Iris Planting, Feeding, and Care

Preparing the planting hole when digging and dividing your rhizomes

You might notice that the bloom of your prized irises begins to decrease in vigor and quality. Irises are heavy feeders of the soil's nutrients and are competing for what little nutrients remain. Digging and dividing irises are the solutions to poor bloom problems.

July and early to mid August are the months to transplant and/or divide iris in the Prescott area. For the best bloom, it is recommended that iris clumps be divided every 3 years. Dig up the clumps with a shovel or other similar tool. When dividing, break off rhizomes from each other and replant only the largest fans. Throw out rhizomes with old blooms stalks. If you want, trim the fans (leaves) to 4-6 inches to prevent them from blowing over.

Make the holes at least 12-14 inches around and no closer than 18” apart. Closer planting will result in dividing clumps more often than every 3 years. If replanting a large clump, dig a hole the size of a tire rim.

Remove the dirt and the rocks. Rock removal is easily accomplished with a box screen made of hardware cloth (wire mesh). Then mix the dirt with 50% Forest Compost (available at Mortimer’s Nursery, Lowe’s Garden or Ace Hardware). Place the mixture back into the hole and fill hole with water; this will settle all air pockets.

In a day or so when the soil can be packed down without getting your hands muddy then plant the irises. Remember not to plant if the soil is still real muddy; as the iris will settle too low. You should be able to pick up the moist but not soggy soil and have it fall through your hands.

Add a tablespoon of bone meal, and a tablespoon of cottonseed meal; mix well with the soil. Do not use any more than that. Plant the rhizome with the top exposed to the sun, roots face down in the hole. Pack the soil firmly around the roots. After planting, use all purpose balanced fertilizer such as 10-10-10 with nitrogen 10 or less. Applying a root stimulator is also beneficial.

Water well and let the soil dry out between each watering. Water 2-3 times a week unless we get a good rain. The goal is to encourage growth as indicated by new leaf production. This may take 2-3 weeks. Once new growth is well established, water 1 to 2 times per week. The rhizome needs time to root before the first freeze which could be as early as September 15th in the Prescott area and it takes a minimum of 3 weeks to root. Frost occurs a few weeks later in the Verde Valley or Yarnell area.


Potting iris from the PAIS Rhizome Sale or received through commercial growers in the mail. The only common bulb iris is dutch iris, which this site will not address.

Potting rhizomes which have been out of the ground for a while will help insure that they root faster and grow vigorously once planted in ground.

  1. It is best to pot the iris in one or two gallon pots first, that way you’ll be able to keep your iris moist and can check on how much water they are getting. Use 50% natural soil and 50% forest blend compost. Stay away from compost that has cow and/or chicken manure in it. Compost with horse manure is ok. Good compost is essential to starting root development. Get the irises off to a good start with 3 -4 tablespoons of unsulphured molasses to one gallon of water plus liquid plant food with 2-15-15 or 8-16-8. Remember the irises need to get a good root system started before the first frost. Now prepare the planting beds. It takes around 3 weeks for iris to develop roots. By using pots you not only save water, but you can use less of the compost mixture. Once fans start to appear, the irises are ready to be transplanted into the prepared beds.
  2. If you dig the irises and don’t have time to replant them immediately, you can pot them until you are ready to plant. Remember to harden them off first. Harding them off means that after you dig them, wash the dirt off the roots, mark a leaf with the name of the iris, trim the roots, then set them in a cool place for three to five days. Once you dig the irises up, the roots die, so don’t think you can save them. They will need to dry.
  3. When digging an iris clump that does not need dividing, but just transplanting, if you keep the dirt ball on the roots, you may be able to plant them immediately in the newly refurbished soil without trimming the leaves or the roots. Be sure to water well.

