(Editor's Note: This article was originally published on April 10, 2010. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I'm sure all gardeners are familiar with Colorado blue spruce, Picea pungens var. glauca. They are among the # 1 landscape tree for large parks and gardens throughout temperate regions of the world. In December 2008, Geoff Stein (palmbob) wrote a wonderful article on Blue Conifers Choices for the Holidays. This article mentioned a few of the many blue spruce cultivars which exist but as he mentioned, there are far more. This article will go into more depth the wonderful array of blue spruce that you may find in your local nurseries.
As the common name suggests, Colorado spruce is native to Colorado. In fact, they are found wild from Idaho and Wyoming in the north, south through Colorado, Utah, Arizona and New Mexico, growing in mountainous regions. This coniferous tree can reach 40 m (130 feet) in the wild but in cultivation they rarely exceed 25 m (80 feet). The normal species has bluish new growth that fades to green over the winter months. Many gardeners get fooled by this. They purchase a Colorado spruce, thinking it will be blue year-round, only to find it has turned green by spring. No, the plant is not suffering for any nutrient deficiency and adding aluminum sulphate (the chemical that keeps your Hydrangeas blue) will not make it turn back to blue. You simply bought just the regular Colorado spruce, not the BLUE Colorado spruce which is Picea pungens var. glauca. It is important to read the tag! (assuming the plant has one). To ensure you have a REAL blue spruce, you are best to purchase one of the named selections which are generally grafted, therefore true to form.
Above are two examples of the lovely dwarf form called 'St. Mary's Broom'
In cultivation, they require full sun and well-drained soil. While they perform admirably under acidic soil conditions, they seem to prefer more neutral to slightly alkaline soil. Colorado spruce are very drought resistant and reasonably tolerant to salt. They are hardy from zones 2 to 8. The blue colour comes from a waxy layer on the needles. In wet climates the wax can be partly lost, dulling out the ‘blue' effect. In dry climates, the wax remains year-round thus plants in the mid-west are often much "bluer" than the same plant growing in the Pacific Northwest or northeastern North America.
There are nearly 100 named selections of Colorado spruce (not all are ‘blue' spruce), which can range from under 1 m (3 feet) to towering giants. Most are much too large for the average garden lot so care must be taken to select a smaller form if you do not want to risk the tree outgrowing its allotted space. While there are several green forms and even yellow forms of Colorado spruce, this article will focus just on the "blue" types.
For larger spaces, the premier blue cultivars are 'Koster', 'Hoopsii' and 'Moerheim'. Other larger selections you may encounter include 'Copeland', 'Endtz', 'Fat Albert', ‘Ice Blue', 'Mission Blue' and 'Oldenburg'. If you prefer tall but narrow form, then 'Fastigiata', 'Iseli Fastigiata', 'Columnaris' or 'Thomsen' are your best choices. There are a few weeping forms. These may seem small when first purchased but can get quite large over time, both in width and height. These Dr. Seuss-looking trees include 'Pendula', 'Glauca Pendula', 'Kosteri Pendula' and 'Shilo-weeping'.
Standard cultivars include 'Moerheim', 'Fat Albert' and 'Hoopsii'
Above are two examples of 'Glauca Pendula'
So what can you choose from if you have a more typical garden lot. There are several semi-dwarf selections that are upright. These often appear more globe-shaped when young but develop a leader with age. They will eventually reach 6 to 10 feet, but they are slow growers. Ones to look for include 'Glauca Compacta', 'R. H. Montgomery', ‘Jack Corbet', 'Thume' and ‘Hunnewelliana'. The smallest selections will often stay under 1 m (3 feet) thus are suitable for rock gardens and foundation plantings. These include ‘Hillside Dwarf', 'Glauca Globosa', ‘Jean Iseli' and 'St. Mary's Broom'. If you prefer the groundcover effect there are a couple of prostrate, ground-hugging forms namely 'Glauca Procumbens' and 'Glauca Prostrata'. The dwarf globular forms are often top-grafted to produce blue lollipop conifers while the prostrate forms may be top-grafted to produce dwarf weeping forms.
A selection of semi-dwarf and dwarf blue spruce include 'R. H. Montgomery' (top left), 'Jack Corbert' (top middle), 'Thume' (top right), 'Glauca Globosa (bottom left and top grafted specimen bottom middle) and 'Glauca Procumbens' (bottom right)
There are no doubt other Colorado blue spruce selections that I have not mentioned. New ones seem to crop up almost yearly. It is worth visiting your local nursery to see what they offer if you are in the market to obtain one of these striking conifers. But please do some research as many of these innocent-looking small conifers can become quite large and will look horrible if you have to continually prune them!
I would like to thank the following people for the use of their pictures: conifers ('Glauca Prostrata', Jack Corbet', 'Moerheim'), Equilibrium ('Glauca Pendula'), Gustichock ('Glauca Globosa), secludedgardens (top grafted 'Glauca Globosa') and slyperso1 ('Glauca Pendula' and 'Thume').