Growing Organic Irises

INTRIGUING IRIS INFO

Growing irises is one of the most popular flowers to grow in the U.S. and worldwide.

There are over 300 varieties of Irises growing worldwide, varying in color from nearly blackish-purple to yellow and white.

Commercially, growing irises for their roots (orris root) is done for some perfumes and some brands of gin. The flowers are also used in aromatherapy and perfume.

The fleur-de-lis, a stylized iris, was the symbol of the House of Capet and became the French national symbol under Louis the Seventh; it is also the New Orleans Saints football team’s symbol.

Growing any of the 300+ varieties of irises may be grown in the same manner which will be outlined below.

WHEN TO PLANT IRISES

If you’ve purchased iris rhizomes (roots) at your local garden center, the best time to plant is in the late summer or early fall, to allow the roots time to get established before winter.

If you already have irises growing in your garden, harvest and divide the rhizomes every three to five years in the late summer or early fall and replant. This will give you lots more flowers over time.

You can plant iris rhizomes in pots in the springtime if you’re planning to keep them in the pots.

BEST PLANTING LOCATION FOR IRISES

Various species of irises have differing light requirements, so when you purchase your iris rhizomes, make sure you know where they’re going and get recommendations on varieties that do well in the location you plan to plant them in.

Bearded irises, for instance, flourish in full sun; they also do best with good air flow around the plants.

Siberian irises, on the other hand, do OK with light shade, but too much shade may diminish or eradicate flowers from blooming.

Irises, like most garden plants, like well-drained soil. If you dig a 12 inch by 12 inch hole and fill it with water, your soil should drain the water within 2 or 3 hours. If it doesn’t drain in that amount of time, you need to add compost or other organic matter to create better draining soil.

Well-drained soil is important for irises so that the rhizomes avoid root rot. Irises also prefer moist soil, so creating a balance that works is important.

If you live in regions that get very cold in the winters (below 14°F), you may want to provide a straw or leaf mulch to protect your plants.

PREPARING THE SOIL FOR PLANTING IRISES

Most irises prefer organically rich, light, loamy soil with a pH level between 5.5 and 7. If you need to raise the pH, add lime; to lower it, add sulfur.

Compost and/or well-composted manure will contain most, if not all, the needed nutrients for growing irises successfully. It will also help your soil drain better.

Loosen your soil to a depth of 10 to 12 inches, mixing in generous amounts of compost and/or composted manure where each rhizome will be planted, a couple weeks ahead of planting.

CHOOSING THE BEST VARIETIES FOR YOUR AREA

Check with your local garden stores or a good online or catalog retailer for information regarding the best varieties for your area. Northern climates will be different than warmer climates, and any knowledgeable garden center should have an expert in this topic.

Iris rhizomes are generally on hand at nurseries and garden stores in July and August, as well as mail order companies.

If your rhizomes are soft, have your supplier replace them as they’re susceptible to rot. This is rarely an issue with reputable rhizome suppliers. If there is an end that’s soft, it can also be cut off.

As always, our advice is to check with your county extension office to learn if there are any particular diseases that afflict irises in your region, then purchase varieties that are resistant to those diseases.

PLANTING IRISES IN CONTAINERS

If you want to plant irises in containers, use an all-purpose potting soil and at least a 12 inch diameter pot with at least one drainage hole in the bottom.

Unless you have an enormous container, it is inadvisable to plant more than one rhizome. If you do have a very large pot, space the rhizomes at least 6 inches apart.

Plant the rhizome with about a third of it sticking it out. If you’re going to put the container outside in a sunny area, you can bury it completely with ½ an inch of soil to prevent sunburn.

In 3 to 5 years you may need to divide the rhizomes in your container as they will get overcrowded. You can accomplish this by digging up the rhizome with a garden trowel and separating the root cluster into smaller bunches.

If any of the rhizome ends are soft or shriveled, cut those off, then plant the smaller rhizomes in new containers, your garden, or give them away to friends.

During the winter, if you live in a colder climate that sees temps below 14°F, you’ll want to move the containers to a protected area that stays above that temperature.

