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Contains current and previous editorials: Happy gardening in 2009.
Garden Diggings: An Introduction
Garden Diggings: Decoding Fertilizer (updated Spring 2009)
Garden Diggings: Look after your irises in the off-season
(updated Autumn 2009)
Garden Diggings: Iris borer control advice
(updated late 2007)
Garden Diggings: CIS Newsletter Sign-off

Photo: Iris reticulata, a harbinger of Spring and a new iris season. (photo by Chris Hollinshead)

Garden Diggings: An Introduction
Christopher Hollinshead

I look forward with pleasure to continuing to provide the CIS website as an iris resource for Canadian, American and International gardeners. I have served as a Director of the CIS since 1990 and produced the CIS Newsletter from 1994 until 2004. Recently I have served as the AIS RVP for Region 16 (Canada) from 2004 to 2007. And you may also already know me as the AIS website administrator, a position I have held since 2001.

My first involvement with irises stretches back to when I was 5 or 6 years old. My mother, Lois Hollinshead, grew irises at the side of our house. I used to help her garden and I remember that I was always in awe each year near the end of May and early June when the irises would put on a terrific show of bloom. They were all one color, blue flags as we sometimes called them. Many years later when I grew up and had my own house I brought some of those same irises from her garden and grew them in our garden. At that time I still had no idea that there existed anything but this one iris! That all changed one day when I visited a local Toronto spring garden show in 1989. One of the show booths involved irises and I stopped out of curiosity to talk. There I met a lady by the name of Verna Laurin, a member of the AIS and Canadian Iris Society (CIS). She informed me of the astounding news that there were thousands of different irises! I really liked the idea of that! Next stop was to join both the CIS and quite shortly after that the AIS. I have been an AIS member since about 1990. Subsequently I also served as the editor of the CIS Newsletter for 10 years from 1994 until 2004 and continue as the CIS website administrator from its initial inception in 1996 to date.

I live in Mississauga, Ontario, Canada and have gardened at this location since 1989. We have a fair sized suburban property and with lots of irises! I live there with my wife Marsha and we have 4 children, Kari, Scott, Shaun and Greg. Marsha is my USA connection as her home town is Port Huron, Michigan. Shaun is the one that has taken an interest in gardening and irises and has helped me since he could walk. He has his own iris patch and is quite proud of it. Additionally Shaun really wants to go to the Northwest USA with me and see one of those large and famous iris farms in that area.

As well as the normal functions of AIS RVP, one of my goals during my term as RVP from 2004-2007 was to promote the formation of local AIS/CIS affiliated local iris clubs and groups across Canada. These local clubs/societies/regions would be self-organizing stand alone entities all having a common bond of being affiliated with the AIS/CIS (i.e. their members would hopefully become AIS/CIS members). Each of these clubs/societies/regions would conduct their own activities, local iris sales, shows and other iris events, responsible only to themselves and as successful as their own initiatives. A formidable task perhaps but with e-mail and the internet as communication media it is quite a bit easier than in the past. On the Canadian Iris Society (CIS) website we have a Region 16 area to help provide information and activities details. You are welcome to stop by and visit.

And yes, I still grow the old blue flags. I like them very much; they are quite special to me. Happy digging in your garden. Enjoy your iris.

Christopher Hollinshead, 3070 Windwood Drive, Mississauga, ON L5N 2K3
phone: 905 567-8545 | e-mail: cdniris@gmail.com

Garden Diggings: Decoding Fertilizer (updated Spring 2009)

Did you ever wonder about the proliferation of fertilizers and the various formulations? This is for you. Applying the correct fertilizer at the correct time on the specific plant.

Yes, it can be confusing, there are dozens of products are out there. Fertilizers designed for different plants, different applications and even different times of the year on the same plants. Furthermore, fertilizers are labeled with various numbers such as 6-10-10. Overall it's about getting your soil in shape to grow the plants you desire. In most cases, the soil of a new prepared garden already contains what is needed to support your plants but over time your regularly used garden plot may need a nutritional boost.

The key is plant nutrition. Certain plants need more of some nutrients than others. Depending on the specific plant and whether the plant is currently developing new growth or is producing blooms/fruit their nutritional needs will vary over the seasonal life cycle. Those fertilizer labels/content codes are the key to matching such needs.

