Saturday, November 9, 2013

Geraniums Aflame in November...

Geranium fremontii at Cherokee Ranch, late October 2013
It's constructive to compare the first two pictures: it's hard to believe these are very comparably sized, and that each would look so much like the other--despite their growing 60 miles apart! Typical Geranium fremontii, by the way, is a much rangier plant that has been lumped with the very different G. caespitosum by Botanists who should know better: I'll leave that for another blog...

Geranium fremontii in South Park, eary July 2011
There is no question that geranium in bloom are lovely and well deserving their ensconced place in our gardens as groundcovers and summer wonders. But November is the month when their foliage finally catches fire--I always am amazed how green most stay through September and October, but by the time hard frost hits hard, they get the hint and turn....magnificently!

Geranium dalmaticum
This miniature is popular with rock gardeners, but should be better known: Plant Select is aiming to do that by promoting this next spring as part of the Petites program. I have hyperlinked both programs--you should familiarize yourself with them: I have worked almost a quarter century as part of the team that has made these a wonderful way of promoting deserving new and underutilized plants...the geranium will pop up early next year on the Petites page--check back then!

Geranium dalmaticum closeup
The leaves end up being quite red, although earlier in the fall there's much yellow in evidence.

Geranium pretense at DBG
A rambunctious weed--but such a beautiful one! I've admired this in Europe and wild high on the Altai Mountains of Central Asia--and have removed hundreds of unwanted seedlings from my rock gardens. But never altogether!
Geranium regelii at my garden
 This has been lumped with pretense, and does indeed look like a miniature form. But my clones are different in their fall color as well as size...

Geranium renardii at DBG this week
Geranium renardii closeup
 When you consider how rather homely the palish flowers on Renard's geranium really are, I wonder why I am so fond of it...this clump has persisted for over 30 years in the same spot--one of relatively few plants that have made it so long at Denver Botanic Gardens.

Geranium x cantabrigense
This is not one of the "standard" clones--this is a seedling that occurred spontaneously at Stonecrop in New York and shared with the Gardens. It is also easily 30 years old or more. The pink flowers are lovely enough--but the fall foliage is almost showier..

Geranium magniflorum
Jim Archibald and I collected this at the base of Joubert's pass in the East Cape--although I have seen it growing abundantly at the highest elevations throughout Lesotho. It has possibly been confused with the utterly different Geranium magnificum and not made the impact that it should: it is a stunning garden plant and unlike any other geranium I grow its foliage actually PERSISTS ALL WINTER--i.e. it's a true evergreen. And it looks like very lustrous, very finely cut parsley...isn't that reason enough to grow a plant?
Geranium sanguineum closeup at DBG
And finally, the "bloody geranium" itself: the hot magenta or pink flowers hardly justify the Latin and common names, but the fall foliage more than justifies the sanguine epithet!

November on my horticultural calendar is brightly colored by the Callery pears all over Denver, by the Oaks and the coloring of geraniums in all the gardens I love...and in nature of course (that biggest Garden of them all!)


  1. Hi Panayoti, This has been gnawing at me for a while now. Looking at your photos reminds me of how rock gardeners always say that rock and gravel should be added to “improve drainage.” The simple fact is adding rock or gravel alone does not improve drainage. There are many rocky and gravelly areas were water pools. Just think about all the beautiful alpine ponds you’ve seen.
    The best way to improve drainage is by having slope. If a gardener does not have the appropriate slope then their best option is usually a raised bed. At this point, rock gardeners should be thinking “But my dry land plants grow better in a gritty or rocky medium?” This is not due to drainage, which might actually be faster if the rocks were not taking up pore space. This is due to changes in the soil water holding capacity.
    Soil with a large volume of rock and/or gravel holds less moisture. Soil that holds less moisture will dry faster once the sun beings evaporating off water.
    I categorize my potting mixtures by pH and how quickly the sun will dry them after I water or they receive rain. I do not make my mediums more or less filled with grit/gravel to improve drainage. I do it to change the water holding capacity so I can alter how quickly they dry.


