I would just put enough mulch on them to bring the soil up to ground level (Keep the mulch about 2" away from the canes where they emerge from the dirt).

Jackie

I would top up the holes with amended clay similar to what is in the holes. The roses won't mind the change of grade at all. If you leave the depressions, they could contribute to drainage problems during rainy periods.

Although your roses will be fine the way they are planted, modern horticulturalists do not recommend planting in deep, heavily amended holes. It is better to amend the whole planting area moderately to a depth of 10-12 inches. Any layers or sharp boundaries in the soil interfere with the movement of water and can lead to drainage problems or dry zones as well as the soil shrinkage you have observed.

If you know the pH of your alkaline clay, this would be a good opportunity to add the right amount of sulfur to eventually turn the soil slightly acid.

Yes, I have had the same experience, but I am gardening in glacier slurry, not pure clay. I have found that I truly like the uneven landscape because, to my eye, it is far more interesting that just the flat bed I originally planned.

I have planted spring bulbs in the areas that did not sink. Put in some stepping stones, so that I could plant other interesting ground covers and other plants. The neat part of this accident is that the companion plants are not competing with the roses for water or nutrients and the roses are performing very well.

I don't have a drainage problem because glacier slurry is quite porous, altho' one would not think that was possible while digging rose holes in the stuff. It's hard labor. If I had even tried to follow the advice of the modern horticulturist Michael mentioned above, I would have never gotten all of the roses planted.... 'o)

We get on average 30" of rain during the rainy season and there are no puddles, so I just make sure the mulch I put down doesn't touch the crown of the roses.

I ammend and feed the soil from the top because I never want to disturb the feeder roots of a rose, if I can help it. It's been interesting to see soil that seemed to be pure rock come alive and support a wide variety of plants.

I think I must be the odd gardener because I love the happy accidents ... they make me change my orignial plans and the garden is always evolving in a way that I had never "planned" into something that is far more interesting than I had ever imagined.

Smiles,
Lyn

Thanks for the information. The next holes that I dig for my expanding rose collection will certainly be less deep.

I realize that I forgot to mention that the roses in the sinking holes are healthy and appear quite happy. Perhaps I am making a problem about nothing. We also use compost as a mulch over the entire yard and plan to add more mulch/compost in a few weeks. So all roses will be getting another layer of mulch/compost. Depending on the age of the rose and the severity of the sinking, I will add more native soil or do nothing for now. It also depends on how much extra soil I have from preparing other areas of the yard for vegetables and annuals.

So far I have not seen drainage problems. We don't get a great deal of rain (14" a year) and water the yard with Netafim Techline CV, built in .6 gal an hour emitters spaced 18 inches apart.

Two months ago the PH of the rose holes was 7.2 before I added sulfur based on a formula calculating volume and the target PH . Yes, once again I made it more complex than necessary. I will checking the PH later this summer again.

When preparing your soil for planting roses, do you use a 50/50 soil and amendment ratio or something else?
Thanks for your advice,
Karen

I use around 1 part compost to 3 parts soil. The OM will mostly burn away in a few years, but decaying mulch will continue to modify the upper topsoil.

It will probably take more than a few months for the sulfur to have its full effect on pH. It depends on bacteria slowly oxidizing the sulfur.