Macronutrients; The three main elements that plants need in large amounts are nitrogen (N), phosphorus (P) and potassium (K). The three numbers on your package label indicate the percentages of N, P and K in the mix, in that order. For example; a 6-10-10 fertilizer contains 6% nitrogen, 10% phosphorus, and 10% potassium.

A higher number means a higher concentration of that nutrient in the mix. The higher the number, the less you need to use. If you know the specific plant needs or how much of each nutrient your soil is lacking, you can buy the right fertilizer mixture to meet your requirements. There are several more macronutrients in the plant world but N, P, and K are the majors for most fertilizers. Each nutrient supports a particular aspect of your plant's growth and where you are in the season will predict which you want to supply in the greatest proportion.

  • Nitrogen (N) is the force behind healthy, abundant, green leaf growth. It's a key part of chlorophyll and basically boosts growth of the upper parts of a plant.

  • Phosphorus (P) boosts root, fruit and bloom growth.

  • Potassium (K) is also called "potash," and it builds the systemic health of the plant: strong cell walls that hold water and help nutrients move around inside the plant.

Plants need other types of nutrients in smaller amounts, including copper, iron, and zinc: these are referred to as the "micronutrients."

Kinds of fertilizer
Most garden centers offer supplies of organic and inorganic fertilizer as well as liquid, powdered, granular and timed-release delivery options.

Organic fertilizers are generally quite safe for your plants, they will not burn but it takes a longer time and a larger quantity to produce similar results in comparison with inorganic fertilizers. Alfalfa, well-composted manure, fish emulsion, seaweed, home compost, and "plant teas" are considered examples of organic fertilizer. Its important to note that while most inorganic fertilizers wash out of the soil over time, organic fertilizers are a permanent soil amendment that help your garden soil remain workable, aerated and able to better retain moisture/water.

Inorganic fertilizers are usually powerful and relatively quick to produce results and therefore require more careful application. They are highly concentrated and can sometimes provide nutrients at a greater level than your plant can handle. Adding inorganic fertilizers at higher than recommended concentrations can actually "burn" a plants' roots, cutting off growth where it starts. If you think you are seeing fertilizer burn, water heavily to reduce the concentration and wash chemicals away from the root zone. Some better quality inorganic fertilizers are provided with coated granules to release the plant nutrients at a slower rate in order to minimize the potential for "fertilizer burn". Used properly inorganic fertilizer can be quite effective. In large scale farming areas there is environmental concern about the impact of run-off from widespread use of inorganic fertilizers, "nitrogen pollution", that may boost algae growth in local water bodies and water tables. Home garden use of these products is not likely to have this kind of environmental impact.

Types of inorganic fertilizer: Granular: a fine gravel-like material that is applied on the surface or dug-in alongside a planting or mixed into your soil or potting medium before planting. Water soaking into the soil then releases the nutrients contained within the fertilizer granules.
Liquid: Usually in a concentrated form, designed to be mixed with water. Very quick release, the nutrients are absorbed by the roots along with the water.  Powdered: Dry and often crystalline-looking, these fertilizers are mixed with water and often used on seedlings, houseplants, and container gardens. Timed release: Products that react slowly with ambient water to release nutrients over weeks and months (check the package details). Most popular for house or container plants. Mix them in your soil when preparing your garden or container.

How much fertilizer to use and which one is best for irises?
In order to pick the correct fertilizer for your garden, it could be helpful to know what nutrients your soil may be missing and how much. A simple soil test, best done outside the growing season, can help you find out. Soil tests may be available in garden centers or through agricultural extension offices. Follow the provided directions, send in your sample and then receive a report back some time later.

Finally, what fertilizer mixture is recommended as best for irises? Review the following information from these noted commercial iris growers. Scientific research and years of experience provides this information specific to irises;

Schreiners Iris Gardens of Oregon recommends 6-10-10. They suggest to avoid using high nitrogen fertilizer as it can encourage rot problems.
Cooleys Iris Gardens of Oregon recommends springtime fertilizer of 8-37-11 and for the autumn 0-13-18 and the use of fertilizers low in nitrogen ratio to minimize risk of rot.
Chuck Chapman of Guelph, Ontario recommends to fertilize early in the growing season with 5-10-10 or 10-20-20 mixtures.

