Friday, April 27, 2012

How Many Plants Do I Need?

I received a question about my Planning Your Landscape Improvements post asking how to figure out how many plants to install in the outlined “blobs” used to represent perennials and groundcovers on the example landscape plan.  Perennials and groundcovers are often graphically represented as general outlines on plans rather than as circles like trees and shrubs to keep the drawing from becoming too busy with many tiny circles for each individual perennial or groundcover plant. 

To determine the number of individual plants needed for the massing, you first have to determine the area of the space to be planted based on the general shape of the planting bed.  I apologize in advance, because there will be quite a bit of math in this post.
If it’s been a while since your last geometry class, determine the area (square footage) of the space to be planted using the formulas for each of the respective shapes shown below:
Area of a square or rectangle = length (L) x width (W)
Area of a triangle = 1/2 [length (L) x width (W)]
Area of a circle = 3.14 (Pi) x [radius (R) x radius (R)]
The area of plantings wrapped around the base
of taller plants can be calculated as a curved rectangle (L x W)
For more complex shaped beds, a combination of area calculations must be added/subtracted.  In this example, the plantable area can be broken down into four basic shapes: two circles and two triangles.  The areas of the two triangles would be added to the area of the larger circle. Then the area of the smaller circle at the base of the tree would be subtracted from that total, since you can't plant on the trunk/root ball.
Once you have your total square footage to be planted, you need to know the mature spread (width) of the plant species you will plant in that space.  A plant's size at the time you buy it will not be the same after a few months, or even weeks, of growth. You need to take that growth into account.  The plant's mature size information is often listed on plant tags in nurseries or garden centers, or you can look it up (plant information). The mature spread of the plant is how far apart you should plan on spacing the centers of plants from each other so they have room to mature and not look overcrowded.
View of the top of a plant from above
Once you’ve determined how far apart to space the plants, find the corresponding division factor for that spacing from the listing below:

4” - 0.11

6” - 0.25

8” - 0.44

10” - 0.70

12” – 1.0

15” – 1.56

18” – 2.25

24” – 4.0

30” – 6.25

36” – 9.0
Divide the total square footage to be planted by the division factor, and the result is the quantity of plants needed to fill your area at that particular plant spacing.  For example, if I need to plant 50 square feet with plants evenly spaced 18” apart: 50 / 2.25 = 22 plants.
These factors assume a triangular plant spacing, which provides a more dense and full appearance than square spacing.
Division factors are based on triangular plant spacing.
Square plant spacing does not look as full and dense as triangular spacing.
Now that you’ve invested all this hard work figuring the quantity of plants to perfectly fill your planting bed, be sure to maintain the same discipline when planting them.  By that, I mean use a tape measure ensure your spacing is correct and consistent during installation.  If you try eye-balling it, you’ll probably end up with too many, too few, or unevenly spaced plants when you reach the end of the planting bed.

Friday, April 20, 2012

Invasive Species Alternatives

The term “invasive plant” refers to a species that propagates and spreads so rampantly that it crowds out other types of plants, reducing what ecologists refer to as biodiversity. Most invasive plants are exotic species, or plants that were brought to a region from foreign lands. The exotic plants are able to survive in the new region because of similar climatic conditions to their native area. However, the plants did not evolve in conjunction with the other flora and fauna in the new region, so the natural system of “checks and balances” that keeps species from becoming over-populated does not affect the exotic species. In essence, the invasive exotic species becomes a bully who kicks everyone else out. 

Now, not all exotic species are invasive, and I do not advocate always using native species exclusively. We in the landscape business would be hard-pressed to find appropriate evergreen shrubs for various situations without varieties of yews, junipers, and boxwoods –many of which are cultivars of exotic species but are not invasive. However, there are numerous exotic species that have proven themselves as invasive yet remain popular in the landscaping trade. My intent with this post is to inform you of some of these invasive species that may be on your plant list for this year’s landscape improvements and present you with non-invasive alternatives to use instead. One key point to keep in mind is that invasive species do not necessarily appear overly-aggressive, spreading, or colonizing on your property. However, as their seeds are spread by animals and wind to natural areas (wooded areas, grasslands, wetlands, etc.) they quickly grow, spread, and reduce biodiversity.

