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Learn about Iris

Iris:  Perennial Bulbs and Bare Root Plants

How to Plant

Planting Bulbs in the Garden in Fall:

  • Plant when you receive the bulbs in fall. 
  • Success with bulbs depends on good soil preparation. Select a site in full sun to light shade with good drainage where water does not stand on the surface after a rain event. Bulbs thrive in well-drained, moist soils. Mulch the soil to protect the bulbs from the heat of strong summer sun. 
  • Dig the soil to a depth of at least a few inches deeper than the recommended planting depth. Work in organic matter to improve drainage, and at the same time improve the ability of the soil to retain moisture. A moderate amount of a balanced fertilizer such as Bulb-tone may be incorporated into the soil at this time. Mix the fertilizer into the soil so that it does not come into direct contact with the bulb.
  • Dig holes spaced 4-6 inches apart and plant Iris reticulata bulbs 3 inches deep and other iris bulbs 4-6 inches deep bulbs inches deep in ground. The general rule of thumb is to plant three times as deep as the bulb’s vertical diameter. 
  • Plant the flat part of the bulb down and the pointed part up.
  • Thoroughly water and apply a light mulch layer on top of the soil (1-2 inches) to conserve water and reduce weeds.

Planting Bare Root Plants in the Garden:

  • Select a location in full sun with good rich well drained organic soil.
  • Dig a shallow hole 2-4 inches deep and twice as wide as the rhizome.
  • Make a small mound in the middle of the planting hole. Place the rhizome on top of the mound and spread the roots on both sides.
  • Fill the hole with soil and firmly tamp around the rhizome but only partially cover the rhizome.
  • Water very well to fully saturate the roots and the soil.
  • Wait until new growth starts to appear before applying a layer of mulch.



How to Grow

  • Apply an organic bulb fertilizer when the plants emerge in the spring.
  • Keep weeds under control during the growing season. Weeds compete with plants for water, space and nutrients, so control them by either cultivating often or use a mulch to prevent their germination.  
  • Mulches also help retain soil moisture and maintain even soil temperatures. For perennials, an organic mulch of aged bark or shredded leaves lends a natural look to the bed and will improve the soil as it breaks down in time.  Always keep mulches off a plant’s stems to prevent possible rot.
  • Remove and discard foliage after it dies back.  


Growing Tips

  • Iris is easy to grow in beds and borders. The small spring bulbs also work well in rock gardens. For the best visual impact plant iris in masses.
  • Iris makes a fabulous cut flower.

Common Disease Problems

Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures. The disease may also affect and disfigure flower heads. Burpee Recommends: Remove infected plants. Avoid overhead watering. Do not work around plants when they are wet. 

Botrytis: This fungus causes a grey mold on flowers, leaves, stems and buds. It thrives in cool wet weather conditions. Burpee Recommends: Remove affected plant parts, avoid watering at night and getting water on the plant when watering. Make sure plants have good air circulation. Contact your Cooperative Extension Service for fungicide recommendations. 

Ink Spots: Tiny spots or streaks appear on leaves. The spots enlarge and become dark reddish brown. Spots may have grey centers. During wet weather masses of dark spores form in the spots. Leaves turn yellow ad die. Heavy infections can rot bulbs. Burpee Recommends: Remove and destroy dead leaves and debris. Remove and destroy any infected bulbs. Contact your Cooperative Extension Service for fungicide to protect plants. 

Root Rots: A number of pathogens cause root rots of seedlings as well as mature roots. Burpee Recommends: Practice crop rotation and do not plant related crops in the same area for several years. Pull up and discard infected plants. Make sure your soil has excellent drainage. Contact your Cooperative Extension Service for recommendations. 

Rust: A number of fungus diseases that rust colored spots on foliage and stalks. Burpee Recommends: Remove infected plant parts. Contact your Cooperative Extension Service for recommendations. 


Common Pest and Cultural Problems

Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps who feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap. 

Bulb Flies: Adults are hairy flies that resemble small bumble bees. They are blackish to dark green with pale yellow, orange or gray markings. The adults hoover around blooming plants, feeding on pollen and nectar. The larvae are plump, yellow, gray, white or brownish maggots with a short brown or blackish breathing tube at their rear. The larva infests the bulbs, causing yellow foliage and stunted plants with distorted and small leaves. Blooms and small bulbs often die. Maggots often enter bulbs through injuries or cuts into the bulb. Burpee Recommends: Handle bulbs carefully to avoid damage. Remove and destroy infested bulbs and plants as soon as you find them.

Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.

Spider mites: These tiny spider-like pests are about the size of a grain of pepper. They may be red, black, brown or yellow. They suck on the plant juices removing chlorophyll and injecting toxins which cause white dots on the foliage. There is often webbing visible on the plant. They cause the foliage to turn yellow and become dry and stippled. They multiply quickly and thrive in dry conditions. Burpee Recommends: Spider mites may be controlled with a forceful spray every other day. Try hot pepper wax or insecticidal soap. Check with your Cooperative Extension Service for miticide recommendations. 

Thrips: Thrips are tiny needle-thin insects that are black or straw colored. They suck the juices of plants and attack flower petals, leaves and stems. The plant will have a stippling, discolored flecking or silvering of the leaf surface. Thrips can spread many diseases from plant to plant. Burpee Recommends: Many thrips may be repelled by sheets of aluminum foil spread between rows of plants. Remove weeds from the bed and remove debris from the bed after frost. Check with your Cooperative Extension Service for pest controls. 


Iris FAQs

Why can’t I plant iris bulbs in the spring? Iris bulbs must be planted in the fall because they require a long period of cold temperatures in order to set their flower buds.

Can Iris be used as cut flowers? Yes, they make great cut flowers.

What do I do with my iris after blooming? Remove the spent bloom as soon as possible. Iris will benefit from an application of an organic fertilizer. Do not remove the leaves until they die down.

Why didn’t my iris bloom? There are several factors that will affect the blooms of iris including: Not enough of a cold period; too much nitrogen fertilizer as iris needs a low nitrogen fertilizer; diseases or insects.

Can I get the iris to bloom on an exact date? Unfortunately no, iris blooming time is effected by fluctuations in weather, precipitation, and temperature. These factors play essential roles in when and how well they bloom.

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