Specific fertilizer recommendations depend on your soil type but as a general guide, bone meal, superphosphate and 6-10-10 are all effective. A light application in the early spring and a second light application about a month after bloom will reward you with good growth and bloom. Container plants are fertilized more often than gardens because they have a higher plant mass to soil ratio. Use a fertilizer designed for containers if possible. The directions on the fertilizer label will tell you how much and how often to use.

General tips for fertilizing are as follows; Nutrient concentrations vary widely. Purchase the appropriate fertilizer mix for your specific use. Read the label and use the indicated amount. Use inorganic fertilizers lightly throughout the season: it's more effective and safer for your plants than heavy infrequent applications. Use organic fertilizers/compost to help amend the actual soil properties.

It's Springtime again and time to get digging in your garden, make those irises grow great this year. Get the garden tools ready...Happy Digging.

Chris Hollinshead
(updated Spring 2009)

Garden Diggings: Look after your irises in the off-season

Look after your irises in the off-season. There is an important item for iris specialist growers/gardeners to be aware of during the cool and wet autumn, winter and early spring. These are the conditions when the fungus Botrytis convoluta becomes active and problems can occur. Sometimes it is referred to as winter kill and then just written off as inevitable. It seems to affect new plantings of iris rhizomes more often than established clumps, invading the rhizome through a division cut on the rhizome or other rhizome damage. It is very disappointing to find in the springtime that you have lost the carefully chosen new iris acquisitions planted out the past July or August. So if you have ever had the unfortunate experience of a iris rhizome becoming well established and growing nicely into the late summer and autumn only the find it completely destroyed and covered with a gray-black powdery mould in the spring then you should read this with interest. On a couple of occasions in the past I had this experience, losing close to 80-100% of newly planted irises. You do not need accept this or just leave it to chance.


Botrytis convoluta is a cool weather pathogen, with active disease development occurring in the fall, winter and spring months. Fungus growth is checked in spring by rising soil temperatures and development of a suberization layer at the margin of the infected tissue. Botrytis convoluta remains inactive through the summer months. Apparently healthy rhizomes of iris cultivars may be infected with latent Botrytis convoluta infections during the summer that later become active during the autumn, winter and spring seasons and thus resulting in a destroyed iris rhizome in the springtime.


photo: cross-section of iris rhizome showing infected area of botrytis convoluta, note the presence of the gray-black botrytis fungus.


Botrytis symptoms:

Plant fails to grow in spring and a visual inspection reveals gray-black Botrytis convoluta fungus on iris rhizome and root system.

This fungus is known to thrive in a wide range of temperatures and climates but becomes most evident during the cool weather periods in early spring. At that time it appears as a dry, corky rot sometimes leaving the rhizome nearly weightless. It is usually accompanied by a mass of gray-black sclerotia on the rhizome or in the root mass. In most cases, at this point the complete plant is lost. A very discouraging outcome for a new and possibly expensive iris variety and additionally more so with the associated loss of a complete growing season and bloom enjoyment for that plant.


Occasionally, even though the main rhizome has been infected and destroyed, the small new rhizome increases will not be affected and they may be removed and replanted. Although better than losing the plant completely, this is again a discouraging setback as it will require at least another full growing season for the rescued small rhizome to reach bloom size maturity.  


Control of Botrytis:

An effective chemical control for this problem, previously available for 30+ years, Benlate (benomyl) is no longer available as it was discontinued by manufacturer Dupont in 2001. Currently, the use of the systemic fungicide Bayleton (triadimefon) from Bayer is a recommendation for the effective preventative control and curative treatment of Botrytis convoluta on irises. Triadimefon is the active ingredient found in Bayleton. Control of iris leaf spot is an additional side benefit associated with the use of this product. As usual please follow all instructions provided with the product.


There is product that is available in an easy to apply granular form, look for product that contains the active ingredient triadimefon. One of these is the Bayer Advanced product, Fungus Control for Lawns.


