Gardening with Gary

Gardening Advice from an Expert

Iris

Q. I live in St. Louis, Missouri, and I moved into an older home 2 years ago that has bunches and bunches and bunches of crowded iris plants. These iris have never bloomed since I've been here and the green leaves of the iris look about 1/2 - 3/4 fully grown now. My question is: Can I thin them out now at this time of year and replant them? And, just how do I thin them out and how deep do I replant them? I've never had iris before. Thanks for your help!

A. This is an unfortunate time to be considering such action, but as you say they have never bloomed, so what have you to lose? The iris have been neglected by the past owner [maybe they didn't like flowers...what?] So here is what to do:

Start at one end and using a good spade, dig around the green stems, keeping in mind that the rhizomes underneath are spreading out a ways, so do not cut in too close or you will slice into them. Make a wide circle around a group, lift them out and lay on paper or plastic. Only dig out as much as you will handle that day.

Gently shake off some soil, and observe where the underground growths have separations. Break them apart, so that all the new plants have roots and foliage. If a couple small ones are joined, do not worry...leave them until the fall or next year. Be sure to separate mainly the large ones which are joined.

Replant into the bed, which you have worked up with additions of dried compost or any organic material you have or buy. Space them 8 inches apart, having the rhizome just below the soil line. Planting too deep will give you absolutely no flowers. That is the key to success with iris! In the future, please do this task in late summer, early fall, so that you do not interfere with the spring flowering.

Q. I have some bearded iris that look healthy with great green leaves, but no blooms. They have never bloomed in 6 or 7 years. They get a lot of sun, but I don't fertilize them at all. I think this maybe the problem. The soil is sandy and doesn't hold much water either. Is fertilizing my problem? What would be a good fertilizer to use?

A. I have two ideas for you:

One is the depth of the rhizomes in the soil. Did you know if you plant them down into the soil that the irises will not bloom? Right!

The tops should be right at the soil surface. You can cover with a bit of soil or mulch to protect them from the sun rays, but do not have them completely down into the soil. The roots grow down and collect the needed moisture and food. If you planted them maybe 2-4" deep, they will not produce flowers unless the top soil erodes and the rhizomes are at the surface. Strange but true.

You know number two: Fertilize!

Plants are just like animals in that they need food to live and grow. I want you to start a regular fertilizing program with not only your iris, but all the plants you are growing, inside and out. Buy a good food from a garden center, like Scotts, Peters, Rapid Grow or Miracle-Gro. They all supply what plants need to produce good foliage and flowers. Sprinkle some bone meal around the iris now, give them food every three weeks until the coolness of fall sets in.

In the spring, just as the tiny sprouts are seen pushing up, start feeding again, every two weeks until the flowering is over.

Q. Do I need to deadhead my irises? And when?

A. All your iris should have been cut back by now [mid-July]. Here is what I want you to do:

Take very sharp and clean shears and cut the flower stems right back into the foliage. Do not remove the leaves, though. Discard.

Then, take the clippers and cut all the leaves, which are called blades, to one foot above the soil line. Trim them straight across, in a line. It can look quite attractive this way. The foliage will continue to produce food for the underground rhizomes, so that next spring you will have healthy growth and increased flowering.

Feed them once a month until cool weather sets in. A general 30-10-10 or similar makeup will be fine, one tablespoon per gallon water in a slow, deep drench. Do not allow the plants to dry this summer, and you can mulch them if you like. This retains the moisture and keeps the rhizomes and roots cool.

Q. I have a 3 year old iris plant (4 bulbs) that had only a few blooms this year. Is it time to dig it up and divide, as it does look crowded? I haven't fertilized it this year. Do you think that could be the problem? If I do transplant them, do I cut the leaves down? Is this the right time of year [early August] to do this, or should I wait until Fall?

A. Right now, I want you to trim all the blades back to 12", cut across in a straight line with sharp, clean shears. Water them well throughout the summer, especially when rain is lacking. Feed them by all means, now once a month. Give them a general gardening food as Rapid Grow, Miracle-Gro or Peters at one tablespoon per gallon water, in slow, deep drenches. You want the underground rhizomes to get the food and build up for fall.

Then, in early fall, when the soil is still very workable, dig up the clumps. Lay them out on paper or plastic sheets and shake off whatever soil you can [doing when a bit dry is useful]. Using a sharp, clean knife, cut and pry apart the various parts of the rhizomes [or as you say bulbs], keeping a root system with each part if possible. Do not fret if some have none. remove any yellow or brown leaves, but keep all the others intact.

Work up the garden bed with some peat moss or compost. Dig down about one foot. Replant the rhizomes at a space 12-18" apart. Lay the rhizomes on top of the worked soil and cover with just about 1" new soil. Water in well. Cover all the tops of the rhizomes if showing, but do not have deeper than one inch! Otherwise they will bloom sporadically next year.

Next spring, start feeding them very well as soon as you see sprouts popping up, every two weeks. By mid-spring, you will be blessed with quite a show!

July and August are very good times to renovate your iris beds. Carefully dig up the clumps and cut away the old center rhizomes that are no longer producing leaves and flowers. Use a sharp knife and dip in 10% bleach water to prevent bacterial infection. Rhizomes will be mushy and have a foul odor if not well. Throw these away, not in your compost pile.

Cut the leaves back to 6" and replant the rhizome pieces 8" apart. Be sure to keep them watered during when lacking rain. By fall and the dipping temperatures, the plants will be secure and ready for dormancy, plus will bloom all the better next spring.