PLANTING IRIS RHIZOMES OR PLANTS OUTDOORS

You may either transplant rhizomes from containers or plant them when you purchase them from a garden center or reputable mail order company. You can also find iris seeds from some suppliers. I’ll talk about that in the next section.

As mentioned earlier, you can usually find iris root stock in late summer until the early fall. Make sure the rhizomes (roots) are firm and free from any visible damage.

When you are ready to plant, soak the roots overnight in water or a compost tea to prepare them for planting.

Loosen the soil about 10 inches deep, then make a hole about 4 inches deep. Ridge up the center of the hole and place the rhizome on the ridge, draping the roots over the sides of the ridge. Then fill the hole with dirt and pack it lightly around the rhizome.

Plant the rhizomes about ½ inch below the surface of the soil and water well. If your soil is clayey, leave the top of the rhizome slightly exposed. You can go deeper in well-drained soils.

Space your plants 12 to 18 inches apart. I recommend planting at least 3 varieties alternating for some very nice color variety in your garden.

You can plant irises closer together without any harm if you want to have a lot of flowers more quickly in an area. However, you may have to divide rhizomes sooner if you do this.

If you purchased a potted iris at a garden center, trim the leaves to about 6 inches in height to allow the roots to establish themselves; leave the plant and roots at the same level as they were in the pot.

Water your plants or rhizomes well after planting.

GROWING IRISES FROM SEED

Some people prefer to start irises from seed. Iris seeds are readily available from many of the catalog seed companies.

You can start iris seeds in the spring to give them a good start…you won’t see blooms the first year, but you should the second.

You can also plant the seeds in the late fall or early winter, although they may not come up until spring.

If you want to go the seed route, the first thing you’ll want to do is soak your seeds from 2 day to 2 weeks. Change the water daily (hint: use a strainer or you’ll lose the seeds down the drain). Soaking iris seeds will plump them up and help them sprout once planted.

If you’re planting them in soil blocks or peat pots, plant 2 or 3 seeds per pot, then thin them to the best plant once they’re about 2 inches tall.

Plant the seeds about ½ an inch deep and ½ an inch apart, whether indoor in pots or outdoors in your garden.

When you transplant your plants to the garden when they’re a couple inches tall, just follow the instructions in the section above. You’ll see blooms the following year.

DIRECTLY SOWING IRIS SEEDS IN YOUR GARDEN

Follow the same basic instructions above, but thin the plants continually after they reach a couple inches in height until the plants are about 12 inches apart.

DIVIDING IRIS RHIZOMES

As Irises reach an age of about 3 to 5 years, depending on how close together you’ve planted them, you may notice a decrease in blooms. This may signal that the rhizomes (roots) are getting overcrowded and it’s time to divide your rhizomes.

If you look down around the bases of your plants and the rhizomes are being pushed out of the ground by other rhizomes, it’s definitely time to dig up your plants and divide the roots.

A few weeks after blooming, usually July or August, cut back your plant’s leaves to 3 or 4 inches tall. Dig up the roots and cut them into 3 or 4 inch sections. Each section should have a set of leaves on it.

Re-plant the rhizomes per the instructions a few sections above, 12 to 18 inches apart. You should now have a lot more plants or maybe some happy neighbors if you pass the extra roots on.

GROWING BEAUTIFUL IRISES

Irises will grow and bloom in the springtime without much help and if you’ve followed our instructions above, your irises will be the envy of the neighborhood.

After the bloom is over, it’s a good idea to trim the flower stalks to a couple inches tall to keep them from going to seed. The reason for this is to prevent seedlings from sapping the nutrients out of the soil.

A couple weeks after the bloom is over, remove the outer leaves that are browning. If you see any leaf spots, trim those leaves off as well.

To prepare your growing irises to bloom beautifully next year, cut back the tops of the plants to about 6 inches in the fall and clean up the debris.

If you’re in an area that has temps that fall below 14°F in the fall, you may want to mulch your irises with straw or chopped leaves – just make sure the wind won’t blow them away!

