Sunday, June 10, 2012

 Hi iris lovers, Tim, the owner/hybridizer over at Beaumont Ridge Iris was kind enough to allow me to post this information about how and when to fertilize your irises.  He has spent quite a bit of time and resources researching this subject. Now this is a man who loves his iris!  Thank you Tim!  I really enjoyed reading this as well as learning more about my lovely irises, and thought I'd share this info so that everyone else could give their irises the love that they deserve.   &:-)

From his post last April:


Fertilizing time -- using 16-16-16.
But before all you irisarians start commenting on the excess nitrogen content, this special formulation is a dual release nitrogen -- 8% readily available, and 8% slow release sulfur coated ureaform.
So, it feeds for a long period of time, and my plants don't lack for the basics at any time during the crucial growth and bloom development phase. What most people don't know is, that bearded iris use nutrients in different ratios according to the time of year it is. Deciding factors are daylength, and nighttime temps. During the initial spring growth phase, bearded iris use nutrients at a 1:1:1 ratio.
After bloom, they start using nutrients at a 1:2:2 ratio, and by fall it becomes a 0:2:2 ratio. The key is the keep the AMMONIACAL (NO-3) nitrogen low, the slow release (NH-4) can be considerable higher. My plants get two feedings a year. The first is a 16:16:16 which is now, and the second is a 6:20:20 in early June. I also use 1 20lb bag of IRONITE per 60 lbs of all purpose for minors which are absolutely essential to nutrient synthesis for iris.

When asked about how he came about this information about the ratios for nutrient uptake at different points in time during the growing season, this is what Tim says:
 For many years I was curious about the proper way to feed bearded iris, and the traditional 5-10-5 regimen so often recommended didn't seem to produce quality plants that suited me, even in what seemed to be fertile soil. So back in 1988, I started experimenting with different fertilizer formulas on different test plots, using the same plant "Titans Glory" as a subject. I noticed that all of my test subjects grew fairly well early in the season, but then as bloom season approached, I began to observe marked differences in plant performance, and I noted that the subjects with a more balanced nutrient formula, (split slow release/quick release) had a slower but longer growth curve, rather than the quick explosion of growth using conventional fertilizers that had ammonium nitrogen in them and then a quick falling off. I also was wondering why leaf growth slowed in the summertime, when the same ration of nutrient application was present.
Then I had a chemist friend of mine take leaves from my test subjects in early March, Mid May, and early July, crush them up, and then analyze the nutrient components present in the leaves. It was then that I found out, that the NPK ratios present in the leaves was markedly different at various times of the year. The springtime being a near 1:1:1 percentage of NPK present, and then 1:2:2 during bloom, and then roughly a 0:2:2 in the late summer. The rhizomes of the test subjects were also macerated and analyzed with a similar result.
I'm not sure how my "findings" would stand up to a more detailed study and analysis, and I'm not a soil scientist, but I've tailored my feedings, and nutrient formulas that I provide my plants based on observations since 1990, with superb results. So I guess the simple answer to your question is years of trial and error, and experimentation -- with a helping hand from a chemist friend.


*** footnote :  NPK = Nitrogen, Phosphorus, Potassium... common ingredients in  most fertilizers

No comments:

Post a Comment