Winter Pastimes for Iris Enthusiasts

by Tom Waters

Thanksgiving week is upon us. Here in northern New Mexico, that means the garden is already put to bed for the winter. The first killing frost came late this year, near the end of October. But now everything is on hold, waiting for spring to bring it all back to life in March.

So what is a fanatical iris lover to do with all this time indoors? This is actually a welcome opportunity to catch up on various chores that get shunted aside during the growing season.

The first of my winter tasks is to update my garden maps. Garden maps are essential if you have more than just a handful of irises to keep track of. Many people use garden labels to identify their irises, but even if you do, a map is still essential. Labels can get pulled up, become illegible, or become damaged in all sorts of ways. Personally, I do not use labels with most of my irises; I find them unsightly and I strive for a more naturalistic look in my garden. So for me, a map is not just a backup, it is essential.

It is a good idea to make a map as accurate as possible. I have irregular shaped flower beds, and just sketching the shapes of the beds by eye can lead to bad distortions. So I actually measure to create the base map. It's a chore, but once done it does not need to be repeated often. As plants are removed, moved around, or added, it's simple enough to change the maps. I do this in the summer as I dig, replant, and add my new acquisitions. The result is a handful of papers - last year's maps with lots of pencil marks noting what has changed. Winter is the time to convert these scribbles into something more permanent.

I use Photoshop for my maps, but really any kind of drawing or graphics software would work fine. Why go to that trouble? Why not just use the original paper maps? The short answer is that computer files can be easily duplicated and backed up. If you've ever left a notebook outside and forgotten about it, you know the tragedy of irreplaceable records lost to weather damage. It's also all to easy for papers to get accidentally tossed or ruined, even when kept safe indoors.

Even if you don't want to use graphics software, it is a good practice to scan your hand-drawn maps and store them as computer files.

Winter is also the time to update whatever other records you keep on your irises. I keep track of the name and class of each iris I grow, where it is planted, when I obtained it and from whom, as well as hybridizer and year of introduction. There are specialized software applications specially designed to maintain records of garden plants, but I just use a regular spreadsheet. Almost everyone has Excel or a similar product on their computer, and keeping your records using a familiar standard product like this ensures that you will be able to maintain them even as the world of computers continues to change from year to year.

As a hybridizer, I also do some pedigree research over the winter. It's fun to trace the ancestry of the irises in your garden, and sometimes there are unexpected surprises in the family tree. The AIS Iris Encyclopedia is a good reference for doing this kind of ancestry research.

I also sometimes use the winter months to plan what I intend to discard or acquire in the coming year. Before the catalogs start coming in the spring, it is possible to impose a little discipline on oneself and make sensible decisions about how many new plants to bring into the garden. Of course, I never manage to adhere strictly to my plans, but setting some ground rules in the winter does help.

These winter chores actually provide some enjoyment for me. Maybe they are a kind of surrogate for being in the garden, as they draw my imagination into thoughts of next year's bloom.

The Autumn Iris Garden

by Tom Waters

Here in New Mexico, the autumn equinox has brought a chill to the air and a change in the light that says summer has gone. I thought I would write about a few aspects of iris gardening in the autumn.

Is it too late to plant bearded irises?

Allow at six weeks for newly planted irises
 to get established before the first frost

A good rule of thumb is that bearded irises should have at least six weeks to establish themselves before the first frost. Here, with average first frost around October 10, I certainly aim to have all my planting done by mid-September. Yet we've all been in situations where we get some unexpected irises at a sale or meeting or from friends late in the season, or just can't manage to get everything in the ground as soon as we'd like. The good news is that irises are pretty resilient, especially in areas where winters are not too severe. I've planted up to the first frost date without losing many. Things that just can't be planted should be potted up and placed in a sheltered spot to overwinter.


Should I trim back the leaves in autumn?

My leaves may look tired,
but please don't cut them!

