It seems that the fields of landscaping and gardening are
full of many timeworn statements that people like to repeat over and over. Some
of these green “rules of thumb” are tried and true, while others may
not be so true.
One landscape stereotype regarding tree growth rates that is being challenged is the old adage that “oak trees grow slowly”. I have heard and read this many times and I have repeated this mantra myself for years. But a study of urban trees in the Denver Metro area, published by the Colorado State Forest Service, got me to rethink that stereotype.
This tree study recorded the growth rates of 19 commonly
planted trees planted in public land in the Denver suburb of Westminster, for
24 years. The authors of the study measured the trunk diameters of the trees in
1992, 2000, 2008, and 2016.
The most eye-opening nugget of information in this report is
that the white oak group of trees (bur, swamp white and English oak) were the
3rd fastest growing trees in the study! They grew faster than green ash,
lindens or honeylocust trees. They even
had the same rate of recorded growth as silver maples, a species often referred
to as a “fast grower.”
Data table from the Colorado State Forest Service’s study “Growth Rates of Common Urban Trees in Westminster, Colorado”. Authors: K.A. Wood and A.M. Poulson
One important take-away from this study for me is the fact
that we should reevaluate what trees seem to be the best for planting in
challenging ecosystems such as the urban/suburban areas of the high plains
where Denver sits. It is worth quoting the State Forest Service report to
emphasize this point:
“Some tree species revealed to be fast or moderate growers in this
study have previously been viewed as slow growers, and they are often passed
over at planting time. However, equating growth rates with vigor can be
misleading, as some of the slower-growing tree types on this list can be the
most adaptable to the area (including hawthorn, hackberry and honeylocust).
Adding newly discovered fast-growing species to the planting palette and
incorporating hardy, slow-growing species will maximize the success of planting
projects and promote species diversity.”
To be clear, it is only one type of oak trees (white oaks)
that exhibited fast growth in the study sample. Red oak was also in the study
and showed slower growth. The authors note this is possibly due to the low pH
of high plains soils.
It very well could be that other types of oak trees grow
slowly too, but we don’t have data for that. Or, perhaps another study may come
along and challenge that, as well.
So, as with many “rule-of-thumb” type
statements, don’t believe it until you have seen some data to back it up.
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It’s summer, which means in Colorado and other surrounding states in the Central Plains/Inter-mountain West region of the country, it is Hail Season!
Earlier in the Summer, the Denver area had several sessions of hail that ripped through gardens and landscapes late one June night. Avid gardens who’d been awakened by the cacophony of thunder, torrential rain and hail that night, sleepily rushed out in the morning to find shredded plants and debris scattered everywhere. I myself had many plants I’d been babying from seed and roots all Spring which were severely torn up by the barrage of hail stones.
This horticultural carnage got me wondering what plants are best at surviving the annual severe weather in our region? As I walked around the yard sadly inspecting the damage, it was easy to see that the native and climate adapted plants fared best from the aerial ice-bullet onslaught. So I thought it might be a good idea to create a list of “hail-proof” (or at least “hail-resistant”) plants. The following list of plants is just a cursory look at some possible plant choices that should be better able to handle hail storms:
Ornamental Grasses:
-Many, many varieties. Some of the hardiest, and easiest to grow in our region are Feather Reed (Calamagrostis spp.), Switch grass (Panicum virgatum), Little Bluestem (Schizachyrium scoparium), and Giant Sacaton (Sporobolus wrightii)
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This past August, the Denver area was captivated by another blooming of a corpse flower (Amorphophallus titanum) at the Denver Botanic Gardens. Large crowds lined up to get their chance to get a whiff of the bloom that emits a fragrance similar to a rotting animal carcass. I was one of the masses of plant geeks who waited in line early on a Friday morning before work, just to get a glimpse and a sniff of the malodorous corpse flower. The first bloom of an Amorphophallus titanum plant doesn’t appear until after 8-20 years of vegetative growth. A second bloom from a corpse flower may not occur until as long as 10 years after the previous bloom. Although this was the Denver Botanic Gardens third bloom of a corpse flower, the rare occurrence for a bloom (along with the plant’s other odd characteristics) leads to a lot of excitement for botanical enthusiasts.
Amorphophallus titanum photographed at the Denver Botanic Gardens on August 31, 2018.
