When to apply which Fertilizer

bloomingtoninbloomMarch 14, 2007

Last spring I moved to a new house in Indiana and created a large raised bed. In the middle of the lawn there was a huge mass of iris rhizomes that the neighbors told me hadn't bloomed in years. I transplanted about 40 of them to the new bed and last August planted a number of dark variety irises I bought from Schreiner's (Before the Storm, Anvil of Darkness, Midnight Oil, etc.

I've read that I should apply a superphosphate or 6-10-10 about six weeks before bloom, but new to growing irises, I don't know when to expect blooms in this zone (5B-6A). Any advice on approximately when I should apply a fertilizer? Also, any thoughts on which fertilizer would be best would be greatly appreciated.

Thanks! :)

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I will be eagerly awaiting the forum's response. While I know that our irises should be fertilized 6 weeks prior to bloom. But, a search of the fertilizer shelves at our gardening stores does not turn up a ready mixed fertilizer with low nitrogen. Please tell me what most of you use. Brand? Where do you find it? Etc. Thanks in advance.

Bloomington, we found that weather conditions really affect bloom schedule. In the last two years, there was a two week variance!

    Bookmark   March 15, 2007 at 10:27AM
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marvine(z7/8 GA)

I use one called 'GARDEN SPECIAL' 5-10-15 with Micronutrients, a blend made especially for vegetables. My iris love it and I have had NO black spot since using this. It comes from GROSouth, 255 Dexter Ave., Montgomery, AL 36104. Phone (334) 265-8241. I buy it in 40 lb. bags and use 80 lbs. for my 2000 plus iris. I fertilize in mid February here in 7b/8. You might get your local supplier to stock some of this. If you want to see what it does for my iris go to my web site.

Here is a link that might be useful: Mountaintopiris

    Bookmark   March 15, 2007 at 12:23PM
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Thanks so much for the detailed response. Just what I needed! I have talked with Grosouth in ALA today; they referred me to their Atlanta distributor who in turn directed me to the farm supply center nearest me who carries the fertilizer. It means a little road trip, but a reasonable one which will be fun.
Thanks again!
PS: I really enjoyed your website! Inspirational.

    Bookmark   March 16, 2007 at 10:49AM
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kittyl(8/9 Calif)

Your type of soil will likely have an impact on the result of applying fertilizer. No one size fits all. I have very porous soil, and I apply fertilizer and bone meal on the surface before the major growth starts, in Jan. and Feb. By the time the growth is well under way, the rains have soaked the components down to the root level. With clay soil, this will not work as well. One can also supplement with a water soluble fertilizer as a repeat application up until a couple of weeks before bloom. Fertilizer close to the bloom season can cause irregular growth in the stalks and what is called ÂsnakingÂ. But it doesnÂt hurt them. IÂm not too picky on the brand of fertilizer, I just stay away from high nitrogen for irises.

    Bookmark   April 1, 2007 at 1:57PM
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cbfindlay(z6 OH)

I was wondering about this topic as well. I just put down some cow manure compost, tried to work it into the soil, but that seems difficult with the roots so near the top... I was hoping this tactic would work. I only put down like 1/2" around each plant. Am I supposed to make sure that the compost does not cover the exposed rhizomes?
Cindy in Columbus

    Bookmark   April 5, 2007 at 10:46AM
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As a fellow Bloomingtonian and iris grower, I have to answer this, albeit a year late. Generally, I put a small amount of bone meal down every year along the roots of each plant in our clay soil. After three years of doing this or so, make sure you run a soil test as phosphate tends to accumulate in our soil. Also, make sure you do something for borers and have a fungicide handy for the leaf spot that inevitably will follow bloom (which comes reliably in May). Also, take solace in the fact that last summer was very unusual and that so far this year has been very, very normal. Finally, never, never put cow manure on your iris unless it has aged about 20 years or so and has not a trace of nitrogen left.

    Bookmark   March 9, 2008 at 8:39PM
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