Rock Gardening in The Midwest - Problems?

Submitted by Peter George on

Over the past few months I've made a point of asking various friends across the US and Canada about particular problems they may have growing rock garden plants in their particular locale. As a function of elevation, precipitation, humidity, etc. many have given up on growing various alpines but have found more than adequate choices to populate their gardens, which provide them with beauty, persistence and an acceptable level of challenge. But some have persisted in their view that THEIR area of the US simply doesn't allow for growing so many of our favorites, and restricts them to (please pardon me if you are a Hosta lover) hostas, and the various woodland plants such as trillium. In particular, the Midwest has more than a few gardeners who find their climate utterly inhospitable to most rock garden plants. So, if you are a gardener in Illinois, Missouri, Ohio, Kansas, Oklahoma, Iowa, or even Arkansas, can you offer some insights into what you grow and how you manage to overcome the hot and muggy summers and the unreliable (or totally non-existent) snow-cover? Thanks in advance


Submitted by Lori S. on Sun, 01/08/2012 - 13:40

As participation on the NARGS forum has gradually increased, perhaps it's time to bring this thread to the fore again.
Since the original query was posed, there have been some interesting observations on how dryland alpines can be grown successfully in what would seem to be some very inhospitable climates for them:

Has anyone applied these or other practical and sustainable methods successfully in the area in question?

I have no experience growing in the area mentioned, but coming from a generally much colder area, and one in which the norm is unreliable snow cover (here in the chinook belt east of the Rockies), my feeling has always been that the value/"necessity" of snow cover is greatly overestimated, and that plant hardiness is often underestimated, and further, that plant death that might be attributed to "lack of snow cover" may often be related instead to poor drainage/standing water/"winter wet".  Comments?  Thoughts?  

(That ought to generate some talk!  ;) )

Submitted by RickR on Mon, 01/09/2012 - 22:05

Does ground that is covered with snow drain better, or is it that the bulk of the water is tied up in the snow and there is relatively little liquid water to drain?

Submitted by Hoy on Thu, 01/12/2012 - 14:38

Well, my experience is that much depends on whether the soil under the snowcover is frozen or not or whether the snow melts or sublimate in spring. The latter is normal with much sun in spring. Although it is freezing temperatures the snow can disappear without melting. I've experienced it several times, even on Svalbard.

Submitted by Anonymous (not verified) on Thu, 01/12/2012 - 20:06

I would like to add that snow cover insulates the ground helping prevent it from freezing.  Water does not move through frozen ground well.  This is observed often in Spring.  When the ground is frozen and rain occurs, everything is a muddy mess.  The water just puddles on the surface.  Once the frozen earth has thawed, precipitation again percolates through the soil allowing it to dry.  I have even observed this phenomena at my parent's house.  They live on a level section a top an old gravel moraine.  During the Spring thaw their yard is often a lake.  After the thaw has occurred it is extremely dry.


Submitted by ClifflineGardens on Fri, 05/03/2013 - 08:50

I'm trying to grow Alpines in Chicago. I'm growing in window boxes on the third floor window sills. Theyre dropping like flies after only two 80F days. There's reflection off the windows, but they've got generous organic matter and two inches of quartzite chips. I'm wondering if I need to redo my soil mix. I used three even parts sand, perlite, peat. Could there be too much moisture held in this mix? The plants get afternoon shade. Note where it says DEAD! After reading, I should have expected the Calceolaria to die, but I think the others should have been fine.

My current windowsill is planted with;
Acantholimon armenum
Androsace hirtella - DEAD
Anemone blanda 'enem' - DEAD
Arabis x kellereri
Astragalus angustifolius - DEAD
Calceolaria ex. garden Barrie Porteous - DEAD
Campanula betulifolia
Campanula trogerae x betufoliae
Daphne 'Lawrence Crocker'
Daphe 'Schlyteri' - DEAD
Draba bryoides
Penstemon uintahensis
Penstemon virens
Petrophyton hendersonii - DEAD
Saxifraga 'Sieberi'
Silene acaulis 'Anne Spiegel'

Submitted by Lori S. on Fri, 05/03/2013 - 15:38

Are you certain they suddenly "up and died" in two days, and that they were not actually already dead after the winter?

Edit:  What I meant is, was there new growth or flowers on them, that were clearly killed in the warm weather?  (If that was the case, it would be clear with Anemone blanda, which would have spent the winter as a dormant corm.)

Other thoughts.... I used to have some troughs up on tufa blocks and it seemed as though plants had a tougher time surviving the winter in them, presumably due to a bit less insulation as they were not in contact with the ground.  Your troughs look as though they are reasonably large but given that they are not in contact with the ground, and are 3 stories up, exposed to wind, the conditions may be quite a bit harsher than at ground level.
Some of your plants may just be harder to grow than others.  For example, I find some Androsace very easy to grow here (the stoloniferous types, e.g. Androsace sempervivoides) but have trouble with the tight, hummocky ones like Androsace hirtella.
And then, the other thing is that it can just take time, experimentation, and, in my case, I'd say just plain dumb luck, to figure out what grows well in your conditions and what doesn't.