The foul stench of the bloom is not as interesting as the giant size and fascinating form of the flower. This Indonesian rain forest native sports a huge flower (it is actually many flowers, aka an inflorescence, grouped together on one fleshy axis, what botanists call a spadix) that is unlike any flower that grows in North America. In fact, botanists tell us it is the “largest unbranched inflorescence in the world”. The massive size of the flower is the source of another common name for it, the Titan Arum. That common name was bestowed by the British naturalist and TV host Sir David Attenborough for his BBC series “The Secret Life of Plants”. Mr. Attenborough felt that repeatedly calling the plant by its botanical genus name Amorphophallus (Greek for misshapen phallus) was “too rude for television audiences”.
Readers are likely familiar with other plants that bear spadixes such as the common houseplant, the Peace Lily (aka Spathiphyllum, related to the corpse flower, and also in the Arum family of plants). Unlike the inflorescences of the peace lily which are around 6 inches in length, the corpse flower inflorescence can grow as tall as 10 feet, although the one at the Denver Botanic Gardens (nicknamed “Stinky”), was probably closer to 4 or 5 feet tall. In the center of the flower is the large and somewhat crumpled looking spadix. Framing the giant spadix, is a wine colored skirt-like apparatus that appears to be a type of flower petal, but in actuality is called a spathe. The spathe is a modified leaf which helps protect the spadix.
Aside from the fascinating scale and form of the corpse flower, the rank stench it produced was curious as well. While viewing the bloom, I would describe the acrid scent as similar to an infant’s dirty diaper. There are several repulsive chemicals released during its peak bloom period. Scientists have recorded a range of compounds emitted by the corpse flower that are also found in limburger cheese, animal feces, stinky feet, and dead fish, along with some other not so foul compounds. The exact foul fragrant mix emanating from the flower might vary hourly from rotting fish to rancid cheese throughout the blooming time. All of these nauseating notes are released as the plant is able to heat itself up to 90 degrees Farenheit, helping to volatilize the stench and get noticed by pollinating insects that might pass by. The increased heat of the bloom is theorized to also give the illusion of a recently deceased animal carcass.
Before we look at other stinky flowers, it is interesting to note that there are about 170 other species closely related to Amorphophallus titanum. Botanists report that many of these 170 species emit various unpleasant odors that range from rotting meat to rancid cheese. And size of flower does not translate to the power of stench. Some of the smaller species stink the most. However, some of the 170 species actually smell pleasant to humans, such as A. haematospadix, that smells of banana, and A. manta which smells of chocolate.
While the corpse flower may get all the attention for being one of the world’s most unpleasant floral scents, there are many other fetid flowers that are lesser known, but are just as notable for their “disagreeable odors”. Apparently emitting foul odors has been ecologically successful for several species. And of course, what humans may consider a foul stench, a carrion beetle may interpret as a false “dinner bell”.
Now on to the list of a few of the other unpleasantly scented flowers:
Rafflesia arnoldii – Another so-called “corpse flower”, this one is also native to Sumatra, Indonesia, like the other corpse flower (Amorphophallus titanium) that recently bloomed in the Denver Botanic Gardens greenhouse. This corpse flower is quite rare, and is a parasite on the host Tetrastigma leucostaphylum. It is said to have one of the largest (1m wide) individual flowers in the world, and has no roots or leaves. Most of its life is spent inside the stems and roots of its host. Rafflesia arnoldii only becomes visible when its flower buds break through the bark of the host and form into the large flowers, which like Amorphophallus titanium, also smell like rotting animal flesh. Unlike Amorphophallus titanium, Rafflesia arnoldii is very difficult to grow in cultivation.
Frittillaria agrestis -This flower from the lily family, commonly referred to as stinkbells, is purported to smell like dog feces. It is endemic to California.
Frittillaria imperialis –This is another flowering plant from the lily family, commonly called “emperor lily”. It’s native to Iraq, Iran and other parts of Central Asia, and has showy blooms that have endeared it to horticulturalists who’ve brought it into wide cultivation. The flowers are said to smell like skunk. Others say they have a “distinctly foxy odor” which repels mice, moles and other small animals.
Tree of Heaven (Ailanthus altissima) – This weedy tree, originally native to China, but now present in many urban and other disturbed sites in North America, emits a slightly unpleasant scent from its flowers. The smell is akin to rotting garbage. The leaves and green stems of Ailanthus also smell unpleasant when cut. The Chinese name for this tree, chouchun translates to “foul smelling tree”.
Hawthorne trees – (Crataegus, various species) These beautiful trees are a useful ornamental tree to have in a xeriscape garden. They are tough and beautiful drought survivors. However pretty the white flowers are in springtime, they do not, in my opinion, have a pleasant scent. Some observers have likened it to being like ‘power bait’, the fish lure. Luckily, it is not a very strong or long lived odor.
