Thursday, August 14, 2008
Trimming an iris, prepping a poinsettia
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: I have a plot of Siberian irises that I am curious about. Two years ago, I cut back the seed pods and all greenery around mid-summer, when they started to look raggedy. The next spring they had very few blooms. Last year, I let them die back naturally and I think I had much better blooms. This year I have already cut down all the seed pods, but have left the leaves. They are now all bent over and looking very messy. Is it OK to cut the leaves or not?
A: Even though the iris leaves are bent over, if they’re still attached to their stout rhizome, which is the thick surface-growing horizontal stem from which roots emerge, their green parts are still making food through photosynthesis and pushing nourishment down for storage and use in the next year’s blooming. Removing iris seed pods is an optional cosmetic job, but its affect on the next year’s flowering is very small.
This tells us to cut and remove only all the brown leaf parts and leave most of the green leaf parts there to do nature’s work. Remove all other brown plant debris to make the iris planting bed look better.
Cutting back the seed pods and greenery two years ago caused much reduced blooming the following spring.
Q: What is the procedure for making a poinsettia bloom for the holidays? We were given a beautiful red and yellow flecks poinsettia last December that I would love to have in color this year. I put the poinsettia outside in its original pot in shade when our weather was warm enough in mid-spring. It’s still there now. It has made a lot of new growth this summer that I’ve kept trimmed so it wouldn’t be a tree by the fall. I guess the poinsettia has liked my monthly fertilizing with a blooming house plant food. What do I do now?
A: If you haven’t repotted your poinsettia this year, do so now while the plant is still outside. Gently knock off as much existing soil from the poinsettia root ball because fresh potting soil will help new root growth, which will enhance plant vigor in the fall and winter. Use a new pot that is only 1 inch larger than the present pot diameter to help prevent root rot.
Stop cutting the poinsettia back now because this holiday’s flowers will form on the tips of mature new shoots. Your poinsettia might not be as compact or moderate in size as last year, but that’s OK.
Bring it back inside to a bright, sunny spot before the nighttime temperatures drop below 55 degrees. Adjust your watering frequency as needed as potting soil can dry out differently inside your house.
Be sure that the poinsettia’s location indoors doesn’t receive any hot or cold drafts nor any hot or cold temperature changes. Any of these conditions can cause dropping of poinsettia foliage, which can result in an unattractive plant -- plus poor flowering.
Continue to fertilize the plant once per month with a soluble complete indoor plant fertilizer for blooming plants through the fall. The fertilizer product you’ve been using might be fine, but look to be sure that the “content analysis,” which is the descriptive list of three numbers identifying the nutrient percentages shows the middle number to be at least twice as big as the first number. That middle number is the percent of phosphorus, the nutrient that contributes greatly to flower and root growth.
On Oct. 1., create a controlled environment that mimics the shortness of days that poinsettias live through in their native hot areas and causes flowering to occur by moving the poinsettia to a heated, unused closet or by covering the plant with a light-proof box each evening. Provide the eight hours of sun by removing the box or taking the plant out of the closet around 8 a.m. daily.
Consistently create the long-night with short bright day environment until color shows, usually in early December.
If any insect or mite pest appears on your poinsettia, carefully wash off the pests with a mild soapy water solution followed by rinsing. You might find a commercially made pest spray that'll do the trick for poinsettias indoors.
