Fertilizing Irises

What methods to you recommend for fertilizing iris? I once heard that one should dig in a balanced garden fertilizer after the bloom finishes. Is this what those of you who grow a lot of iris do?

The best way to fertilize any plant is to start with a soil analysis of your garden soil. That's really the only way to determine what, if anything, your soil needs to provide optimal nutrition to the plants you wish to grow. Overfertilizing can be as damaging to your plants and soil as can underfertilizing, so you need to know what you're starting with.

That said, there are some general guidelines relative to bearded irises. Beardeds should not be fed high nitrogen fertilizers or amendments. Nitrogen promotes rapid, soft growth that is particularly susceptible to bacterial soft rot infections and freeze damage. Although irises do need some nitrogen, too much can be problematic, esp. if applied later in the growing season when it will promote tender new foliage that may be damaged by early frost. Nitrogen leaches out of the soil quickly, so it may be advisable to apply a fertilizer with a higher nitrogen content in sandy or otherwise fast-draining soils or in areas of heavy rainfall.

Phosphorous helps promote bloom but can poison both your soil and plants if applied in excess. The same holds true for potassium. Neither element leaches readily through soil, so if you overapply them, you'll have a problem for a while.

Many people apply a low nitrogen fertilizer in early spring about 6 weeks before bloom and then a no nitrogen fertilizer sometime after bloom.

Laurie

This message was edited Jul 29, 2006 2:36 PM

Thanks so much! In the past I haven't fertilized my irises at all, but they would probably bloom more if I did. The advice on the timing and nitrogen content are especially helpful.
I have been putting off doing a soil test, but will now do one. I already have the instructions from the county agent. I think all of my plants would benefit if I did have one.

Hi Pajaritomt

I fertilize my iris 3 times a year with a 10-20-10 garden fertilizer, I only use super phosphate starting in Febuary,
every one of my iris bloom & also get a bag of just potash & use extra of that to help make the iris more winter harder in my climate, I used to have a lot of winter kill, untill I started the extra post ash.
If you have a co-op around you, you can buy a 40 lb
bag of garden fertilizer & it can also be used on everthing else.

I don't know of a coop, but I am glad to hear that you fertilize them 3 times a year. It seemed pretty hard to never fertilize them except with phosphate after they bloom. I have been using bone meal with everything I plant. If I use a lot of it, will it be as good as superphosphate?
I have never had winterkill. I have heard we have a lot of potash in our soil. Do you still think a little extra will help?
Betty