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!

Growing Irises from Seed

by Tom Waters

We usually propagate irises by division: digging up a large clump, breaking apart the individual rhizomes, and replanting. This method is easy, and because most irises increase rapidly, within a few years you will have plenty of them. This post is about a different way of propagating irises: planting seeds. This is a process that has some challenges, but also has some wonderful rewards. If you've never thought about growing irises from seeds, or have wondered about it but are unsure how to start, read on!

Why?

If you are hybridizing, you will necessarily be growing irises from seed. Hybridizing refers to cross-pollinating irises to produce new varieties. When you cross two different irises, the result is a pod of seeds. Each of the seedlings will grow into a new individual, not exactly like any other iris. Propagating by division only creates exact copies of the original plant, whereas progagation from seed creates only brand new plants, different from either parent. Even if you are not intending to embark on serious hybridizing program to create new varieties to sell commercially, making crosses and raising seedlings can be fun and interesting.

Woohoo! Iris seeds just arrived from Czechia

But hybridizing is not the only reason you might want to raise irises from seed. Some types of irises may just not be obtainable from commercial growers as plants, but you may be able to acquire seeds from a collector or from a seed exchange. This is especially true of iris species, the wild irises from different parts of the world. It can be very difficult to import live plants from other countries, but importing seeds is usually much easier. I've gotten seeds of iris species from collectors in the Czech Republic and from seed exchanges run by the Species Iris Group of North America (SIGNA), the British Iris Society (BIS), the Scottish Rock Garden Club (SRGC), and the North American Rock Garden Society (NARGS). Although the seedlings from a given offering of species seeds will all be different, in subtle or obvious ways, they will all still be plants of that named species, unless the person providing the seed misidentified the plant, or unless it was accidentally cross-pollinated by a different species growing nearby.

Growing irises from seeds also has some other advantages: you get a wide variety of different plants, so you can choose the ones that do best in your climate or whose appearance you prefer. Growing from seed is also a way to eliminate virus infection, should that be a problem.

Finally, growing irises (or any plant) from seeds is a very satisfying experience. It connects you with the whole process of growth, from its very beginning. There's nothing quite like seeing the first bloom of a plant you've grown from seed yourself.

How?

The process of growing irises from seeds is not (usually) very difficult, but it does require patience and attention to factors that you might not have considered if your only experience of raising plants from seeds is growing vegetables or annuals. There have been many articles written on special ways to grow iris seeds; you can find a number of them on the web. In this post, I am not going to suggest one particular method as superior, but just give you an overview of the basics, so that you can get started and learn what works for you.

There are two requirements for germinating iris seeds:

1. They must experience several months of cold temperatures, followed by a warming period.

2. They must have adequate moisture.

Seeds planted into pots sunk in the ground
 (gravel on top protects from washout
and animal interferenece)

The simplest way to meet these two requirements is to plant the seeds outdoors in the autumn or early winter, and let nature take its course--assisting with supplemental water if natural precipitation is insufficient. Seeds can be planted straight in the soil, or in pots sunk into the ground or just left on a porch or in a cold frame. A planting depth of 1 cm or 1/2 inch is suitable for most seeds. Germination usually occurs around the time of iris bloom in the spring.

Some growers prefer to give the seeds their cold treatment ("stratification") indoors, by putting the seeds in baggies with slightly moist vermiculite, perlite, or other sterile medium and refrigerating them for 60 days or more. The advantage of indoor stratification is greater control over the conditions, and the possibility of getting germination a few months earlier. The disadvantage is that you need to be prepared to grow on the seedlings indoors under grow lights for some time, until they are ready to be hardened off and planted outdoors.

Newly sprouted seedlings!

I prefer the outdoor method, as it is less bother and easier to manage with large numbers of seedlings. If I had an extra refrigerator to use for seeds, I might prefer indoor germination.

