, cut off 4 to 6 inch long shoots. Pinch off the leaves on the lower half...

Question:
Several leaves on my tomato plant have curled up. Why?
Answer:

The curling of the tomato leaves may be a physiological disorder referred to as leaf roll.  Affected leaves roll upward and inward.  The leaves may also become thickened, giving the foliage a leathery appearance. 

Leaf roll...

Question:
How do I get rid of moles in my yard?
Answer:

Trapping is the best way to get rid of moles.  Trapping isn't easy, but it does work.  Patience and persistence are required.  Traps can usually be found in hardware stores and garden centers.  When using traps, carefully...

Question:
Do I need to remove my grass clippings to prevent thatch development?
Answer:

Grass clippings contribute very little to thatch development because clippings are primarily cellulose and decompose quickly.  There is no need to remove grass clippings when lawns are mowed properly.  Infrequent mowing of tall grass...

Question:
Is it safe to plant currants and gooseberries in home gardens in Iowa?
Answer:

Early in the 1900's, white pine blister rust (Cronartium ribicola) became a serious disease problem in the United States.  White pine blister rust requires both a currant or gooseberry (Ribes species) and white pine to...

Question:
How can I control blackspot on my roses?
Answer:

Blackspot is a common fungal disease of roses.  Symptoms of blackspot are circular black spots on the leaves.  Infected leaves turn yellow and drop prematurely.  Initially, symptoms develop on the lower leaves and gradually move...

Question:
Are black raspberries hardy in northern Iowa?
Answer:

Red and purple raspberries are hardy throughout the state.  Black raspberries, however, often suffer severe winter damage in northern Iowa and can be reliably grown only in central and southern portions of the state.  ‘Black Hawk’ (an...

Question:
My bearded irises are no longer blooming well. Why?
Answer:

The bearded irises may need to be divided.  Bearded irises should be divided every 3 to 5 years as the plants quickly become overcrowded and don’t bloom well.  July or August is the best time to dig, divide, and transplant bearded...

Question:
When should I harvest broccoli?
Answer:

Broccoli should be harvested when the head is fully developed, but before the flower buds begin to turn yellow and open.  At harvest, the terminal head should be tight, blue-green, and approximately 6 to 7 inches in diameter.  Most...

Question:
When should I cut gladiolus flowers for indoor use?
Answer:

Gladiolus for decorative indoor use should be cut as soon as the bottom flower on the spike has opened.  Most of the remaining blooms will open when the spike is brought indoors and placed in water.  When cutting gladiolus flowers,...

Question:
When should I harvest my summer squash?
Answer:

Harvest zucchini and other long-fruited summer squash varieties when the fruit are 1½ to 2 inches in diameter and 6 to 8 inches long.  Scalloped types are best when 3 to 5 inches in diameter.  Fruit should have soft skins (rinds) that...

Question:
Should I treat my ash trees to protect them from emerald ash borers?
Answer:

Insecticide treatments are available to protect ash trees from the emerald ash borer.   However, treatments should be undertaken only when necessary to prevent excessive and needless use of insecticides. 

Insecticide treatments...

Question:
When should I harvest okra?
Answer:

Harvest pods when 2 to 4 inches long.  (This is usually 5 to 6 days after flowering.)  Use a sharp knife or hand shears.  Handle the pods carefully as they bruise easily.  Since the pods develop rapidly, it’s often necessary...

Question:
Is there anything that can be done to make my Japanese wisteria bloom?
Answer:

The Japanese wisteria (Wisteria floribunda) is the most widely grown wisteria in the United States.  Unfortunately, it doesn't perform well in Iowa.  Most Japanese wisteria varieties (cultivars) do not bloom when grown in the...

Question:
What is the correct mowing height for a lawn in summer?
Answer:

Kentucky bluegrass and other cool-season grasses thrive in the cool weather of spring and fall.  Hot, dry conditions in summer are stressful for cool-season grasses.  Kentucky bluegrass lawns should be mowed at a height of 3 to 3½...

Question:
What are jostaberries?
Answer:

Jostaberries are a cross between black currants and gooseberries.  Plants are vigorous and may grow to a height of 6 to 8 feet.  Jostaberry fruit are similar in size to gooseberries and black in color.  Plants possess excellent...

Question:
Japanese beetles are devouring my roses. What can I do?
Answer:

Japanese beetles eat the foliage, fruits, and flowers of over 300 plants.  When feeding on foliage, the beetles consume the tissue between the veins, leaving a lace-like skeleton.  Flowers and fruits are sometimes devoured completely....

Question:
I have some small, purplish spots on the canes of my black raspberries. What is it and how can it be controlled?
Answer:

The small, purplish spots are most likely due to anthracnose.  Anthracnose is a serious fungal disease of raspberries, especially black raspberries.  The disease is readily recognized by the small, purplish spots that develop on young...

Pages