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Plant Answer Line Question

Keywords: Perennials--Care and maintenance, Iris

Do I leave my Siberian iris alone through the winter, then cut them back in the spring when new growth starts to show, as I've done in the past, or do I cut them back now? My neighbor has had hers cut back for months now and insists her way is best...


According to the book The Siberian Iris, by Currier McEwen, 1996, you should "allow leaves to remain on the plants as long as they are green and adding energy to the plant through photosynthesis. When they turn brown in the fall, cut them off as low as possible and burn them.* It is risky to add them to the compost pile, as they may carry fungal spores, insect eggs, and other disease agents.

*Or put them in your trash (in a sealed bag).

Date 2018-05-04
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Plant Answer Line Question

Keywords: Perennials--Care and maintenance, Vegetative propagation, Iris

When is the best time to divide and transplant Irises? I have Japanese, bearded and yellow flag (I think) irises.


Rhizomatous irises (the kinds you have) are best divided in midsummer:

Lift rhizomatous kinds, such as bearded iris, in midsummer and cut rhizomes into sections, each with roots and a fan of leaves; replant, with tops barely covered, 6 inches apart. Flowers will be sparse the next year, but good thereafter.
(Source: American Horticultural Society Plant Propagation, ed. by A. Toogood, 1999, p. 202)

The optimum time..is six weeks after flowering. This is usually in midsummer, allowing time for the new rhizome to become established and make sufficient growth to produce fans to flower the following year. New roots that began growing immediately after flowering will then be strong enough to help anchor the new plants. Early spring is another suitable time, just as the other main period of root growth is about to start, but flowering may be forfeited, and if flowers are produced the stems will almost certainly need staking. Bearded iris cultivars are tough, and if the rhizome is large they can survive out of soil for many weeks. This is not an ideal situation, but it makes transport of the plants easy.
(Source: The Gardener's Guide to Growing Irises, by G. Stebbings, 1997, p. 93)

Good instructions can be found in these articles:
Digging, Dividing, and Replanting Bearded Irises
Garden Experiences: Dividing Bearded Iris

Date 2018-04-05
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Plant Answer Line Question

Keywords: Acorus, Thalia, Typha latifolia, Sagittaria latifolia, Pontederia cordata, Cornus alba, Cornus stolonifera, Spiraea douglasii, Athyrium filix-femina, Lysichiton americanus, Scrophularia, Wetland plants, Carex, Native plants--Care and maintenance, Slope stabilization and soil erosion, Iris, Deer

We need some advice and we are hoping you can help. We would like to replant the banks of our fish pond and want to know what kinds of plants would hold a steep slope and be compatible with the fish and each other. We have a large deer and elk population and we get substantial amounts of rain. We like grass-type shrubs and we need a ground cover that will not take over and is evergreen.


From the research I have done, it seems that a pond with a sloping side is a very good idea, but if erosion is a serious issue, you may want to think about both plants and physical controls such as coconut fiber matting to stabilize the banks. The Brooklyn Botanic Garden's guide (1997), The Natural Water Garden, has a description of using coconut fiber tubes (also called biologs) laid horizontally along a bank, which can also be used as a secure planting medium for seedlings.

As far as deer-resistant plants which may work for your site, iris and spiraea appear to be unappealing to deer, so you might want to try some of the irises which prefer moist situations, such as Iris laevigata, and Iris versicolor (blue flag), as well as Spiraea douglasii (hardhack).

Other plants which may help with preventing erosion are Lysichiton americanum (skunk cabbage), Athyrium filix-femina (lady fern), Carex obnupta (sedge), and Cornus stolonifera (red osier dogwood) or C. alba (red twig dogwood).

Some grassy or reedy plants which do well as marginal (water's edge) plants include Acorus calamus 'Variegatus' (variegated sweet flag), Pontederia cordata (pickerelweed), Sagittaria latifolia (American arrowhead), and Typha latifolia (cattail). All of these are deciduous.

For evergreen plants, you could try Scrophularia auriculata 'Variegata' (water figwort), an evergreen perennial with cream-edged foliage. The flowers should be deadheaded to prevent self-seeding. Thalia dealbata (hardy canna) is evergreen, with long-stalked blue-green leaves and violet flower spikes.

Date 2018-07-12
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Plant Answer Line Question

Keywords: Iris

I am looking for information on a Iris sibirica 'Mantra.' I want to know what it looks like, what its cultural requirements are etc. If you can find an image, that would be awesome.


The iris you mention is actually not a Siberian iris. Here is a photo from the Miller Garden website's alpine collection which lists this as a Pacific Coast iris, rather than Iris sibirica. This iris won an award of merit from the Pacific Coast Iris Society in 2000. Here is general cultural information from the King County Iris Society.