In the spring it’s a good idea to spread a thin layer (an inch or so) of compost over the ground around your plants…this will give them a nutrient boost and create yet another gorgeous bloom.

The one fertilizer we are recommending for every plant in your garden, including irises, is a brand new product we tested last year called Organic Garden Miracle™. This past gardening season we tested this liquid organic leaf spray fertilizer in our gardens. We sprayed fruits, veggies, flowers, and herbs every couple weeks and they were more robust than the unsprayed plants. We’re impressed.

MULCHING AND WEEDING

Unlike other garden plants, mulching isn’t a good idea for irises in the spring or summer as it can cause root rot.

As discussed earlier, mulching is a good idea in the winter if you’re in a cold climate area like we are in NE Washington State. We saw the mercury drop well below zero this past winter several times. However, remove the mulch as soon as hard freezing danger is past.

Because mulching is not recommended for spring and summer, it’s a good idea to remove weeds from competing with your irises. Hand-pulling is really the only option as you don’t want to be cutting the roots which are very close to or above the ground surface.

WATERING IRISES

Growing irises require somewhat frequent but short bouts of watering due to the shallowness of their root systems.

Depending on the time of spring or summer, you may be able to water as little as one time per week but as often as 4 times weekly during hot spells. Obviously if it’s rainy, you won’t need to water at all at times.

After the bloom, it’s best not to water much at all as it may cause root rot. This rule will change if you have a re-blooming iris variety that blooms in the fall. Check with your seed company for the correct instructions on those varieties.

All in all with irises, it’s easier to overwater than underwater, so check with your county extension to find what is recommended for your area and the variety of iris that you’re growing.

COMPANION PLANTING AND ROTATION CONSIDERATIONS

When considering what grows best with irises, you really probably should decide what flowers look best with irises.

However, there are some plants and flowers that both look good and grow well in similar conditions, particularly the Forsythia flower.

The purple coneflower also grows well in similar soil conditions and is long-stemmed and is complementary to irises in cut flower arrangements.

One plant that grows well with irises is the Creeping Myrtle, or Vinca Minor. It is an evergreen ground cover that has shiny leaves. It also shades the rhizomes from the sun.

Another attractive ground cover is known as Lamb’s Ear. It has greenish-gray leaves that have a bit of a wooly texture. They grow to about 12 inches in height and attractively hide the cut-back irises after bloom is done.

Other flowers that deserve honorable mentions are Echinacea, Geraniums, Peonies, Columbine, Narcissus, Lilies, and so many others that it would take a lot of typing to mention them, so you’ll just have to be creative and discuss flora and fauna with other flower people!

STORING RHIZOMES

We discussed digging up your rhizomes above and re-planting, but you can also store them for later usage.

If you harvest the rhizomes, dust them with a sulfur dust to prevent insects from bothering them, then bury them in a container filled with peat moss.

Keep the container in a refrigerator or other cool area until you’re ready to plant them…they can keep this way for several months.

PREVENTATIVE AND NATURAL SOLUTIONS TO COMMON PESTS

The most common pest to afflict irises is aptly name the Iris Borer. The iris borer larvae assault the central leaf stalk and burrow into the rhizome.

The iris borer larvae is a pink caterpillar that has rows of black spots on its sides and these pests are the most damaging to irises of all iris pests.

Once they’re in the rhizome, these caterpillars pupate and emerge as a large brown moth with black markings.

You’ll know your irises are being attacked if you see stains on the leaves and chewed leaf edges in the springtime, and later rotting holes in the rhizomes.

To prevent this pest from proliferating, make sure to remove any dead leaves or other plant rubbish in the fall. This will remove the eggs that the moths lay.