How it works: with data and information from Bayer Environmental Science - Bayleton is a triazole fungicide with systemic action that works from within the plant, so there is no risk of the fungicide being diluted or washed off. This systemic activity makes Bayleton an effective preventive and curative fungicide. Use Bayleton as part of a preventive fungicide program. Bayleton activity may extend for as long as 60 days, depending on environmental conditions.

(Note: some of these products mentioned may not be readily available in all areas due to local regulations)



A soil mulch for cold climates can be helpful to your irises. Mulching with soil about 5-7 cm (3 inches) can help prevent the rhizome damaging freezing/thawing cycles that can initiate problems of disease and rot. Important: Only cold climate areas should mulch and all of Canada and the northerly USA states would be considered to be in the category of a cold climate. Mulching in warmer climates (some of the more southerly USA states) is not needed and can promote other issues such as bacterial soft rot.


During the coldest months of the winter, it is a good idea to mulch your bearded irises with some means of protection against the severe cold weather and prevent heaving of the rhizomes. As the rhizome itself heaves above the soil line, the top of it can alternately freeze and thaw over and over during the early spring weather with typical warm days and freezing nights. This sometimes produces rhizome damage and may allow a higher incidence of subsequent rot and or botrytis infections.


A late season soil mulch could consist of 5-7 cm (3 inches) soil, loosely thrown over the rhizomes in very late fall and removing it again before the first warm days of spring. Pine needles or straw will work well but do not mulch with any material that will pack down when wet and hold moisture on the tops of the rhizomes. Use porous material that will admit air and is non water-retentive.

Keep in mind that depending on exactly where you live in Canada or USA, the winters may not be as early or as severe, so set your schedule accordingly. In Ontario, for example, we mulch from late November to mid-March.


Just as with the iris borer, remain vigilant in your garden during the so-called off seasons. Then reap the rewards of enjoying those superb irises performing at their best in your garden. Happy digging.  

Chris Hollinshead  
updated Autumn 2009

Garden Diggings: Iris borer control advice (updated late 2007)

The iris borer
Iris borer infestation can clearly be considered the main iris culture problem occurring in eastern North America. The iris borer (Macronoctua onusta) causes more damage to this popular plant than all of its other insect foes combined. It attacks practically all kinds of iris, from Tall Bearded through to and including the beardless types such as Japanese and Siberian. Although the borer damage to the plant starts earlier in the season it is most evident during July and August.

It is not always easy to tell where and when the borers are active. If the infestation is a particularly heavy one, entire plants may be killed or have a serious set back in growth. If the borer is already down within the rhizome, damage may not be readily evident above ground. Close inspection of the plant may be required. There are several ways in which one can tell that borers are present. A plant may have leaves that are loose and rotted at the base so that they can be easily pulled off. An exposed rhizome may show an entry hole that the borer has made in the top of the rhizome near the base of the leaf fan. The leaves of the new growth may be small and poorly developed. Some of the leaves may have badly eaten places along the edges.

The adult borer is a medium-sized, night-flying moth, quite inconspicuous with coloring that is mostly dark brown marked with black. In southern Ontario, the moths usually appear about the second or third week of September and depending on the weather, may continue through October and even into November. They mate and the females lay eggs that do not hatch until the following spring. The eggs are very small only about 1/50 of an inch across and less than half that in height. When first laid they are creamy-white but eventually they become distinctly lavender. The eggs are laid in groups or clusters and are carefully glued down. In studies, eggs have been found adhered to practically everything and anything that had a roughened surface-twigs, dead leaves, rusty nails, cloth, bits of wood, and wire screen. A single female may lay as many as 600 or 700 eggs in 24 hours and a total of more than 1400.

As previously stated, the eggs do not hatch until the following spring, usually about the end of April or the first week in May in the southern Ontario area. The newly hatched larvae are tiny, only about 1/16 of an inch in length. Almost at once they crawl up the iris plants and make small holes, like pinpricks, in the leaves. Then each larva gnaws out the soft tissue between the upper and the lower surface of the leaf, crawls inside and becomes a leafminer. From the small holes made in the foliage, droplets of sap exude. Later the larva bores down towards the base of the plant, chewing the edges of newly developing leaves. Finally, it gets to the rhizome where it makes tunnels. At this time the larva is about 1 1/2 inches long, has a reddish-brown head and a body that is distinctly pinkish. It eventually leaves the rhizome and goes into the soil to pupate. Chestnut-brown colored pupae may be found in the soil when digging iris for division, these should be destroyed and the surrounding iris rhizomes inspected for further borer larvae in earlier stages of development. Pupation in the soil lasts for about five weeks and the adult moths begin to hatch and appear about the middle of September.

