Irises prefer a full day of sun, but will grow and bloom well if given six or more hours of sunlight. The best time to plant is after the Iris has finished the bloom season and before it starts new growth. In most cases, this will be between July and October avoiding periods of temperature extremes. The ideal time is when the summer heat has ended and cooler fall weather arrives. For climates with severe winters and early freezing temperatures, we recommend planting prior to August 15. This will ensure early root development. The bearded Iris is drought tolerant but will rot if too wet. Gardeners can avoid many problems by providing good drainage to protect the Iris from getting "wet feet".
When you receive your shipment of Irises you should remove them immediately to let them air out for a day or so before planting them. If you are unable to plant them within a day or two lay them outside in the shade. Do not put in a closed building where they might get too hot. Irises can remain out of the ground for a week or two but you should try to plant within three days of receipt. Water at planting time and keep moist but not soggy for the first month (see About Sunlight and Water section below).
A well-prepared bed for your Irises will result in better growth and bloom. Irises grow in average garden soils with a PH close to neutral (6.5 to 6.8). They like loose well-drained soil since they do not tolerate standing in wet soil. In heavy clay, we recommend raised beds or raised rows with lots of compost. Some say that adding coarse sand is good, but you will need to add at least 30% or you run the risk of creating concrete. We have had very good results with compost but, as with the sand, it takes a lot. Irises love compost but not too much green (compost with high nitrogen content). Although the Iris needs nitrogen, too much in the wet seasons will promote rotting. You should add compost to your bed as well as extra food (fertilizer) to promote the very best growth and bloom of your Iris. For new planting, well-rotted manure or well-rotted compost are good additions. A no nitrogen chemical fertilizer or super phosphate (or bone meal) can be dug into the soil at the rate of 1/2 ounce per square foot three weeks before the plants are set in. If adding at time of planting use 1/2 strength. It is best to double dig or rototill your Iris bed to ensure the mixing of the fertilizer and compost before planting your Irises.
Now that you have your beds ready in a sunny location make a shallow hole about twice the size of the rhizome. Take a handful of the soil you removed and make a mound of soil in the center. Place the rhizome on top of the mound and drape the roots down the sides of the mound. Press the rhizome down to ensure that it makes firm contact with the soil. Any air pockets can collect water and cause rot. When you fill the hole with soil the top of the rhizome should be at or slightly above the surface for warm areas and slightly covered for areas with freezing winters. Remember that it is always better to have the rhizome too high rather than too deep.
In our viewing gardens we plant the Iris in groups of three, forming a triangle with the toes pointing into the center. The toe of the Iris is the opposite end of the fan (the Iris leaves). The spacing we use is 12” apart, with 18" to 24" between each group of 3 rhizomes. If you prefer to plant in rows, you should space the Iris 18” apart and all facing the same direction so rhizomes will increase in the same direction without crowding each other. Be sure to water your Irises well after planting them. It is a good idea to record the name and location of your Irises. When they bloom your friends will surely ask for their names.
In cold winter areas, mulch before it snows. Use straw or comparable material, but not with grass clippings as they compact too much and they promote rotting. Remove the mulch after the last hard frost is expected in your area to prevent rot from forming when the ground warms up.
Irises do best in full sunlight but will do well in slight shade. That is to say, they should have a good six (6) hours of sunlight a day. In areas of extreme heat and little water, some shade is good. There are three times when the Iris needs water. When the Iris is first planted until the roots have taken hold. At this time the soil should be moist but not waterlogged. You will know when the roots have taken hold by the new center leaves coming up. This usually takes 2 to 4 weeks. Once established you should reduce the watering until the winter or fall rains set in. During dry spells (over three or four weeks long) you will need to give them a good deep watering every 3 to 4 weeks depending on the temperature. The second time the Iris needs water is in the early spring. In almost all areas, “Mother Nature” will take care of this for you. In a rare case that you have no rain or snow and hot temperatures in the spring season, you should supplement the watering every other week. The third time is for the reblooming Iris. They will need more water in order to develop stalks and flowers in the summer and fall seasons.
