CULTURE FOR JAPANESE, BOG, WATER AND SPECIES BEARDLESS IRISES
BY POLLY KINSMAN
Culture is for the most part the same for any of the water loving irises. Japanese, Pseudacorus, Virginicas, Pseudatas, etc.
All are easy to grow. The most important factor is they must be kept moist the first year planted. After that they will do well with less water, but will thrive with more.
The irises will do well in most garden soils, but for strongest growth additional water is recommended. Especially up until bloom time, and in the late summer, which is when root increase is great. Extra water will increase height of plants and size of bloom. Most of the water irises can be grown in or near a pond, but in areas that freeze they cannot have their rhizomes under water as it will suffocate the plant. If you wish to grow them in a pond, in a cold climate, put them in a pot which you can take up and sink in the ground over winter.
These irises prefer a heavy rich soil, on the acidic side. Manure or peat is a great addition to the soil before planting. Be sure the manure is aged, otherwise it may burn roots. If the PH is too high, you will notice a yellowing of the leaves. This can be corrected by watering with Miracid until the irises are divided, then add agricultural sulfer to the soil. (Be aware, some of the Japanese X Pseudacorus AKA Pseudatas have intrinsic yellow leaves, especially in spring—nothing is wrong with them).
Plant divisions of three to four fans. Never allow the irises to dry out while planting or transplanting. Soak the roots in water before planting for up to 2 days. Plant the rhizome 1-3 inches deep, and in a depression of 3-4 inches, which will help hold water. Mulch heavily. Oat straw is an excellent mulch, as is pine needles. Pine bark is good as well. These irises grow their new rhizomes on top of the old rhizomes so putting them in deeper allows them to stay in the depression longer before needing to be divided.
Divide plants in the early spring, or late summer to early fall, being sure it will be cool, and you can give them enough water for a month after dividing. Plant divisions 18-24 inches apart. New information suggest not planting irises back into the same place, as the new info indicates the Japanese iris might posion the soil, however we have had no trouble with this. My personal belief is that the Japanese irises deplete the soil, not poison it. It makes sense to me, as they are such heavy feeders, that they will quickly deplete a soil. Amend the soil well at time of division. Plants grown well will need to be divided every 3-4 years. If the center of the plant is dying out, that tells you division is needed..
Japanese and other water irises are heavy feeders. A balanced fertilizer such as 10-10-10 in the spring and right before blooming works well. A watering every two weeks of Miracle Gro, (alternating with Miracid if you see any leaf yellowing) is great. It is hard to overfeed or overwater the water irises.
Japanese irises have a tremendous root growth period in the late summer/ early fall. For that reason, I like to be sure to Miracle Gro them right up until ground freeze. They may get new top growth. That won’t hurt them a bit. It does NOT make them weaker going into the winter.
Most water irises have little or no pest problems. Thrips or iris borers can be controlled with a systemic insecticide.
WHEN YOU RECEIVE JAPANESE, OR MANY OF THE SPECIES IRISES IN THE FALL, THEY MAY HAVE SOME BROWNING ON THE LEAVES. THIS IS NORMAL. SOME CULTIVARS START TO GO DORMANT EARLIER THAN OTHERS. NOTHING TO BE CONCERNED ABOUT.