Submitted by RickR on Fri, 05/03/2013 - 15:46

The thought also crossed my mind.  Most notably with evergreens, often winter injury doesn't show up until roots can't meet the demand that evapotranspiration exerts.  But this also makes me wonder about the tolerance for heat in the early spring verses summer.  

Before this week, we had two non-consecutive days with a high in the 50sF, and no 60s before we were slammed with four days in the 70s.  This Corydalis solida grows in a small area on the south side of my dark brown house.  Yes, it heats up fast.  I went to work in the morning and there were a couple flowers that had opened.  When I came home, all flowers had blossomed and were already visible wilty.


Submitted by ClifflineGardens on Sun, 05/05/2013 - 08:56

Well, the soil mix I made does drain rapidly. So maybe it was the winter weather that killed them. We had an awful drought in Chicago last summer, but I watered. These went in in the Fall and grew for about three weeks before winter hit. So I wouldn't really have called them established.

Submitted by Gene Mirro on Sun, 05/05/2013 - 09:13

Rapid freezing and thawing of the roots will kill even cold-hardy plants.  It's not the temperature that gets them, but the rate of change of temperature.  There are a few things you can do to reduce the rate of change:
1.  Increase the thermal mass of the planting by using a bigger container and filling it with more mix.
2.  Insulate the container somehow. Maybe use a foam cooler as a container.  Or glue some insulating foam onto the outside of your container.
3.  Make sure the mix is very moist.  Maybe use a more water-retentive mix.  Water stores a lot of heat, and takes a lot longer to freeze and thaw than dry mix.
4.  Mulch.
5.  Protect from wind.

None of these things will change the temperature that the mix ultimately reaches.  They will just slow the rate of change.

Submitted by Gene Mirro on Mon, 05/06/2013 - 11:02

You say "the plants get afternoon shade".  So that means they are facing east, right?  In the winter, the plants and soil will be frozen at night, and then will be quickly defrosted by the morning sun.  That's deadly.  It's better to place them in a west-facing location, so that they have all morning to thaw out before the sun hits them.  Better yet, don't let the sun hit them at all in the winter.  They aren't growing anyway.

Submitted by ClifflineGardens on Mon, 05/06/2013 - 13:56

I have problems with squirrels digging and pulling plants out, window sills are the only safe place.

Eastern exposures killing roots through rapid freeze thaw...I never considered that. My 15 sq ft of garden is precious, there's not much room for failure.

Here's my update, as of 10.18.2013 


Survivors - Acantholimon armenum, Arabis x kellereri, Campanula betulifolia, Daphne 'Lawrence Crocker', Penstemon uintahensis

Species which were propagated this summer and proved to survive the Chicago 4th floor in 90% equal parts sand, diatomite, perlite and 10% peat;

Aquilegia caerulea, Aquilegia jonesii, Aquilegia canadensis, Penstemon digitalis, P. hirsutus, P. grandiflorus, Helianthus occidentalis, Houstonia longifolia, Delosperma nubigenum, Sempervivums, Solidago sciaphila, Aster macrophyllus, Aster laevis, Koeleria glauca, Eragrostis spectabilis, Opuntia humifusa, Sedums (duh), Petrorhagia saxifraga, Phemeranthus calycinus, Phemeranthus rugospermum, Viola palmata, Allium sikkimense, Viola adunca, Silene regia, Antennaria neglecta, Scutellaria leonardii, Arenaria stricta


It is of note, that on the 4th floor, it seems that everything becomes rather choice, and small. All species of Aquilegia are the same size. Jonesii is quite small, conversely, A. canadensis can be three feet. On my sills, they're maybe 4 inches tall. 


Submitted by RickR on Fri, 10/18/2013 - 21:25

Thanks for the useful information, GreenRoofer.  I've never seen Phemeranthus rugospermum before.  It is just as nice (or nicer) as the Phemeranthus parviflorus in western Minnesota.  The two species are nearly identical, botanically speaking.  I hope you didn't let the seeds drop to the sidewalk below!

Phemeranthus parviflorus


Gathered all I could, I am hoping that the seeds crossed with the Phemeranthus calycinus to make something new. There's some overlap in their blooming times, but I'm not sure if this genus is 'promiscuous'.


Gathered all I could, I am hoping that the seeds crossed with the Phemeranthus calycinus to make something new. There's some overlap in their blooming times, but I'm not sure if this genus is 'promiscuous'.



I can only say that I have had two species of Phemeranthus, calycinus (to 8 inches) and an unidentified species kinda like brevifolia (to 4 inches), that hop around in my pot menagerie for at least five years.  I have never observed any intermediaries.

It will be interesting to see how the plants do over winter.. Have the pots been insulated at all? I find a few plants here will survive in small pots sitting out on top of the soil, but very few. Any plants I have outside in pots are sunk into the soil for winter.. There is some point where the pot becomes large enough sitting on the soil for plants to survive, but I'm not sure where the line is...

Grouped should help give them some soil mass to keep temps more consistent. I'd probably try to insulate in some way as well, but my climate is more severe than yours- even pots sitting on the surface of the ground, under snow most of the winter, with no freeze thaw, are not safe- but of course we have the freeze/thaw in spring and fall..

Looking forward to your spring update.