Frequently Asked Questions

Question:
There is a large, hard growth on the cane of one of my roses. What is it?
Answer:

The large, hard growth is probably crown gall.  Crown gall is caused by the bacterium Agrobacterium tumefaciens.  The bacterial disease can infect roses, grapes, apples, raspberries, willows, euonymus, and many other woody...

Question:
The bottom of my black raspberry leaves are covered with an orange substance. What is it?
Answer:

The orange substance on your black raspberry leaves is orange rust.  Orange rust occurs on black and purple raspberries and most varieties of blackberries.  Orange rust does not occur on red raspberries. 

Orange rust...

Question:
How can I control the iris borer?
Answer:

The iris borer is a serious pest of bearded irises.  The mature stage of the iris borer is a grayish moth.  Female moths lay eggs on iris foliage and other nearby plants in late summer/early fall.  The eggs hatch the following...

Question:
When should I plant Chinese cabbage?
Answer:

Chinese cabbage performs best when planted in summer for a fall crop.  (Chinese cabbage frequently goes to seed when planted in spring.)  Sow the seed of Chinese cabbage at a depth of 1/4 to ½ inch in July.  Rows should be spaced 2...

Question:
Can I plant my Easter lily outdoors after it is done blooming?
Answer:

Individuals wishing to save their Easter lily (Lilium longiflorum) should place the plant in a sunny window after flowering.  Continue to water the plant when needed.  Fertilize once every 2 weeks with a dilute fertilizer...

Question:
Can sweet corn be planted near popcorn in the garden?
Answer:

Sweet corn should be isolated from popcorn and field corn to prevent cross-pollination.  The quality of the sweet corn will be lowered if it’s cross-pollinated by other types of corn.  For example, sweet corn pollinated by popcorn will...

Question:
There are big, hairy worms and tent-like structures in my walnut tree. What are they and how do I get rid of them?
Answer:

The “worms” are likely fall webworms.  Fall webworms are hairy, tan to yellow caterpillars.  As they feed, fall webworms construct tents or webs at the ends of branches.  Tents are initially small, but the caterpillars enlarge the...

Question:
When should I harvest herbs?
Answer:

Most herbs are ready to be harvested when flower buds appear on the plants, but before the buds open.  The leaves contain the maximum amount of volatile oils at this stage of growth, giving the greatest flavor and fragrance to the finished...

Question:
My bittersweet vine doesn't produce any fruit. Why?
Answer:

American bittersweet (Celastrus scandens) is dioecious.  Dioecious plants bear male and female flowers on separate plants.  Gardeners need to plant at least one male and one female bittersweet vine to produce fruit. ...

Question:
When mowing the lawn, what is the proper mowing height?
Answer:

Kentucky bluegrass lawns should be mowed at a height of 2½ to 3 inches in the spring and fall months.  Mow bluegrass lawns at a height of 3 to 3½ inches in June, July, and August.  A higher mowing height in summer helps to cool the...

Question:
When do I harvest currants?
Answer:

Currants typically ripen over a 2 to 3 week period.  Fully ripe currants possess the characteristic color of the variety (red, white, or black), are slightly soft and juicy.  For jellies and jams, harvest currants before the berries are...

Question:
How do I care for garden geraniums?
Answer:

Garden geraniums (Pelargonium x hortorum) are attractive flowering plants for beds, borders, containers, hanging baskets, and window boxes.  Geraniums are easy to grow and provide color in the garden from May to frost....

Question:
My purple raspberry canes grow several feet tall and eventually flop over onto the ground. What can be done to prevent this?
Answer:

The shoot tips of purple and black raspberries should be pinched or cut off when the new growth reaches a height of 36 to 48 inches.  Remove the top 3 to 4 inches of the shoots.  Pinching encourages lateral shoot development and...

Question:
Are Louisiana irises hardy in Iowa?
Answer:

Louisiana iris is the collective name for several species of iris which are native to Louisiana and boggy coastal areas from Florida to Texas.  They are prized for their colorful white, blue, red, or yellow flowers.  Louisiana irises...

Question:
My cucumber plants are blooming heavily, but aren't producing many fruit. Why?
Answer:

Cucumbers and other vine crops are monoecious.  Monoecious plants have separate male and female flowers on the same plant.  Male and female flowers are similar in appearance.  However, the female flowers have small, immature fruits...

Question:
How do I care for a grapefruit tree?
Answer:

Grapefruit and several other types of citrus can be grown indoors in Iowa.  Indoors, place citrus plants in a sunny south or west window.  Water plants regularly when growing in spring and summer, less often in winter.  In spring...

Question:
The ears on my sweet corn are poorly filled. What are possible causes?
Answer:

Poorly filled ears are usually the result of poor pollination.  Hot, dry winds and dry soil conditions may adversely affect pollination and fertilization and result in poorly filled ears. Water sweet corn during pollination if the soil is...

Question:
My magnolia is infested with magnolia scale. What are my control options?
Answer:

Magnolia scale is the largest scale insect in Iowa.  Sap feeding by the scales causes stress to heavily infested plants and can result in stunted growth, yellowish foliage, branch dieback, or death of the plant.  Magnolia scales produce...

Question:
Can I place weeds and diseased plant debris from the vegetable garden in the compost pile?
Answer:

It would be best to place weeds that are producing seeds and diseased plant debris in biodegradable bags and have the material picked up and composed by a municipal or commercial composting facility.  The temperatures in home compost piles...

Question:
There are brown streaks in my apples. What is the cause and how can it be prevented?
Answer:

The brown streaks in the apples are probably due to the apple maggot.  The apple maggot is the most serious insect pest of apples in Iowa.  Apple maggot damage appears as knobby, misshapen fruit with small pits or blemishes on the fruit...

Question:
Some of the leaves in my river birch are turning yellow and dropping to the ground. Why?
Answer:

Hot, dry weather may be responsible for the leaf drop on the river birch. River birches shed some of their leaves in hot, dry weather.  Leaves in the interior of the river birch turn yellow and drop to the ground.  Healthy, well-...

Question:
How often should I mow my lawn?
Answer:

Kentucky bluegrass lawns should be mowed at the height of 2½ to 3 inches in spring and fall.  Set the mower blade to a height of 3 to 3½ inches during summer. 

As a general rule, never remove more than 1/3 of the total leaf...

Question:
I have several rows of grapevines. What would be a good cover crop between rows?
Answer:

Kentucky bluegrass is an excellent choice.  Bluegrass provides good cover, yet is less competitive than other cover crops.  Late summer (mid-August to mid-September) is the best time to establish bluegrass by seed.  Do not sow...

Question:
There are blister-like growths on the undersides of ivy geranium leaves. What is the problem?
Answer:

Oedema is probably responsible for the lesions on the undersides of the ivy geranium leaves.  Oedema is not caused by an insect or disease pathogen.  It is a physiological problem.  Oedema is most often encountered in greenhouses...

Question:
Can blackberries be successfully grown in Iowa?
Answer:

The growth and fruiting characteristics of blackberries are similar to raspberries.  The blackberry plant’s roots and crown are perennial, while its stems or canes are biennial.  Blackberry canes are strictly vegetative during the first...

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