Cora writes~ A friend gave me bulbs for a gorgeous dark red iris 2 years ago. Its leaves come up, but no flowers. I fertilize, but should I also use bone meal? If I use bone meal, should I do it fall and spring? I bought some and the box just says to put a teaspoon of the bone meal in the hole you dug for your bulb before you place it in. What about bulbs you already have in the soil?

A. First, I wonder about your fertilizer program. Are you using a good one with a high middle number on the label in the spring, just as soon as you see little growth popping up? And do you continue to feed well every week or two. I switch as the buds appear to Rapid Grow, since it has more nitrogen for the foliage and green growth needed after blooming to build up the rhizomes during the summer.

Go ahead and add some bone meal as directed. Yes, you can sprinkle it on top of the soil and water in, so it soaks down into the root zone. This can be done either now in the fall or later in the early spring, but I prefer now so that the roots can use it all winter and ready for blooms sooner. Cut the leaf blades back to about 6" after all the flowers are spent and removed, but keep watering and feeding all summer long, for the reason above.

Also, how is the light? They do best in good light, at least 1/2 to 2/3 day sunlight. If in a very shaded area, they will only bloom once in a while and all you will get is good green foliage!

Karen writes~ My iris did not bloom this year or last year. I planted them in the fall of 2000. What did I do wrong? I planted some of the same batch in other areas and they did wonderfully. What should I do?



A. How deep did you plant them...shallow I hope.

Did you mulch them...very little I hope, as that can lead to rhizome moisture and rot.

How cool does your area get...good winter climate is necessary fori very good blooming of many species.

Or, the pH level of your soil is not compatible to the plants' needs. Have your soil tested so you will know exactly what pH and other elements you have. Irises prefer a neutral pH (7.0). If your pH is high, your soil is alkaline and can be amended by adding sulfur. If your pH is low, your soil is acid and can be amended by adding lime.

Morning sun is the best and plenty of it. If shaded constantly, flowering will be sporadic. Afternoon sun is fine so long as they get a little protection from the very harsh summer rays and you watch their watering closely, all summer long! They need to grow good foliage until frost as this produces food in the rhizome which produces the flowers the next spring. Cut the foliage straight across at a height of about one foot above the soil. Remove any yellow or brown leaves to prevent infestation.

Do you get plenty of foliage increase and is it lush? If they get too much Nitrogen and too little Phosphorous, they won't bloom, despite looking good.

Give them a garden fertilizer for spring-flowering plants, one high in the middle of three numbers on the label.

They also need a certain amount of chilling in winter to set bloom. Certain varieties do better than others in the heat. Have a look around at your neighbors gardens and see if they have any blooming.

Mulching is OK so long as you keep the mulch back from the rhizomes so that they don't get wet and steamy. Coarse wood chips or a stone mulch are best.

Here is an excellent commercial iris site with lots of frequently asked questions [FAQ] to assist you and others:

www.argyleacres.com/faqs.htm

Carolyn writes~ What is the hardy zone of an iris plant? I live in Hawaii. Will the iris plant be able to take this warmer weather?

A. The German bearded iris may not be able to withstand the intense heat, humidity and amount of summer rainfall. Dutch iris may be a better route to go, but The Louisiana iris sounds like your best bet:

The Louisiana is the most adaptable of the iris family. No other species of Iris can grow so successfully in such a diverse range of geographical areas. They are happy to grow in naturally marshy or wet conditions, they can grow successfully in a pot in water and they are also just as much at home in an ordinary garden condition. They will tolerate extremes of heat and some cold provided they are mulched against those particular extremes of temperature. They are particularly happy growing in areas which receive considerable summer humidity. This trait sets them apart from the bearded iris varieties, which tend to struggle in these hostile conditions. You can grow Louisiana iris in the garden, in pots, in a pond, in a rockery (to protect the rhizome from extremes of heat or cold) or let them go wild by the side of a dam or water feature. They will adapt quickly to their new environment.

http://www.louisianas.org/cultivars/culturalreq.html

The best time to transplant Iris is 2-3 weeks after the finish of blooming. Dig the clump up and pry the rhizomes apart, discarding all shriveled and diseased parts. Stalks which produced flowers this year will not produce again. However they provide food to the new side shoots which will be next summers bloomers, so be sure to leave these new shoots attached to the mother. Cut the leaves back to about 6-7 inches.

When replanting, be sure to dig in a good granular bulb food into the soil. Dig a hole of ample size for root development and mound the soil in the center so that the roots may be spread over the 'saddle'. Barely cover the rhizomes with soil. For multiple plantings in the same hole, arrange the rhizomes so that the leaf-ends point away from the center and plant 8 inches apart.

From my files, This is a good hardy zone map for your state:

http://www.thegardenhelper.com/hawaii.html

Joy writes~
Should I cut my iris plants down now that they are finished blooming? And is it better to plant new plants/bulbs now or wait until fall?

A. All spring flowering plants need growth to build up the food supply underground for the long winter they fave. For iris, use sharp, clean shears and cut the green blades straight across leaving about 8-10". Cut off any yellow or brown blades and discard. Keep these plants well watered throughout the summer and feed them at 1/4 strength garden fertilizer every two weeks. The longer they stay green, the more food will be stored. This will result in larger and greater amount of flowers next spring. Same general directions apply to daffodils, narcissus and tulips. Loosely tie the green stems, flowers and seed pods removed, with garden twine. Keep foliage green as long as possible but remove any poor leaves. Cutting off all foliage right after blossoming reduces your flower production the following year.