Expert: Kenneth Joergensen - 1/1/2004

Question
I live close to Houston, TX.  We have had hardly any cold weather yet and want to move my iris.They have not done well where they are.  They have not hardly bloomed at all.  The rhizomes are not planted very deep.  Any suggestions on moving them and why they are not blooming.  I have had them several years. Thanks.

Answer
Bearded irises usually bloom reliably for three to four years but produce fewer and fewer blossoms in succeeding years. This is because their rhizomes increase each season until they eventually become overcrowded and starved for nutrients. Dividing these clumps and replanting individual rhizomes in freshly prepared soil gives the plants a new lease on life allowing them to re-gain their blooming strength.

Timing
Usually fall is best depending on your climate (In Texas September/October would probably be a good time). If you divide when the soil is still warm from summer but the air has begun to cool for the approach of winter, you will be replanting just at the peak time for disturbed roots to re-establish themselves without placing a severe demand on them to supply abundant moisture to the leaves.

If you have a mild winter it can also be done, but you risk a cold snap can interfer with the re-establishment of the plant. Warm soil, but cool air is the best for iris when dividing. I will leave it up to you to try and divide now or wait until next October.

Step by Step instructions:
1) Dig up the entire clump with a garden fork or split off individual rhizomes. Try to avoid damaging the roots or the leaves.

2) Remove excess dirt and dead material from the clump. Remove enough so that the clump is fully exposed.

3) Trim the leaves (called "fans") down to 4-6”. Trim in at an angle on each side. E.g. the top should look like pointed arrows (tee-pees).

4) Use a sharp knife to separate the rhizomes. Dip the knife in ten percent bleach after each cut. (1 part bleach to 9 parts water in a bucket. wear gloves).

5) The new transplants should have a firm rhizome with roots and a fan of leaves. Remove and discard the old rhizomes and only replant the younger smaller rhizomes that grow off of the older stems. Discard any rhizomes that are spongy, rotten, or have visible insect damage. The middle is usually the old rhizome and the edgers are younger.

6) If necessary amend the soil of the planting location with compost. So long as the soil is light your iris should do fine.

7) When planting iris, dig a hole about five inches deep. Build a small mound in the middle of the hole. Place the rhizome firmly on top of the mound and let the roots fall down over the sides of the mound. Cover the roots with soil so the rhizome is just slightly exposed. Do not plant the rhizome too deep or it may rot.

8) Pack firmly and water to settle the soil around the roots. Do not drown the plant, however.

Iris are light feeders. Top dress the soil with a complete N-P-K fertilizer (annual plant fertilizers or tomato fertilizers) in early February this year. In future years only fertilize about 1 month after flowering.

Good luck