Extension News

Ask the ISU Extension Garden Experts: Seed Germination and Fall Raspberries

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 e-mail us at hortline@iastate.edu. For more gardening information, visit us at Yard and Garden Online, http://www.yardandgarden.extension.iastate.edu.

2/20/2009

Some of the seedlings that I start indoors collapse and die shortly after germination.  Why? 

Damping-off is probably responsible for the collapse and death of your seedlings. Damping-off is caused by several different fungi. Environmental conditions usually associated with damping-off are poorly drained potting soil and overwatering.  Damping-off can be prevented by using clean containers, a sterile, well-drained potting mix and by following good cultural practices.  Previously used containers should be washed in soapy water, then disinfected by dipping in a solution containing one part chlorine bleach and nine parts water. Flower and vegetable seeds need an evenly moist potting mix for good germination.  After germination, allow the potting soil to dry somewhat between waterings. 

When should I start flower and vegetable seeds indoors? 

The crop time (number of weeks from sowing to planting outdoors) for several popular flowers and vegetables are as follows: 10 to 12 weeks - geranium; eight to 10 weeks - petunia and impatiens; six to eight weeks - marigold, pepper, and eggplant; five to seven weeks - tomato, cabbage, broccoli and cauliflower; three to four weeks - cucumber, watermelon, muskmelon and squash.  Always check the seed packet if unsure of the correct sowing date. 

What is the proper way to prune fall-bearing yellow raspberries in spring? 

Fall-bearing yellow raspberries naturally produce two crops.  The first crop is produced in late summer or early fall at the tips of the current season’s growth. The following year, the lower portions of the same canes produce a summer crop. After the second crop, the canes die.  Each spring, new shoots emerge from buds located at the base of the previous season’s growth and on the plant’s roots. 

Fall-bearing yellow raspberries can be pruned two different ways in spring. 

Option 1 is to remove all weak, diseased and damaged canes at ground level in March or early April.  Leave the most vigorous canes, those approximately 1/4 inch in diameter when measured 30 inches above the ground.  After thinning, remaining canes should be spaced about six inches apart.  Also, prune out the tips of the canes that have died due to winter injury.  Cut back to live tissue.  If the canes sustained little winter dieback, remove the top 1/4 of the canes. Cane-tip removal or “heading-back” prevents the canes from becoming top heavy and bending over under the weight of the crop.  This pruning method allows the plants to produce two crops per year. 

Option 2 is to prune all canes back to ground level in March or early April.  While the plants won’t produce a summer crop, the late summer/early fall should mature one to two weeks earlier.  Also, total crop yield is typically larger using the one-crop system versus two-crop system. 

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Contacts :
Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu 

Del Marks, Extension Communications and External Relations, (515) 294-9807, delmarks@iastate.edu