Irises should be fertilized in early spring about 6 to 8 weeks before bloom, and again after the blooms are gone. Because phosphate is important, we recommend bone meal or super-phosphate and a light balanced fertilizer such as 10-10-10 or 6-10-10 depending on the amount of nitrogen in your soil. The most important part is to not use anything high in nitrogen as nitrogen promotes rot problems. We highly recommend that you test your soil. Soil test kits can be purchased at most hardware or garden supply stores. What you want to see is neutral PH (6.5 to 6.8), medium to low nitrogen, high level of phosphorus, and medium level of potassium. All fertilizers will list the amounts of nitrogen, phosphorus, and potassium on the container in that order. For example 5-10-15 tells you that the container has 5% nitrogen, 10% phosphorus, and 15% potassium. Nitrogen is for the green growth such as grass. Your grass fertilizer is probably 25% or higher in nitrogen. Don’t use it on your Iris! Phosphorous promotes root development and since the rhizome is all root, it needs lots of phosphorous. Potassium improves the overall health of the plant, defends against diseases and helps plants withstand very hot or cold weather. In the fall it is a good idea to add bone meal or super-phosphate or both or fertilizer with no nitrogen such as 0-10-10.
Irises are very hardy plants and really do not need a lot of attention. Keep your Iris beds weeded and remove old dried leaves. This will provide air circulation. After blooming, cut the flower stalks as close to the ground as possible. This will help the Iris to concentrate its energy in new growth production.
We recommend dividing your Irises after about 3 to 4 years as they become too crowded. The Iris needs room to grow new plants. If over crowed, they will be unable to divide and the bloom will suffer or stop. Over crowding also promotes disease problems from lack of air circulation. The best time to divide your Irises is about 6-8 weeks after bloom season, usually in July or August. Clumps can be thinned by removing the centers of the clumps leaving the newer growth in the ground or by digging the entire clump and saving the new rhizomes and discarding the old “Mother” plants or any rhizome that is not healthy or is soft. It is a good idea to keep all your plants carefully labeled when removing the entire clump. You can use a waterproof marker to write the name on the leaf of the plant. After digging your Irises, divide them by cutting the newer rhizomes with fans attached.
Above is the textbook guide to planting and maintaining your Iris. The truth is, the Iris is a very tolerant plant. When we purchased our ranch we were given about 500 Iris to line our 600-foot driveway. At the time we were remodeling the 100+ year-old house and had very little time to spend on the Iris planting. As it turned out we did very little in following the “correct” way to plant Iris rhizomes. We did not plant the Iris for over three months and were not sure if they were still alive when a family member volunteered to plant Iris rhizomes for us. The area we had to work with is in the foothills and is almost 100% clay soil. We did nothing to amend the soil, just dug a trench with the garden tractor and put the Iris in the trench and kicked and pushed the dirt over the Iris. The driveway is eucalyptus tree lined without the required 6 hours of sunlight. Besides that, nothing is supposed to grow under a eucalyptus tree. I think that first summer we only watered once, even in the months with temperatures in the high 80’s. Later in the summer I purchased some Iris from the local hardware store (you know, the kind in little bags that are dried out and take years to flower) and planted them myself knowing nothing of how to properly plant them. About the only thing I got right was to put the roots down. I planted them in an extremely wet area (a bog really) during the rainy season and I planted them way too deep.
So what happened? We now have a beautiful Iris lined driveway. Although the Iris took an extra year to bloom, we lost almost none to the lack of water, and only a few to gophers. We lost about half of the Iris I planted in the wet area, some due to root rot and others that never established due to the poor quality of plants. The point is, that the Iris plant is very tolerant of abuse, drought resistant, and, by the way, they are deer resistant!
If you have any other questions about your Irises, please feel free to E-mail us: firstname.lastname@example.org, and we will gladly answer your questions relating to this bearded iris planting guide and iris gardening guide or any iris planting questions you may have about our gardening guide.