Alfalfa the Magic Elixir

Alfalfa, like many other forms of compost, adds humus to the soil which enhances plant growth in almost any type of soil from the acidic rain leached soils to the sandy, granular, alkaline soils of the arid desert. What makes alfalfa special is a chemical called Triacontanol which is a growth stimulant. When any form of raw vegetative matter is added to the soil, decomposition occurs which generates heat. Warmer soils, relatively speaking, would stimulate root growth. Also fermentation of vegetative material generates alcohol, another growth stimulant. Alfalfa is readily available from local feed stores in several forms. Meal is a finely ground powder form. Rabbit alfalfa food is a compressed palletized form expands dramatically when wet. Horse cubes are coarsely compressed into 2” squares. The meal or pellets are easiest to work with. They come in fifty pound bags.

Consider adding alfalfa to soils annually at transplant time and rototill it 6-8 inches down into the root zone. The plants seem to establish a new root system very quickly and do not put up top growth. Since the value of most compost is used up within the year, an annual application is important. It can be added as top dressing or applied as a soil drench as “alfalfa tea”. You can apply a handful of alfalfa meal around the base of reluctant spring starters which seems to be a benefit before bloom time.

Alfalfa Tea Recipe

  1. Choose the size of container and make sure it has a tight fitting lid.
  2. Use 4 cups of alfalfa pellets or alfalfa meal to every 5 gallons or 20 liters of water. Make sure the alfalfa has no salt, corn or molasses added.
  3. Add ¼ to ½ cup Epson salts (magnesium sulphate crystals) to every 5 gallons of water used.
  4. Fill with water, put on a tight lid to prevent mosquitoes from breeding in your swamp.
  5. Let stand for about a week in a warm out of the way spot in the yard, stirring daily until it bubbles with fermentation.

You can then apply the liquid to your iris beds once every couple of weeks. The left over alfalfa mush at the bottom of the container can be worked into the soil as organic matter.

Iris Rhizome Soft Rot

It happens once in awhile to everyone who grows irises. A fan will fall over; its base has turned mush and stinks. Left unchecked, this bacterial rot will destroy the entire clump. It requires immediate action. Here are two recommended courses of action.

  1. If the rot is confined to one part of a clump, you may have good luck with just cutting out the affected parts, back to firm, white rhizome, and liberally dusting the wounds with Comet or Ajax cleanser or some other chlorinated cleaning powder. The chlorine disinfects, and the powder acts as a drying agent too. Leave the newly cut rhizome exposed to air for several days.
  2. If the damage to a clump is extreme or if the soil is still very wet around the clump, it is better to life out the clump. Carefully cut the infected rhizome out of the clump and discard it. Then disinfect the rest of the clump by drenching it with a solution of one part bleach to nine parts water. Follow this by dusting the clump with Comet cleanser. Let it dry for a day or two and replant in a drier location, if possible.

The Iris Transition (Spring to Summer)

So, bloom is over and what happens to your iris plants during this transition period before July? Actually, this is an interesting question and the answer helps explain why irises are transplanted during July and August in the Prescott area. Bloom in the Prescott is just about finished by the end of May and all that energy in the form of starch that was stored in the rhizome has been used to form bloom stalks as well as causing an overall increase in leaf growth and enlargement.

Do irises go through a period of dormancy after bloom? A number of irises writers say this is so. Actually, irises are not “dormant” but rather changing the growth pattern from one of bloom (May) to that of plant enlargement and the beginning of new fan development from the rhizomes. The larger the rhizomes and leaves, the more successful this new fan development will be. Smaller, less vigorous plants will produce smaller new fans. Last years new fans developed during this period begin to grow as these fans are the ‘chosen ones” and possibly will bloom next year. In our environment you have to water the plants regularly and add fertilizer around each clump.

Care of Iris Timeline


  1. Preferred time to add bone meal and only a small amount per plant. Scratch it into your soil, water well and do not get any on your rhizome.
  2. Fertilize in March, use granular, low nitrogen fertilizer such as 10-10-10. Sprinkle about 1 cup per clump. Keep granules off the rhizome.
  3. Water deeply every week to ensure good growth and bloom.
  4. Keep after those grasses and weeds.
  5. Pick off dead flowers after stalk has bloomed.
  6. Enjoy the bloom, Invite friends over; share the joy of spring.
  7. Take photos of your blooms for your own documentation and for the rhizome sale.
  8. Double check correctness of variety on plant markers. Go to internet and search by name of iris for photo of your flower to verify it is correct. A good place to search is the AIS Iris Wiki which will have an accurate description and a photo of the bloom.
  9. Update your iris notebook with bloom information and culture notes.
  10. If your varieties are starting to grow together, tie a string around the base of the clump to separate clumps so you will know where to dig in the summer.
  11. Begin thinking about which iris you will be dividing that are getting too crowded.