Whatever method is used to germinate the seeds, they should be transplanted to a semi-permanent seedling bed outdoors when they have at least three leaves. Some may bloom a year later. The year after that, most should bloom and you can decide which ones to keep and which to discard.

The reason the period of cold temperature is needed is that irises, like many perennials from temperate climates, cannot easily survive a winter while still small seedlings. When germination occurs in the spring, rather than in the fall, the young plants have the best possible chance of survival. In contrast, most annuals are fast-growing, opportunistic plants that can grow, flower, and produce seed whenever there is a few months of warm weather.

Dormancy

Even if the requirements above are met, not all the seeds will sprout the first year. With garden variety bearded irises, the percentage will usually be more than 50%, and can approach 100%. Most of the remainder will sprout the following year. At the other extreme, aril irises may sprout a few at a time over a period of 10 years or more. Why is this? It is nature's "insurance policy" against calamities and harsh conditions of various sorts. If all seeds sprouted at the same time, a drought, flood, fire, or other disaster could destroy the whole population. By having the seeds sprout over the course of several years, it is virtually guaranteed that some will survive.

For the gardener, however, such protracted dormancy is a frustration. Few of us want to wait a decade for the seeds we plant to sprout! In irises, dormancy has at least two causes: the hardness of the seed coat, which makes it mechanically difficult for the seedling to emerge, and chemical germination inhibitors inside the seed itself. In nature, the action of water and the cycles of freezing and thawing serve to gradually weaken the seed coat and to leach away the chemical inhibitors.

Some growers have success by planting seed fresh, before it has a chance to dry out. For some types, at least, this can bypass dormancy and result in immediate germination. Of course, one then needs a way to care for the seedlings over winter.

A variety of techniques are used to overcome dormancy artificially. One can attempt to leach out the germination inhibitors by prolonged soaking or use of running water. One can overcome the hard seedcoat by abrasion or chipping (cutting away the seedcoat to expose the embryo). This "forced germination" procedure is often recommended for difficult oncocyclus seeds. The ultimate procedure is to excise the embryo under sterile conditions, and germinate it on a nutrient agar medium. This "embryo culture" can be used to germinate seeds that will not germinate any other way, but it is very demanding work and the young seedlings are very vulnerable.

Whether you choose to use any of these techniques for overcoming dormancy will depend on whether the basic method is giving adequate germination for the types of seeds you grow. I think the best advice is to try natural germination first, and then move on to progressively more invasive and difficult techniques if you need to.

The Payoff

I encourage everyone to trying growing irises from seeds at least once, whether it's making a cross or two in your own garden or ordering a packet of seeds from a seed exchange. It's an adventure, and the first bloom of an iris you've raised from seed yourself makes it all worth the wait!

Here are three seedlings from the same cross, arilbred 'Aztec Prince' (Tasco, 2009) X Iris pumila:

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?

PCI Seed Germination Tricks

Kathleen Sayce

It's the wintery time of year in the northern hemisphere, when gardeners think about the coming growing season, and when iris seeds are distributed from seed exchanges. When PCI seeds are fresh, plant them immediately, and within weeks seedlings will appear. But who has fresh seeds? To send seeds to a seed exchange, they must be thoroughly dry, or they will mold in the seed packets. Alert readers will recall that I wrote about this last fall. Once PCI seeds are dry, they may have to be coaxed into germination. If those seeds are more than three years old, the coaxing might have to be pretty thorough.

PCI 'Mission Santa Cruz' is an older variety, and one I return to again and again for new seedlings.  The plants are sturdy in the coastal Pacific Northwest climate, and flower color is dark and near-red. Unfortunately, in 2014 I did not get any seed from this plant. 