Hand-picking the caterpillars in the spring can be effective. Diatomaceous Earth is also effective in ridding plants of caterpillars. It shreds the inside of caterpillars when they ingest the dust, but you do have to reapply after a rain or watering as it loses its effectiveness when damp.
Aphids will occasionally infest irises. These small green, gray, pink, or black insects suck the juices out of your iris leaves, and they can transmit the iris mosaic to your flowers.
Diatomaceous Earth is effective against aphids as well, as well as insecticidal soap sprays.
Occasional infestation of aphids can be controlled by spraying off with the hose or using an insecticidal soap.
The yellowish-green wormy-looking Verbena Bud Moth larvae will burrow into new iris buds and shoots. They’re about a half an inch long.
If you find infected buds, cut them off and destroy them. Removing faded flowers also will discourage the moths from laying eggs.
Tiny Iris Thrips, both the milk-white larvae and the black-bodied adults, puncture the surfaces of young iris leaves, then suck the plant juices from the perforations.
An infestation of these tiny bugs (about 1/20th of an inch long) can damage the flower buds and weaken the plants.
Insecticidal soap sprays and diatomaceous earth are effective against thrips as well. Predatory mites are also available commercially.
ENVIRONMENTAL FACTORS
Poor flowering can be caused by a number of things including the rhizomes being planted too deep, the plants being in too shady an area, or even too much nitrogen (not usually a problem with organic gardens).
It can also happen if the rhizomes become to crowded, as discussed at length above.
Bacterial Soft Rot may occur if there are breaks or wounds in the rhizome. Too much moisture, fresh manure, or too much nitrogen can cause this rot which will kill the plant.
Cleaning up dead material and making sure you plant your irises in well-drained soil with good sunlight will usually prevent this disease.

If a plant is infected, dig it up and destroy it, or cut out the parts of the rhizome that are infected, then lay out the other pieces in the sun to dry.

Fungus rots, such as Sclerotic Rot or Southern Blight, are often problems in warm, humid areas. These fungi will usually be on or just below the surface and will appear as brownish-yellow seed-like growths.

Another fungus, the Botrytis Rhizome Rot, occurs in cooler area and appears as blackish seed-like growths on the rhizomes and leaf bases.

These fungi will cause the leaf bases and rhizomes to develop a dry, pithy, grayish-colored rot.

Lots of sunlight, breathing room, and well-drained soil are the best prevention for fungal diseases. Also, cleaning up dead rubbish from your iris bed will help immensely in preventing fungal rot.

If plants do become infected, cut out the rotted areas from the rhizome and dry them in the sun and remove and destroy all infected leaves.

Iris Leaf Spots can disfigure plants and leaves and deteriorate the health of your iris plants. These spots show up just about the same time as the plants flower.

These spots are yellowish at first, then turn gray in their centers with black fruiting tufts. The fungus will overwinter in plant debris.

As with previous diseases, giving your plants lots of space, sunlight, and well-drained soil will usually prevent this disease. Keep your flowerbed free of decaying plant rubbish and you’ll likely never see this problem.

Rust and Bacterial Leaf Spot: Rust causes small, raised, darkish-red spots on the leaves of irises, whereas Bacterial Leaf Spot creates darkish-green, watery streaks and spots that become yellow later, then translucent.

As with the previous environmental ailments, breathing room, lots of sunshine, and loose, well-draining soil will prevent most problems such as these. Keeping your flowerbed clean in the fall is also key to reducing disease.

Root-knot Nematodes and Lesion Nematodes are microscopic

Root-knot nematodes and lesion nematodes are minute worms that are a bane of gardeners, and yes, they do infect irises as well.

They create knots, or galls on plant roots that appear as beads on a string and will cause the rhizomes to rot off completely.

Again, as with the previous diseases, lots of space, lots of sunlight, and well-drained soil will prevent nematodes. And keeping your flowerbed clean in the fall.

However, one difference is that if an area is infected, you should get rid of all the plants and rhizomes in that area and leave the area fallow for a year or two.

Finally, the Iris Mosaic is spread to Irises by aphids. The mosaic will cause the flowers to be striped or mottled, and the leaves to have light green streaks.

To prevent the mosaic, controlling aphids is important as outlined in the previous section. If the mosaic does infect your plants, the only way to get rid of it is to dig up and destroy damaged plants or it will infect your entire iris patch.

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