Leaves and roots are both trimmed when digging and dividing irises, to reduce transpiration losses, to reduce demands on the already disturbed plant, and to make them more stable in the ground when replanted. Leaves should not be trimmed on established plants that you are not digging and dividing. I don't know how this practice got started, but it is not recommended. As long as leaves are green, they are photosynthesizing and producing food to strengthen the plant for winter. Trimming is not terribly damaging; the irises will survive it and still bloom next spring, but why set them back, even a little? I think some people like the tidy look of a neatly trimmed iris bed. (To be honest, autumn foliage can look pretty ragged and tired.) But I have enough to do in the garden just keeping up with chores that actually help the plants do better. I have no interest in doing a chore that makes them do worse, just for the sake of appearances or tidiness. An exception might be the foliage seems to be getting diseased, or if you are worried about possible rot or losses and want to get more light to the soil and air circulation around the fans. Mostly, though, such problems should be addressed by planting with proper spacing, and providing good summer care.


Should I fertilize?

A light top dressing of organic matter
helps feed the soil

Autumn and spring are when irises are in most rapid growth, so it is good to support them at this time of year with ample water and nutrients. As explained in an earlier blog post, there are good reasons to avoid synthetic fertilizers, especially if you have not had your soil tested and are not addressing a specific nutrient deficiency. I do apply a layer of partly composted mulch in the autumn (I usually try to do this a month or two before first frost), and sometimes also sprinkle on a blend of organic fertilizers. This encourages the soil life and improves soil structure. Since I also do this in spring, there is a more or less steady flow of decomposing organic matter into the soil. Autumn is a good time, because instead of drying out in the summer heat, the layer of organic matter will stay moist, and winter snows and temperature swings will help break it down.

If you are in a cold-winter climate where you use a heavy winter mulch to prevent heaving, it should not be applied now. Wait until the ground has frozen and winter is here to stay.

I collected seeds this summer. Should I plant them now?

Seeds from hand pollination and from
seed exchanges, ready for fall planting

Hybridizers grow irises from seeds (made mostly from planned cross-pollinations) to create new varieties, and sometimes hard-to-get iris species are available as seeds through seed exchanges. I plant my seeds around the time of first frost.This blog post covers all the basics of growing irises from seed. If you've never grown irises from seed before, it can be quite fun and interesting! A few words to the wise, however: named iris varieties do not come true from seed. Also, it takes about three years to get a blooming-sized iris from seed. So this is not an easy or inexpensive way to get more plants of your favorite irises. Division or purchasing additional rhizomes is the way to do that. Also, keep your seedlings separate from your named varieties. (If you plant seeds in the soil, that spot may be sprouting irises for a number of years. Do not plant named varieties there next year!) It creates trouble for future iris lovers if you get named varieties mixed up with unnamed seedlings, or circulate your seedlings among friends. Have fun, but be responsible with the plants you create.


Reblooming irises!

Historic reblooming iris
'Summer Whitewings' (G. P. Brown, 1960)

Some irises rebloom in the autumn after their normal spring bloom, and these can be a real joy at this time of year. September and October is the peak time for rebloom in most parts of North America. Different rebloomers are suited to different climates. If you want to start building your own collection to enjoy, check with the Reblooming Iris Society or with iris growers in your area. Rebloomers need water and nutrients during the summer and autumn, so do not slack off with your garden chores as the season wears on!

This is good advice for all your irises. It is tempting to "let things go" and fend for themselves as the days grow shorter (we all run out of steam at some point), but if you can give your irises the same level of care in autumn that you do in spring, they will thank you for it!

Winter Iris Gardening

by Tom Waters

This being the day after Christmas, it seemed appropriate to write something "seasonal" for this blog post. So what does winter mean for the iris grower?

A word to the wise: Iris growers live in many, many different climates. What is true in one climate may be false in another. Be suspicious of any gardening advice on such topics as winter care that is written as though it applies everywhere. In this post, I'll mention a few things that one might want to consider, but I do not offer any absolute advice. For that, you need to speak with other gardeners in your own area or just do some trial-and-error work on your own.

All irises grow in temperate climates. They are adapted to the changing seasons. Most kinds have periods of rapid growth in spring and autumn, but slow down or go dormant in summer and winter. In fact, irises need a distinct winter with cold temperatures in order to bloom; they will not do well in tropical climates.

Selecting irises for your winter conditions. All garden irises are ultimately derived from wild iris species from different parts of the northern hemisphere. The climate where those species live can tell you something about how those irises will do in various climates. Louisiana irises, for example, are native to the southeastern US, where winters are mild and summers are warm and wet.