Lysichiton americanus – Western Skunk Cabbage. This North American native is a distant relative of the Amorphophallus titanum, as they are both members of the Araceae family. It is native to wet areas of the Pacific Northwest. As the name suggests, it emits a “skunky” odor.
These are just a few of the many unpleasantly scented plants to be found in our world. Perhaps you have one you would place in this group of foul smelling botanicals?
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
After a long hot summer in Colorado, the fall season may seem like a time to forget about your yard or garden and start focusing your attention indoors. But fall is a great time for some low-water perennial plants to look their best and shine in your xeriscape garden. The following list of plants take center stage during the fall season, and keep your landscape looking great beyond the arrival of the autumnal equinox.
Anemone (various species and cultivars)
Anemones are a great plant for the shadier areas of your landscape. While not as drought tolerant as the other plants on this list, they grow very well with afternoon shade and a medium amount of water.
Anemone
Tall Sedums, various cultivars
The tall sedums are a classic addition to the fall blooming garden. With low to average water needs, they are perfect for most xeriscape gardens.
This cousin of the popular groundcover plant Orange Carpet California Fuschia (also a good late bloomer) has similar dazzling orange trumpet shaped flowers that pollinators adore.
Hummingbird Flower
Furman’s Red Salvia, Salvia greggii (several species and cultivars available in the Salvia genus)
There are so many different and wonderful plants in the Salvia genus that are remarkable additions to your low-water landscape. Furman’s Red Salvia is one plant we have raved about many times, and it never fails to keep us captivated by its lovely and numerous red blooms that drape these plants from summer heat to fall frost. One note of caution on this plant would be the hardiness. It is rated as only hardy to zone 6, so be careful where you place it. A warmer micro-climate location in your landscape would be best.
Furman’s Red Salvia
Blanket flower, Gaillardia (various cultivars available)
While the blanket flowers bloom more profusely in the heat of the summer, they continue to bloom into fall, bringing their brilliant shades of yellow, orange and red into the shorter days of autumn.
Blanket Flower
Goldenrod, Solidago (various species)
Solidago rugosa ‘Fireworks’ is the plant pictured here. Who wouldn’t mind this kind of fireworks in their fall landscape? This North American native will grace your garden with many panicles of bright yellow flowers. While not as tolerant of drought as some other plants on this list, it is fairly adaptable to most conditions in Colorado. This plant has been unfairly blamed for hayfever and allergies in the past, but scientists now tell us that Goldenrod is not the cause of your fall allergies. It is likely caused by other plants such as ragweed.
Goldenrod
Plumbago, Ceratostigma plumbaginoides
Plumbago is an indispensable groundcover. It does well in dry shade, and that is the type of conditions we typically place it in. However, we are finding it seems to be adaptable to sunnier locations as well. The blue-violet flowers that appear on this plant in late summer are eye-catching, as is the red-orange fall color of the foliage as autumn grows cooler.
Plumbago
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These photos show a sampling of the diversity of color and form that annual Zinnia flowers can exhibit.
I have recently become a fan of the old garden stand-by, the Zinnia. The garden Zinnia was a favorite annual of yesteryear, and seems to be experiencing a resurgence in popularity of late.
The Zinnia genus contains annuals, perennials and shrubs. All the Zinnia species are native to our hemisphere, in an area that stretches from the southwestern U.S. down to South America.
The most common annual Zinnia you can purchase as seed or as bedding plants is likely to be Zinnia elegans or Zinnia haageana. Plant breeders have created many Zinnia cultivars over the years. Annual Zinnias are easy to grow from seed, and do very well in my growing conditions in Colorado.
One thing I’ve only noticed after I started growing them is the great variety of color and form that the flowers exhibit. There seems to be an endless supply of different colors, forms, and sizes that annual Zinnia flowers will exhibit.
The photos shown above are a small selection of the diversity of Zinnias you can grow in your garden. Some of these zinnias I grew from seed in my garden, and some of them are growing in the Denver Botanic Gardens. Most of the Zinnias pictured here are cultivars of Zinnia elegans. A couple of them might be cultivars of Zinnia haageana.
Bees and butterflies seem to love Zinnia flowers, too. The recent migration of Painted Lady (Vanessa cardui) butterflies that passed through Denver, brought a plethora of butterflies feasting on my Zinnias. And in the evening, several bumble bees (genus Bombus) could be found sleeping on the underside of some of the zinny flowers in my yard, after they had spent a busy day buzzing from one Zinnia flower to another.
Zinnias are so easy to start from seed, that I recommend you try to grow some in your yard at the start of the next garden season.
This is the official blog of Outdoor Design Group, Colorado Landscape Architects. For more information about our business and our services, click here.