  2. You are opening big cans of contention--although I think you're basically right (I have a few plant friends who would LOVE nothing more than to debate this with you)...truth be said, I use gravel on my rock gardens on the surface to keep down weeds (which it does pretty well), and I know it keeps the volume of the soil much cooler below by reflectring heat and essentially shading the soil are reflecting sunlight. Alpines seem to almost demand it, just as they sulk and often die with leaf mulch.

  3. Panayoti, I tried growing the Aethionema seed you sent me in pure grit. They grew. However, some of the seeds were catapulted by rain into nearby flats containing some potting soil mixed in with the grit. The plants that grew in the flats with some potting soil grew much better. I have not grown many European alpines. I've mainly concentrated on North American species. All the plants I have grown appear to grow better with some potting soil in the medium. My transplanting survival rate increased dramatically after I added some potting soil to my soil mix. I believe a very few plants might find the molds in leaf mulch to be pathogenic. I have never personally observed any problem with leaf mulch from my oaks and maples. I have had a problem mulching with grass clippings. The mold that grows on grass clippings seems to impact hemerocallis leaves. I have noticed that pure young leaf mould supports a larger than typical population of worms, slugs, and pillbugs. This increase in population likely increases herbivory on plants. The experts tell us soil for lawns should have 5% organic matter. I usually add about 20% potting mix, by volume, to my grit when growing alpines. I expect aged leaf mould would work almost as well as potting mix in most cases. A few plants might need peat moss, instead of leaf mould. I just do not see how providing no organic component could be beneficial to plants. Alpine areas are cold. Organic material breaks down slowly in the cold. I would think alpine soils would have a higher proportion of organic material than comparable soils at a lower elevation.


  4. Panayoti, I also wanted to comment on the assertion that “I use gravel on my rock gardens on the surface to keep down weeds (which it does pretty well), and I know it keeps the volume of the soil much cooler below by reflectring heat and essentially shading the soil are reflecting sunlight.”
    If you actually measure the temperature of the soil with a thermometer you will find that soil mulched with gravel gets much hotter than regular potting mix. The reason the potting mix stays cooler is because of its high capillary action. Potting mix is designed to wick water to the surface where it cools the soil by evaporation. In contrast, soils mulched with gravel get very hot. This might be a benefit if you live in a cool climate and are trying to grow plants from a warmer location. In my area, the heat from gravel mulch in full sun would be death to most high alpines. This is why I put my pots with alpines under a tree where they receive shade during the middle of the day.
    I should mention that leaf mulch can cause problems for plants as the temperature rises. Leaf mulch does not have a high capillary action like potting soil. Leaf mulch does not conduct away heat as well as gravel. The brown color of leaf mulch absorbs a lot of the sun’s rays. The high rate of gain and low rate of loss makes leaves get very hot in the summer sun. A mulch of leaves can get so hot that it often burns any plant tissue touching the mulch. I prevent this problem by removing leaf mulch in spring. The leaf mulch protects the plants from cold all winter. What has not decomposed by spring gets raked away and put in the compost pile. I do not do this for my alpines since cold hardiness is generally not a problem for them in my area. Also, many are evergreen and likely prefer some sun throughout the winter. My leave mulch is used for my herbaceous species, like temperate orchids, or to insulate plants that need protection in my climate, like Mimulus cardinalis.

  5. You have obviously done a lot of thinking about the soil and gravel issues, James--which I certainly respect! Remember, however, that we live in very different worlds (until you have gardened on the high, windy, harsh Plains of Colorado as I have for 55 years, and killed several tens of thousands of taxa) I wouldn't get too categorical: the one profound, lasting lesson I have learned in 34 years of public horticulture is that I certainly don't know half as much as I used to! I appreciate your zeal, but remember we're supposed to be talking Geraniums: I get several hundred visitors and they may wonder what all this fuss and bother is about: you must do your own blog about soil and gravel: believe you me, I shall be sure to comment!


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