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Are All Oak Trees Slow Growing? …No, They’re Not

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.

This is the official blog of Outdoor Design Group, Colorado Landscape Architects.  For more information about our business and our services, click here.

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Hail-proof Plants for your Colorado Garden

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)

Korean Feather Reed Grass

Plants with Grass like leaves:

-Daylilies, Bear Grass (Nolina microcarpa), Desert Sotol (Dasylirion)

Trees and Plants that Leaf out Later:

-Catalpa, Gaura, Datura

Datura

Trees and Plants with Small Leaves:

-Honeylocust (Gleditsia triacanthos), Rabbitbrush (Ericameria nauseosa), some Hysops (Agastache spp.), some Penstemons, California Fuschia (Epilobium canum), Coreopsis

Pineleaf Penstemon

Plants with No or Insignificant Leaves:

– Cacti (many varities), Ephedra, Broom (Cytisus purgans, Cytisus scoparius)

Cylindropuntia cactus

Plants with Tough Leaves:

– Evergreen trees & shrubs (Pine, Spruce, etc.), Agave, Yucca, False Yucca (Hesperaloe)

Agave

Plants that can be moved or sheltered easily:

-Annual/Perennial pots

Pot planted with perennials

This is the official blog of Outdoor Design Group, Colorado Landscape Architects.  For more information about our business and our services, click here.

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7 of the Best Perennials for Fall Blooms in Denver

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.

Sedum

 

Hummingbird Flower, Epilobium canum latifolum (aka Zauschneria canum latifolium)

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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Photo of the Day: Zinnia Floral Diversity

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.

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Photo of the Day: Awesome Artichokes

Many of the annual and vegetable plants at the Denver Botanic Gardens are at their peak right now, and looking amazing. This photo of an artichoke plant in bloom was captured in the garden’s Potager Garden area. Artichokes are typically known as a food crop, with several cultivars grown worldwide, but many horticulturalists like to grow it as an interesting ornamental plant. Their large leaves and spiky flowers add a wonderful sculptural form to the garden. It is my understanding that on a typical artichoke farm, the flower buds are harvested and sent to market well before they open. In these photos we see that the flowers have been allowed to open, providing a stunning display for garden visitors.

Artichokes look a lot like thistles. And it turns out, artichokes are indeed related to thistles, with both plants being members of the very large family of plants that botanists call the Asteraceae.

The historical record holds that artichoke cultivation as a food goes back as far as ancient Greek and Roman times. It is likely that the Greeks brought artichoke cultivation to Italy. Some historians posit that cultivation of artichokes was further developed and improved upon in medieval Muslim Spain. The name artichoke can be traced to the medieval Arabic term “ardi shawki“.

This is the official blog of Outdoor Design Group, Colorado Landscape Architects.  For more information about our business and our services, click here.

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