Some general seed starting tips:

First, PCI seeds don't like 'warm' conditions for germination. 'Warm' when compared to many cultivated perennials is 60 F and above––in a cool to warm greenhouse, for example. PCI seeds germinate best between 40-55 F; the actual temperature varies with the species. Tenax and innominata like cooler temperatures, munzii definitely prefers the warmer end. Most hybrids germinate towards the warmer end of the range, around 50 F, though it's always better to stay on the cool side with any PCI seed lot for which the genetic source is unknown.

Second, if the seeds are truly fresh, and were not completely dried, then plant them immediately in well drained potting soil. Soak the pot with several waterings, put them somewhere bright and cool, and stand back. They will be up within weeks.

Third, if the seeds are old, particularly more than three years old, it may help to presoak them in fresh water. Presoaking can be in a dish of water, a small plastic bag, or in a mesh bag hung in the water tank of your toilet. Keeping the seeds at 40-50 F while presoaking may also help; my soaking seeds are kept in an unheated shop that stays between 40-55 degrees all winter.


Fourth, scarify them, removing some of the seed coat by gently rubbing the seeds between two sheets of fine sandpaper or scrubbing them gently in a food mill. 

A food mill is a great tool to rough up seed coats. Put the seeds in, rotate the handle 10-20 times, and shake out the bits of seed coat that were scraped off. 

I've tried one, two, three, up to thirty days of soaking, and also hung mesh bags of seeds in the water tank of the toilet. By weighing the seeds day by day as they soaked, I tracked the uptake of water, watched the seed coat loosen, and in some cases, saw the radicle (the proto-root) emerge.

Yes, those are emerging proto-roots and shoots on PC Iris seeds. They were scarified and soaked in water, and burst out of their seed coats, ready to grow. 

I wrote about these methods for the SPCNI Almanac in Spring 2012, if you would like to read about the details of my tests. [This winter the SPCNI web manager will post back issues of the Almanac and Pacific Iris on the SPCNI website (www.pacificcoastiris.org ); past years' issues will be available to the public, including the first 40 years of the Almanac.]

Here's a new method to try––one I plan to test next year: Soak seeds in cold tea. [I decaffeinate tea at home by steeping loose tea leaves in boiling water, use a French coffee press (or a sieve), time the steep for 45 seconds, pour off the water (save it for seed soaking), add fresh hot water to steep for the cup of tea to drink.] When soaking Iris seeds, change the cold (not hot!) tea every day. For some kinds of irises, this acidic, tannin-rich water seems to help remove germination inhibitors. And it allows you to enjoy teas even when you can not tolerate caffeine––which happened to me last year very abruptly after a lifetime of drinking fully-loaded black teas.

Choices for potting PCI seeds are wide. Any container that can hold potting soil and drain off water will work. I've migrated to large rectangular styrofoam boxes (AKA fish boxes) over the past few years. I punch holes in the bottom, fill with a 1:1 mix of coarse pumice and potting soil, put the seeds on the top in rows, add labels, and a covering of chicken grit (usually granite). Then the planters go outside for the year––and no matter what the weather, they stay outside. I put them on the east side of my house where they get rain, wind, snow, a half day of sun, a rain of conifer needles, the occasional tree branch, and are close to a hose bib for summer watering. The seeds and subsequent seedlings spend a year in this container. This way, they have cool deep root runs, and are fine for their second winter. They are planted out the second spring, about 15 months after planting.

Styrofoam boxes have drain holes; there's a layer of chicken grit (in this case a reddish granite) over the top, and then wire mesh to keep the squirrels and jays from the seedlings––both of these 'varmints' like to eat sprouting Iris seeds. 

I practiced fall planting of seedlings for years, until I lost ninety percent of them a couple of years running to mid fall snow and freezing weather. Now I wait for early spring, and plant out sturdy year old plants instead.

Waiting for spring:  the next crop of PC Iris seedlings are ready to plant. Sturdy, healthy, they will be fine for the rest of winter in these styrofoam boxes, with 9-inch deep root runs and good drainage. 

My methods for seed germination are in place for the new year, including a test of a new method. What are you planning to do?