  1. Break off all spent bloom stalks to the base of plant. Leaving the stalk will take nourishment from the plant.
  2. Give your iris a feeding of neutral fertilizer, either granular or foliar such as 10-10-10. If growing rebloomers, consider feeding them Triple Super Phosphate to encourage the next bloom cycle.
  3. Any mystery iris that were not true to name can be dug and given to someone who doesn’t care about the named iris.
  4. Plan what your next beds will look like.
  5. Make a list of iris clumps you will dig and donate to PAIS.
  6. Watch for sales on potting soils, fertilizers and topsoil. For maximum bloom replenish soil every 2 years in the iris beds.
  7. Look for decorative additions to your garden.
  8. Keep your beds weed-free and be on the lookout for grasshoppers, aphids and thrips.

Fall Iris Culture

  1. Continue watering deeply every 7 to 10 days. This encourages the development of the fans and the continued growth of the rhizome.
  2. Keep your iris beds free of dead leaves and weeds.
  3. Do not cut the leaves back as this will decrease the starch production in the rhizome. When the leaves die, pull them off.
  4. When pulling off the dead leaves, make sure the tips of the rhizomes are not covered with dirt. After rain and snow, the rhizomes tend to get buried deeper.
  5. Also be on the lookout for soft rot and treat the rhizome immediately. As you are doing your fall cleanup, remove dead leaves and sniff their base. The scent should be earthy. The slightest smell of rot means it is time to take action before any visible damage occurs. Use Comet or Ajax cleanser on the rhizome to dry it out. Sulfur is another source for drying out the rhizome. See further explanation under “Iris Rhizome Soft Rot”.
  6. Check plant markers for placement and legibility. If they are faint now, it will only be worse next spring.
  7. Make sure your iris map is up to date. Markers frequently get dislodged during the year. An accurate iris map will help you replace the markers correctly.


  1. Water deeply about once per week beginning in January unless we have an exceptionally wet winter. Let soil dry out between each watering.
  2. Gently remove dirt from the tops of the rhizomes. When the dirt is moist use your fingers. It is important to remove the dirt so the rhizomes can dry out and not rot because of our freeze and thaw cycles.
  3. Fertilize in late February or early March. Recommend utilizing “Bayer Systemic Rose and Flower Care” either in granules or liquid to prevent insects such as Aphids and Thrips. If no sign of insects use a multipurpose food such as “Arizona’s Best All Purpose Food 10-10-10. Be sure the first number which is nitrogen is 10 or lower in the fertilizer you purchase.

The Lowdown on Compost

Reprinted from March 2007 PAIS Newsletter, by Barry Golden

Composting depends on having something to break down, adequate water to wet the mass, and a plastic cover to cover your pile. You don’t need fancy/schmanzy compost starters. Find an area of your garden that is fairly level and start piling leaves, grasses, weeds (omit those weeds that have gone to seed) and kitchen scraps like vegetables (no meat). As one adds materials, just sprinkle the mass lightly with water. Try not to soak the pile, but if you do, nothing bad will happen. Just do it!

Add some form of manure, like horse manure, to get the pile composting faster. This is all about bacteria, fungi, yeasts, worms and other insects that will use the pile of material for their nutrients to grow and reproduce. Your pile should get hot from the energy released from bacterial growth and reproduction. Never underestimate the power of microbes like bacteria. The bacteria need water and adequate nutrients to grow. Turning the pile with a shovel every month or so will help the bacteria grow. Many of these composting bacteria need oxygen and that is why you turn the pile every so often to aerate the pile. Cover the pile with a plastic tarp to retard water loss, but you can cover the pile with anything available, like plywood.

Some other Iris Care links