Pacific Coast Native Iris (PCN), or Californicae (CA), are much sought after in the Pacific Northwest as our climatic conditions are ideal for them. Their graceful and dainty flowers bloom April to June on stems 1' to 2' tall, in a wide variety of striking colors and patterns. These irises thrive in the marine coastal climate, with dry summers and cool, wet winters. Plants are very prolific and grow readily from seed. Transplanting, however, can be difficult. They are best moved or divided in the early fall, when root growth is active and can continue well into winter. Plants can also be moved prior to spring bloom.

Transplants must be kept well-watered until natural rainfall can maintain high soil moisture. They should be heavily mulched with bark dust, pine needles or leaves, to prevent frost damage to newly developing roots. Once established, plants are usually tolerant of normal freezes and periods of drought. If frost damage occurs to leaves, wait until well into spring to watch for signs of new growth. PCNs should receive at least a half a day of sunshine.

Date 2017-12-09
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Plant Answer Line Question

Keywords: Tulipa, Narcissus, Iris, Bulbs

This is my first year planting spring flowering bulbs, which grew nicely. I cut the dead flower and the stalk once it died back, and now the foliage is yellow. What am I supposed to do with the yellow foliage? Pull it out? Cut it off? Just leave it alone? Also, will planting some annual petunias now hurt the bulbs I have planted in the garden? How close can I plant the petunia to the bulbs? I was going to try and hide the yellow foliage.


The answer will depend on which bulbs you were growing. For example, daffodil stems should not be cut back until at least 6 weeks after the flowers have faded, and you should never tie the foliage in knots or braid it (this is a common but ill-advised habit). You can leave daffodils in the ground to naturalize and spread.

With tulips, you also need to wait at least 6 weeks from the fading of the flowers before cutting back the leaves.

With hyacinths, you can pull away dead foliage and flower stems as they fade. When the top growth has died down, you can either leave them in the ground or dig up the bulbs, dry them off, and store them for replanting.

If you are growing iris, you can cut the dead flower stems to the base, and cut away dead leaves in the summer. If they are bearded iris, the fan of leaves may be cut back in the fall to about 8 inches above the base.

(Source: The Plant Care Manual by Stefan Buczacki, Crown Publishers, 1993)

You can certainly plant your annual petunias quite close to bulbs like daffodils and tulips and other bulbous plants which are quite vertical. Just don't plant right on top of the bulbs. To disguise dying bulb foliage, use perennial ground cover plants that keep their leaves over the winter, and that have stems soft enough for bulbs to emerge through them. Hardy geraniums (true geraniums, also called cranesbill) and creeping veronica, such as Veronica peduncularis 'Georgia Blue,' are good choices. You can remove dried leaves as needed, and they can be tidied or groomed in early spring.

Date 2017-05-05
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Plant Answer Line Question

Keywords: Mulching, Iris

I covered my iris bed with wood chips to keep the ground from drying out so fast. Since the rhizomes grow partly above ground, will being covered with chips harm the plants?


Your mulch is unlikely to harm your bearded (rhizomatous) irises, as long as it is less than one inch thick over the rhizome tops and allows air through. Here is some information from The Gardener's Iris Book by William Shear: "How deep should the rhizome be set? That depends. In light-textured soils, it can be covered by as much as one inch of soil, but for average to heavier soils, the top of the rhizome is best left exposed to the healthful influences of sun and air. Remember that the rhizome is a stem, not a root, and needs to breathe!...If you do apply a mulch, it must be loose and airy, so it won't pack down and get soggy--a sure ticket to rotting rhizomes in the spring." Shear suggests pulling back the mulch in spring (since it is for freeze protection in his mind), but it seems to me that would defeat your purpose. You might meet both goals (moist soil and dry rhizome tops) by mulching around the irises but not right on them.

Date 2018-03-01
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Garden Tip

Keywords: Plant and garden societies, Vegetative propagation, Iris

August is a good time to lift and divide your Bearded Iris, but don't touch your Pacific Coast Native Iris until the rains return in fall. To learn more about the joys of growing this "Flower of the Rainbow" go to the American Iris Society's website.

The King County Iris Society holds lectures and events throughout the year and publishes a monthly newsletter. Their annual rhizome sale is September 13 and 14 at Crossroads Mall 15600 NE 8th St, Bellevue. To join the society send $10.00 to KCIS Membership Chair, PO Box 95538, Seattle, WA 98145-2538. Online at www.kcis.org.

Date: 2007-04-03
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May 31 2018 13:14:08