Extension News

Ask the ISU Extension Garden Experts: Bagworms, Hanging Planters and Moving Spring-flowering Bulbs


Note to media editors: Got gardening questions? Call the Hortline at 515-294-3108, Monday-Friday from 10 a.m. to noon and 1 to 4:30 p.m., or send an e-mail to hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, http://www.yardandgarden.extension.iastate.edu.


When should I spray for bagworms on my evergreens? 
Bagworms are caterpillars that live inside spindle-shaped bags. (The bags somewhat resemble small Christmas tree ornaments hanging from the tree.) Bagworms feed on the foliage of a wide variety of trees and shrubs. However, they are most commonly found on juniper, arborvitae, spruce and other evergreens. The spindle-shaped bags are made of silk and bits of foliage (needle) fragments. The bags protect the caterpillars from their natural enemies. Bagworms are most often found in the southern half of Iowa. 

Bagworms over-winter in the egg stage inside female bags attached to plants. In Iowa, egg hatch typically occurs in late May to mid-June. Insecticides, such as Bacillus thuringiensis, spinosad, Sevin, permethrin or bifenthrin, should be applied shortly after egg hatch. 

One way to determine the best time to treat is to frequently inspect trees and shrubs (beginning in late May) that were infested last year. This will take time and diligence as the newly emerged caterpillars and their bags are quite small. Also, newly constructed bags with fresh plant bits are effectively camouflaged amongst the needles and are hard to find. Mother Nature also provides some helpful clues. Bagworm egg hatch typically occurs when catalpas and Japanese tree lilacs are in bloom in the area.

How often should I water plants in hanging baskets? 
Plants in hanging baskets need to be watered frequently (especially in summer). Potting mixes are light, well-drained and dry out quickly. Plus, hanging baskets may contain several plants. In general, water plants in hanging baskets when the soil surface becomes dry to the touch. On hot, sunny days it may be necessary to water once a day. When watering hanging baskets, be sure to apply water until water begins to run out the bottom of the container. This ensures that the entire soil ball has been moistened.

Do not let the potting mix dry out completely. Plants will wilt if the potting mix dries out excessively. Plus, it’s more difficult to moisten the potting mix when it has dried out completely. If the potting mix gets too dry, it will separate (pull away) from the side of the container. If you attempt to water from above, most of the water will flow between the soil ball and container and run out the drainage holes in the bottom of the basket. Unfortunately, most of the potting mix will remain dry. When the potting mix gets excessively dry, place the basket in a tub of water for one or two hours. This forces water to be absorbed slowly from the bottom of the container. Do not keep the basket in the tub of water for more than two hours as this may result in root rot problems. 

I would like to move some of my spring-flowering bulbs. When can they be dug? 
If you would like to dig and move spring-flowering bulbs, such as tulips and daffodils, wait until the foliage has turned brown and died. Once dug, the bulbs can be separated and replanted immediately. If planting isn’t possible, dry the bulbs for one or two weeks and then store them until fall. Place the dried bulbs in mesh bags and store them in a cool (50 to 60 F), dry location until fall planting. Periodically check the bulbs during summer and discard any that show signs of decay. 


Contacts :

Richard Jauron, Horticulture, 515-294-1871, rjauron@iastate.edu

Willy Klein, Extension Communications and External Relations, 515-294-0662, wklein@iastate.edu

One high resolution photo of a bagworm-infested spruce tree is available for use with this article. bagworm on spruce