Among the bearded irises, winter hardiness varies a great deal. The original diploid tall bearded irises come from the species Iris pallida and Iris variegata, native to central Europe, often at rather high altitudes. They have little difficulty surviving cold winters. These diploid types are today mostly found among the miniature tall bearded (MTB) irises. Modern tetraploid tall bearded irises also have species from the eastern Mediterranean in their ancestry, meaning that some of them fare poorly in colder climates. Depending on the particular mix of genes, modern TBs can be utterly hardy or quite tender, or anything in between. So how is one to know? Checking with other growers in your own area is always good advice, but one can also take a clue from the region where the iris was originally hybridized. Irises bred in Canada or in the US midwest are almost certain to be suited to cold winters, while those from the Pacific coast are not necessarily so. Border bearded irises (BBs) have the same ancestry as TBs, and so the same considerations apply.

Among the dwarf and median classes, miniature dwarfs (MDBs), standard dwarfs (SDBs), and intermediates (IBs) virtually all have Iris pumila in their ancestry. This tiny species is a native of central and eastern Europe, growing at higher elevations and in more continental climates than most of the TB species. It is very hardy, perhaps to a fault, because it has a reputation for failing to grow and bloom well in climates with mild winters. Consequently, growers in places like southern California and Arizona sometimes find that these types (the MDBs especially) do not do well for them.

Arilbreds vary in their degree of winter hardiness. The aril species grow in southwestern and central Asia. Although some of these are adapted to the very warm climate of the deserts of Israel, Jordan, and Syria, most arils are in fact mountain plants used to extreme winter cold and extreme summer heat. So why do northern growers find many arilbreds too tender for their climates? The fault is probably in their TB ancestry. The center of early arilbred breeding was Southern California, and the TBs used in arilbred breeding were those that did well in that mild-winter climate.

Having made these generalizations, I encourage iris growers to experiment with types that "conventional wisdom" might recommend against. Every garden has microclimates, and every category of irises has cultivars that are surprisingly adaptable.

Winter care: mulching. Irises are not very different in their needs from other perennials you may grow, so in climates where winter mulch is beneficial, it can be applied to iris plantings as well. The main purpose of a winter mulch is not to keep the plants warm, but to moderate the cycles of alternate freezing and thawing that can push plants out of the ground expose them to risk of winter rot. Snow makes an excellent insulator. If your climate is such that you can count on a fairly thick cover of snow all winter long, you have the ideal natural winter mulch!

I am not so fortunate here in northern New Mexico. We get temperatures below 0 degrees Fahrenheit every winter, most often without any snow cover at all. I do not apply a heavy much, but I do allow garden debris to stay in place over winter, giving the crowns of the plants some buffer against the wind and cold. I also put down a layer of cotton bur compost in the late autumn. Winter weather gradually degrades it and incorporates it into the soil, but in the meanwhile it seems to offer a little protection.

Beware that mulches can harbor overwintering insect pests and can collect water. In climates where these are issues of concern, it is best to forgo mulch.

Winter care: water. In climates where the ground freezes, watering in winter is nor desirable, and often not even possible, so winter offers relief from this particular garden duty. Many gardening books seem to assume this is true everywhere. However, if you live in a dry climate with spells of warm weather during the winter, you should pay attention and provide a little supplemental water as needed to keep the garden from becoming totally desiccated. Not much is needed: remember that the plants are dormant or semi-dormant, and that evaporation is less because of the cool temperatures.

Seeds! For those of us who like to grow irises from seeds, winter is an important time. Like most temperate perennials, irises have seeds that resist germination during the winter, to sprout when spring arrives. The cold and wet of winter are actually part of the preparation they need to germinate. The simplest way to grow irises from seeds is to plant them outdoors in the autumn, where they can overwinter and come up the following spring. Nature is unpredictable, of course, so many people prefer to use an indoor refrigeration process to replicate winter conditions. I'm not really set up for that kind of project, so I plant mine outdoors and let nature do her work.

Seeds from my own crosses get planted around the time of the first frost in autumn. Those I get from seed exchanges or other providers usually come later, in December or January. The longer they have to experience the winter wet and cold, the better. Since winter and spring weather here is erratic, germination is unpredictable. I generally leave the seeds in place for several years.

I hope I've touched on at least a few topics of interest. What are your own experiences of irises and winter?