I dug up an iris bed today and then started to prepare it to be replanted. When I've prepared beds in the past I dug the soil eleven inches down, soaking it where it was too hard to dig. Today my soil is loose for the top six inches, but, again, I will have to soak the soil to be able to dig those last five inches. It occurred to me (because it is hot and I am getting older) that maybe six inches is enough.

How far down do you all dig when you are preparing an iris bed? I am interested in hearing your thoughts and opinions. Thanks.

I suppose, the type of soil would dictate how deeply it needs to be tilled . In the beds I have amended, the soil is "fluffy"....almost TOO loose, so all I do is scratch deep enough to get the roots in the ground. If you are spading in 'amendments", you would probably want to get them mixed into the top 8"of soil, anyway

Through over 30 years of adding mulch to my garden the soil is less clay than it originally was. I'm not going to dig up my entire gardens, filled with assorted perennials, in order to further amend the soil. So I just take my lady shovel and dig a very small hole- just large enough to bury the roots, and let the rhizome be close to the soil surface. The iris do great. In early spring and a month after blooming I may sprinkle some low- nitrogen fertilizer around them. Generally they thrive. We don't water except during very prolonged periods of drought. So don't talk me of re-bloomers. After the death of Daughter of Stars, I realized my style of gardening is not likely to accommodate them. Nor do I wish to make a separate bed just for them, and have to water it weekly. That's just not for me.

Andrea, I don't think I dig any deeper than 6", but I have soil very similar to Arlyn and don't amend my soil.

Arlyn, Scott, and Daisy,

Thanks for your answers. My soil is fairly heavy clay and unless it is amended with compost it becomes pretty much like concrete if not watered. I am leaning towards just digging down six inches, even though the AIS advises cultivating to a depth of 10 inches.

Daisy, I totally agree with you about rebloomers. I'm happy just to get one bloom a year!

I think 6" would be more than plenty.

Andrea, I hear you on the 'hot' and 'older'! I have very heavy clay soil and what I did last year (because drought and record setting heatwave ) when I needed to get a lot of things in the (rock hard) ground fast, was to loosen the soil 5-6 inches down and then add 3-4 inches of mulch/good garden soil on top of that. It was faster and easier than double digging in baked clay soil, even though it meant I had to push a wheelbarrow around. Whatever solution you choose I wish you good luck and you have my sympathy. It's hard work!

Lilli, Loosening the soil 5-6 inches down and then adding a few inches of amendments
sounds like a brilliant solution.

I was digging up irises planted in my raised beds which contain ten inches of excellent soil and even their roots were mostly about six inches long. Some were longer, but most were not. My observation was the roots seemed to fan out more than go deep.

Andrea, the roots may grow, to accommodate, the surrounding soil & moisture conditions.
For instance, if you had planted a rhizome in a deep pot, with continuity of all soil within, some may grow deeper roots. While low moisture levels & poor soil, may tend to lead to roots being located near the surface.
If you only dig a small area, to begin with, if soil is poor, then the "increases" may be affected, later. If soil is "too loose" then falling over ( or blown by wind) , of stalk, may more easily occur.

A continuous soil of similar consistency deeply dug, may allow some Tall Bearded, to attain full size, allow for better drainage, good nutrient uptake, moisture retention & just general overall better growth, in the future.
While I used to "forbid' anyone to walk upon the flower beds, which tends to rather easily compact soils, that had been dug to change the structure & loosen it, to be begin with, to help avoid compaction & reduces drainage , aereation, etc..

For example, till your soil, amend for one square foot & deep also, , Then take one "step" on it, & then water that area, then see & watch what happens... That doesn't mean, one should avoid firming soil around rhizome, when planting, or watering it , often enough, to get it well established.

Good points, Shawn.

Considering that the iris roots hanging down from the rhizome never seem to be longer than about 3" long when I receive them from growers, or dig them up myself, I think that the AIS recommendation to cultivating to 10" is probably needless overkill.

Also, any experienced farmer will say that you don't till when the soil is wet or soaked, because that creates a lot of hard clumps, particularly if you are trying to dig up hard-pan clay. I think it's best just to till down to the hard-pan, and add amendments to what you have managed to till. Our topsoil in this area of Maryland is only about 4" deep, if that, before we hit the impossibly hard hardpan clay. When making my gardens for the first time, I ran a Rototiller over the area 3 times and could not penetrate the hardpan. My garden has done fine, nevertheless. If I need a deeper hole than 3", a combination of shovel, or even a 6' iron prybar can be brought to the task!

I have to agree with Shawn that how deep the roots grow, depends a lot on culture. In the redwood root infested areas, which are mostly clay soil, with automatic sprinkling 2x/week, I was lucky to get roots 3" deep. In 8-10" deep pots with saucers (to hold any drip), saucers filled with half/half mix of planting mix and fine redwood mulch, and 2x/week watering, I usually got roots going down to the bottom of the pots, and sometimes out the bottom or circling around.

Exactly, Poly. Everyone is growing their Iris differently & in a variety of conditions, yet, maybe some are doing it fairly similarly.
I've received Iris rhizomes, that had their roots- -trimmed- -to about four inches in length...
Had they not been cut, they most likely would, or could have been much longer. Simply giving a brief spray with the hose, occasionally , is going to cause that Iris to grow roots, mainly near the surface, simply because of using the same repeated, watering technique.