Iris plants should be carefully watched during the summer months. If there is any evidence that borers are at work, the plants should be dug up, the borers removed and destroyed and the rhizomes carefully cleaned before being reset. It is not necessary to destroy the rhizomes, with the borer removed, most will recover well over the next growing season.

To control the iris borer a thorough clean up of the garden late in the fall and again early in the spring is most essential and helpful. Since egg clusters are found adhered to dead leaves and other debris, all possible garden debris should be removed and burned/disposed.

The controls are 3-fold... and you can use any combination or the ones that appeal:

1. Your iris bed should be extremely clean. No dead foliage should be allowed to linger... and both a fall total clean and a very early spring cleaning are imperative!
2. Inspect your plants carefully during the growing season. Watch for any telltale signs... notched leaves.... shiny appearance at the base of the fan... frass or sawdust. If you see anything like this... you can pinch the iris leaves and try to squash the larvae... or if it is later in the season you may need to go in with a knife and cut it out of your iris rhizome.
*3. Set up a spraying program with Cygon 2E. This systemic pesticide works effectively against the borer if it is applied 3 times proactively in the spring ... once at the first sign of iris growth , then 10 days later and a third time a further 10 days later. This should rid you of almost all of the iris borers but ...be vigilant! Invest in a commonly available garden sprayer unit for the application of the systemic product. A helpful tip is to add a couple of drops of liquid dishwashing soap to the Cygon 2E mixture. This makes the application easier as the soap breaks the surface tension on the iris leaves and the mixture sticks much more evenly/effectively.

In order to get an effective control on the situation you will have to do a couple of successive sprays of Cygon 2E in the springtime in order to interrupt the borer life cycle and reduce its population. If you miss just one or two they will still lay enough eggs in the autumn to cause you grief the next season! Fact is that you will miss some. So for this reason it is important to keep the controls going proactively each and every season.

*Footnote (late 2007): As Cygon 2E is now not made available for purchase any longer I have engaged in a research to find a replacement product that will enable effective control. Obviously the two manual methods are useful but perhaps not practical to those with large iris collections or limited time to engage in a season long process of continual manual inspection and control. Indeed I tried the manual control methodology for three years and the iris borer flourished and almost devastated my iris collection. At the end of the second year I determined that the manual methods were not working for me and that I needed a viable alternative control. I have obtained and used an extremely effective systemic control product in experimental trials with my iris over the past year and the initial results are excellent. More details to come on this at a later date as my research on this progresses into 2008. A Spring 2009 update to come.

Good luck and happy borer-free irising!

Chris Hollinshead  
Spring 2004 (updated late 2007)

Editorial CIS Newsletter: Autumn 2003/Winter 2004 

Dear iris/gardening friends;

Although our CIS Newsletter issues do not come out as quickly as the cover dates seem to roll around, we persevere and hope you enjoy your iris news. The Autumn 2003 CIS Newsletter issue will be my last one as CIS Newsletter Editor. I have produced the CIS Newsletter for almost ten years and during that time I have enjoyed bringing you information and news of your favorite flower. I will be continuing to produce the official CIS website which you are presently viewing.

This CIS Newsletter issue also contains the third and final installment of a series of 15 articles from iris friend and former AIS President Clarence Mahan. The articles provide background on the various AIS Award Medals. I’ve dubbed them “The Medal Chronicles”, enjoy reading them and learn. They are very informative, interesting and come from a well versed and informed authority.

One last time, happy irising to all of you.

Chris Hollinshead - Editor
utumn 2003/Winter 2004

If you wish to comment by e-mail, click here to contact Chris Hollinshead at: cdniris@gmail.com

* The CIS Newsletter is mailed to all current members of the Canadian Iris Society (CIS). For information on becoming a member please go to the Membership area of this website. A CIS membership form is available there.