Invasive Species: Purple Norway Maple
(Acer platanoides hybrids)
Norway Maple
image courtesy Missouri Botanical Garden Plant Finder
Native to Europe (go figure, with a name like Norway Maple), this tree species gained popularity in the landscaping trade due to its tolerance for a variety of unfavorable soil and water conditions where many other species won’t thrive, as well as the unique purple-red foliage of many cultivars. These unique characteristics have caused the species to become over-planted in many developed areas. Norway Maples easily self-propagate via seeds carried by wind-blown samaras (“helicopters”). Once introduced to naturalized areas (forests, grasslands, wetlands), the dense shade from the trees’ canopies prevent growth of desirable native species.
Alternative: Thornless Honeylocust (Gleditsia triacanthos var. inermis) or Kentucky Coffeetree (Gymnocladus dioicus)
         Honeylocust                                                                                  Kentucky Coffeetree
Images courtesy Missouri Botanical Garden Plant Finder
honeylocust link
coffeetree link
Both of these species are North American natives that offer a similar tolerance for tough urban conditions as Norway Maples, although they do not have purple foliage. Both of these species are readily produced in the nursery trade, so availability should not be a problem.

If a tree with purple foliage is critical, try Rivers European Beech (Fagus sylvatica ‘Riversii’). Although not native to North America, this species is less aggressive than Norway Maples and displays similar purplish red foliage. However, this tree will not tolerate wet or compacted soils, so avoid planting in heavily urban conditions.
Rivers European Beech
Image courtesy Missouri Botanical Garden Plant Finder

Invasive Species: Burning Bush
(Euonymus alatus)
Burning Bush
image courtesy Missouri Botanical Garden Plant Finder
This shrub species is overused because it is very adaptable to a variety of conditions, has good form, and displays bright red fall color (hence, the common name). An exotic species native to Asia, it has a tendancy to spread to natural areas by way of birds feeding on its seeds. Once established in these natural areas, the shrub's aggressive nature chokes-out more desirable native species, reducing biodiversity.
Alternative: Red Chokeberry
(Aronia arbutifolia ‘Brilliantissima’)
Red Chokeberry
image courtesy Missouri Botanical Garden Plant Finder
This shrub species is a cultivar native to North America. It reaches a similar mature size as Burning Bush, displays bright red fall color, showy white spring flowers, and red berries in winter.
Invasive Species: Ornamental Pear Tree
(Pyrus calleryana Hybrids)
Callery Pear
image courtesy Missouri Botanical Garden Plant Finder
Native to Asia, the Callery Pear gained popularity in this region for its adaptability, urban tolerance, white spring flowers, and purple fall color. Numerous hybrids have been developed that were thought to be fruitless and sterile. Unfortunately, because they are so over planted in urban areas, these sterile hybrids can actually cross-pollinate with different varieties and have evolved to produce fruit. Birds eat the fruit and spread the seeds to naturalized areas where they choke-out native species and reduce biodiversity.
Alternative: Autumn Brilliance Serviceberry
(Amelanchier x grandiflora ‘Autumn Brilliance’)
Autumn Brilliance Serviceberry
image courtesy Missouri Botanical Garden Plant Finder
Although only reaching a mature height of 15-25 feet as opposed to 30-40 feet of Pear Hybrids, this species is adaptable to a variety of soil conditions. It produces white spring flowers, bright red fall color, and purplish-black berries that attract birds. Autumn Brilliance Serviceberry is a hybrid cross between Amelanchier arborea and laevis, both native to North America.