If your summer is a "dry" one, or you do not receive adequate, deep, frequently regular precipitation then you may expect the same. If you do not water adequately, deeply enough, & often enough, to get those deeply grown roots, you are unlikely to ever get them to grow in that fashion, as Poly gave you an example of, above. Just like. when planted in a deep pot, watered regularly, in a good soil mix, & watered deeply.

Unless, your garden soil has inadequate & poor drainage entirely, it may not be such a good idea, or your precipitation in summer , is rather to the extreme. Or worse yet, a combination of both...

I've had a rather great variety of plants, through a variety of mail order sources, purchased at garden centers, big box stores, - you name it ! This has been over many years time, & some vendors had extremely different growing techniques. Some, varied, form my own. But, while you tend to be 'thinking" the roots may only stay near the surface & treat it that way, that is about exactly the results that you are going get.
While deeply watering, in deeply amended, well draining soil may give an entirely different results.

So, I will pose this question. Why else then, would some people go to such great lengths, to get such a deeply, "properly, well dug" & amended bed , for Tall Bearded Iris ?

Interesting to hear how long the roots grow for you all. I guess my experience here on the sandy soil is a lot different from those growing on hard, compact soils. Roots can get very long here in a dry summer. In 2018, which was record dry, several were over 2 feet long. To connect to what Shawn said above, this was on areas that received deep irrigation maybe every 10-14 days.

In contrast, all roots were pathetic in the record wet summer of 2017.

In a normal year I still expect the roots to grow a feet deep and spread even more.

This year I see some differences between the ones growing in the newer sand beds and the ones standing in the more heavily amended kitchen garden. It is hardly surprising, but clearly the lighter the soil, the more roots.

Yes, William. Now you've noticed a difference ! Like I mentioned above..Unless, your garden soil has entirely poor drainage, or "your precipitation in summer, is rather to the extreme.''.
My meaning ,of precipitation ," rather to the extreme" is just that, which is well above average. Which, as in William's case that is exactly what happened , in 2017, "in the record wet summer."

Deep & regular irrigation, leads to longer deeper roots. Like I tried to explain, compared to treating them, as though they are shallow rooted & watering accordingly, because that's what you will tend to see them appear to grow like & gives you an appearance, which causes you to think, that is just exactly how they grow , which is almost a direct result of those planting & watering, methods, including low precipitation.

I would much prefer sandy soil, than to heavy clay. This has been a rather very dry summer here , yet in years where rainfall can be frequent, with heavy summer downpours, then it is much different & some people specifically bring in top soil, to make raised beds, simply because of that. Using a raised bed, still improves drainage & while also can help prevent root rot, which may lead to the rhizome itself, to begin rotting. Lacking that,or ability to deeply dig a bed, & having hard dry soil in summer, can be "worked around" by preparing ahead of time, when soil is moist & workable & amending, well in advance, or building a "raised bed.".. (Unless, it is a drought, year around.)

Most of all, you want to avoid compaction of nearby soil, by simply walking on it repeatedly as that tends to lead to heavy, dense soil, & after any decent amount of precipitation, which then in turn, causes it to becomes soggy or possibly even muddy, & that compaction, reduces aereation of the soil, which would have otherwise, helped to avoid root rot. Or, the precipitation, may simply become "run off", instead of helping it to be absorbed more deeply. Whereas, if it is deeply dug, amended & friable, then should more readily absorb water more deeply, while still avoiding lack of oxygenation.

Wow! I never know that iris roots could grow so long! I guess with my hardpan clay soil, they will just have to spread out some sideways, and make do. We do not have a sprinkler system to irrigate. Nevertheless, they seem to do well here.

Here's my clump of Beverly Sills this Spring, for example:



They do adapt.

Yes Daisy. Plants can & do adapt to some conditions & some plants are more "forgiving", about the conditions than others, under which they're grown...

I had one plant, which grows a long "tap root" & I just couldn't quite figure out, what was going on with it, as it kept failing to flower for several years, each spring.
Well, I was slightly "poking around" in the nearby soil & suddenly realized the tap root had grown sideways, amazingly just a few inches under the soil, almost three feet, from the "crown" ! haha
It just simply refused to grow downward, into a small area of "hardpan" soil, upon which it had been sown & found it much "easier" to grow sideways, than it ever could try, to grow straight down.

You've probably been amending your soil, for some years, adequately enough, to keep that Iris , in rather fairly good health. If you avoid chemicals, earthworms have a beneficial effect, too.

I have no exact way of proving it, but the deep long roots, may be a way, for the Iris, to survive some prolonged periods of drought.
While shallow roots, may be another way, of adapting to the environment, by collecting precipitation, that is reduced , or overall, in lesser total annual amounts. Including from dew at night.

As long as the rhizome itself, does not become dessicated while nearly dormant in summer, it can grow new roots, but then I wouldn't expect it to increase as well either , when it does so.

Or , as it otherwise might, to recover from drought, in poor soils & low moisture conditions, unless it does produce roots located near the surface to adapt to the situation. I've seen the Iris rhizomes before, where they were actually nearly growing completely, at the very surface of the soil & still bloom away, during spring.