Expert: Kenneth Joergensen - 7/15/2004

Question
I live in Minneapolis MN 55419.

I have some plain purple iris that I need to move.

When is it best to transplant iris?  I would like to wait til early fall if possible.

Any special instructions for this?  I.e., whether or not to cut them back, whether or not to feed them some bulb fertilizer?

How far apart should I plant them?  I am a little low on space.

THANKS

Answer
I am not quite sure what type of iris you have, but I persume it is the tall bearded iris ?

Most iris plants do best if transplanted in july or early august so they have at least 3 good months to grow before the soil temperatures get too cold for root growth in late fall.

I would cut the foliage back to about 6" from the ground. The cut foliage is also sometimes called "fans" (because they make a fan shape). Dig the clump up with a shovel. Make sure to get in under the clump and use the shovel to lift it.

If you want, you can divide the clump (e.g. instead of one large clump with several stems you can divide them into smaller sections, or divisions, with fewer stems). This is how you propagate iris. e.g. make more plants.

Do this by cutting through the hard material between the roots and the green foliage. This material is called the crown, or rhizome. Make sure that each division have at least 1 fan (one set of leaves) but 2-3 sets of leaves per division is fine, too.

Plant them shallowly covered by one 1-2" of soil. Too deep and they wont flower. Make sure the soil where you are planting is very well draining. Plenty of organic matter such as compost and some builders (not playground) sand mixed into the soil is preferred.

I would plant each division 12-18" apart on center.

I would not fertilize them now, but next spring apply a slow release fertilizer (e.g. bulb fertilizer, annual plant fertilizer, or tomato fertilizer) around the base of the plant.

When you dig the plants and are going to divide them, if you find that they do not grow from a central crown (rhizome) but instead are small individual bulbs (scallion size) then you have a different size of iris. Just plant the individual bulbs 3-4" deep about 3-6 bulbs per sq foot. These are also commonly called dutch iris. They are not growing from a rhizome but from an actual bulb.

A rhizome is no more than a fat root which has ballooned to store the carbohydrates needed for next year's growth. This structure is somewhat different than a true bulb. But you will see it when you dig them up. If in doubt, rinse off the dirt with a gardenhose before trying to divide.