Invasive Species: English Ivy
(Hedera helix)
English Ivy
image courtesy Missouri Botanical Garden Plant Finder
This evergreen vine is native to Europe. It spreads easily by cuttings or by seed dispersed by birds. English Ivy will naturalize in woodlands, spreading very aggressively and smothering native understory plantings.
Alternative– Virginia Creeper
(Parthenocissus quinquefolia)
Virginia Creeper
image courtesy Missouri Botanical Garden Plant Finder
While not evergreen, this North American native vine is easily established and displays excellent red fall color.
Invasive Species: Purple Japanese Barberry
(Berberis thungergii var. atropupurea)
Purple Japanese Barberry
image courtesy Missouri Botanical Garden Plant Finder
Native to Asia, this shrub is popular in the landscaping trade for its unique purple-red foliage that provides contrasting color interest against the typical green foliage of most plants. The plant produces berries that attract birds whom spread the seeds to naturalized areas where the plant crowds-out native species.
Alternative: Purple Ninebarks
(Physocarpus opulifolius ‘Diabolo’,‘Center Glow’, ‘Coppertina’, or ‘Seward’)
Diablo Ninebark
image courtesy Missouri Botanical Garden Plant Finder
These cultivars of the North American native shrub offer purple foliage similar to Barberries without being invasively aggressive. Different cultivars have different forms and sizes, so a viable Ninebark substitute for Barberries can be found for most any situation where unique foliage is desired.

Friday, April 13, 2012

Planning Your Landscape Improvements

Being a landscape architect, I don’t want to sound too “preachy” on the subject, but having a plan for your landscape improvements is critical before you start any work.  You wouldn’t build an addition to your house, or even a shed, without some form of plan to serve as a guide, so why take an improvisational approach to the landscape?  Much like a strategic plan for a business or a financial plan for a household, a landscape plan serves as the guiding perspective for your work.  It allows you to logically phase your efforts and budget over time while providing maximum impact during the interim.  It will also help avoid a cluttered appearance of numerous hardscape, planting, and focal features crammed in wherever space seemed available.

Here is an example of a residence’s overall master plan for the landscape, the “grand vision” the owners would like to someday realize.  However, these owners do not currently have a “grand” budget, so the subsequent plans illustrate how portions on the overall master plan will be installed logically over several planting seasons.  This allows for maximum impact of available resources while providing a foundation on which to build future additions.
LANDSCAPE MASTER PLAN (click here to enlarge)
The "grand vision" the owners are working towards.

PHASE ONE (click here to enlarge)
Plants shown in color are installed during the first planting season. 
The owners' modest budget is maximized by installing plantings
at key locations that can be built upon in the future.

PHASE TWO (click here to enlarge)
Plants shown in color are additions installed during the second planting season. 
They add another layer of interest to the plantings installed
the previous year (shown in black and white).

PHASE THREE (click here to enlarge)
The third planting season brings additional plantings to expand
existing beds and create more layering of form, texture, and seasonal color.

PHASE FOUR (click here to enlarge)
The final planting additions round-out the overall master plan for the property. 
Each of the previous phases were modest and manageable efforts that
established the backbone for the completed product. 
However, the previous phases looked fine standing on their own without the future additions.  
Flexibility is incorporated into the plan.  General categories of plants (shade tree, ornamental tree, deciduous shrub, evergreen shrub, etc.) or a variety of species options are noted for many of the plantings.  This provides the owner flexibility in anticipation of plant availability options from various retailers, community group plant sales, or a friend or neighbor offering plant divisions.  These plants can be installed in a designated location per the plan based on the ornamental value (height, form, texture, color) and horticultural requirements of the plant (sun exposure, soil moisture, space to grow).

If you plan on installing most landscape improvements yourself, your plan doesn’t have to be graphically fancy or professionally produced.  It can be a simple sketch on notebook paper – just as long as it’s legible to you.  If you aren’t confident with your design capabilities, want some fresh ideas, or intend on having the improvements installed by a contractor, then I do recommend having the plan professionally documented by a landscape architect, landscape designer, or professional gardener.  Also, if any landscape improvements require permitting from your municipality or approval from a homeowners association, then a professionally produced plan may be required by those agencies.  Check the requirements of your local governing agency to be sure.  Finally, always have your local utility company locate and mark all buried utility lines on your property before beginning work.