Friday, May 25, 2012

The Rule of Odd Numbers

A basic rule of thumb in landscape design is to work with odd numbers when trying to create a naturalistic appearance, as opposed to using even numbers which look formal, symmetrical, and regimented. Plant in groups of three, five, seven, or nine as opposed to two, four, six or eight.   This is because even numbers are subconsciously divided into equal halves by the mind to reinforce a man-made, orderly aesthetic.  Odd numbers cannot be subconsciously divided into equal halves, so the composition is interpreted as more naturalistic and the mass appears more unified.  
This arrangement of four shrubs can be visually divided into equal halves by the mind.
Since this arrangement of five shrubs cannot be divided into equal halves, it has a more unified, natural appearance.

This is a useful design rule to keep in mind because most homeowners are not trying to create a formal aesthetic with their landscape design.  The terms “naturalized”, “flowing”, and “softened” are common adjectives used to describe many homeowners’ landscaping objectives, all of which are reinforced with an odd numbered design approach.  This rule of working with odd numbers does not just apply to plants.  It also works with hardscape elements as well such as accent stones, planter pots, and elements within focal features.

Here is a side-by-side comparison of a home’s foundation planting using two trees versus three.  The two-tree arrangement reads as halves, while the three-tree arrangement appears more balanced and unified.
Scale is a factor to consider as well.  Arrangements of threes, fives, sevens, and nines are the quantities you’re dealing with for small scale designs.  For large scale designs, it’s more about the overall quantity of drifts and masses – three, five, seven, or nine different visual masses of plants.  Whether or not the mass has 54 or 55 of a particular plant is irrelevant, but whether that mass is paired with one, two, or three other species masses is important in maintaining a naturalistic aesthetic.
So, keep the rule of odd numbers in mind as you’re designing your landscape, purchasing plants and pots, or dividing perennials.  Unless you are intentionally trying to create a formal design, you're better off sticking with odd numbers.

Friday, May 11, 2012

Mulch: the good, the bad, and the ugly

Laying mulch is one of those on-going landscape maintenance tasks that isn’t much fun, but is extremely important from horticultural and aesthetic standpoints. Mulch’s basic horticultural functions are to retain moisture in the soils around plant roots, insulate plant roots from temperature extremes, prevent weed growth, and add nutrients back to the soil through decay. The simple task of mulching also rejuvenates the appearance of landscape beds.
All mulches are not the same, and they do not all offer similar horticultural or aesthetic advantages. As a rule, I only use and specify shredded hardwood mulch for traditional landscaping applications. For green roof applications where weight is a factor or for bioswales susceptible to washout, expanded shale can be used for mulching.  However, most residential applications don’t have to deal with these issues, so I recommend using only shredded hardwood mulch.
Shredded Hardwood Mulch
Good, well-rotted, shredded hardwood mulch contains pieces ranging in size from a few inches to a fraction of an inch in length and is dark brown in color. It is cost effective, aesthetically attractive without being over-powering and detracting from the real show (plants), and horticulturally beneficial.  Some of the other products on the market that I do not recommend are:

Wood chips
Wood Chips
Wood chips don’t break down as quickly as shredded hardwood mulch, so frequency of re-application is reduced. However, by not breaking down, it isn't replenishing needed nutrients. Fresh, un-aged wood chips also do not absorb as much water as porous well-rotted mulch, reducing their ability to retain moisture around the roots of plants.

Colored mulch
Colored Mulch
In my opinion, the focus of a planting bed should be the plants, not glaring red or orange mulch. Adding chemically-colored mulch makes a landscape look clashingly unnatural. Also, many of the dies used to color the wood are toxic, so whatever you do, keep these chemical dyes away from any soils where edible fruits and vegetables are growing.

Stone mulch
Stone Mulch
True, you only have to lay rocks once and never think about them again, but rocks don’t retain moisture and they magnify temperature extremes on roots. Stone mulch also comes in a variety of colors, which can inspire your design ambitions, but see my reasoning against colored mulch above.

Rubber mulch
Rubber Mulch

This product has been pitched as “green” because it finds a use for used rubber tire waste. However, there are reasons tires have to be specially disposed of, all of which are reasons not to spread pieces of tires around your landscape. Rubber does not retain moisture (which is why we use the stuff for waterproofing). Rubber does not moderate the temperature of plant roots; rather, it increases temperatures through solar heat gain. Rubber does not add nutrients to soil as it breaks down; rather, it adds toxins. It does control weed growth, but one outta four ain’t great. The build-up of used tire waste is an environmental issue that needs a viable solution, but rubber mulch isn’t it. If they told you spent uranium chunks were good mulching material, would you believe them?

Friday, May 4, 2012

Planting Instructions

How to properly “plant” a plant is often a question from those new to the do-it-yourself landscaping game. New-bies shouldn’t be ashamed of this question, because proper initial installation is critical to the long-term health and survival of your plant material investment. There's more to it than digging a hole and making sure you finish with the green-side-up.  Here are general guidelines for proper plant installation:

Hole width:
The hole the plant will be installed in should be at least twice as wide as the root ball or container of the plant, which will vary depending on the type and size of plant. This allows roots to be surrounded with ample non-compacted backfill for roots to grow in as the plant adjusts to being transplanted.
Hole should be at least twice as wide as the root ball for balled and burlapped plants.

Hole should be at least twice as wide as container for container grown plants.

Hole depth:
The hole should be no deeper than the height of the bottom of the root ball to the root collar of the plant. The plant’s root collar is where the bottom of the trunk or stems transition to roots, or, more generally, where the plant emerges from the soil. This is a critical zone of the plant that you do not want to cover with soil or mulch. If you dig the hole too deep, add back soil to the bottom of the hole in 2"-3" layers and stomp to compact. Backfilling and compacting in layers ensures better compaction so the soil won’t settle over time.

Hole should be no deeper than the height of the root ball or container of the plant.

Root ball:
For container-grown plants, “tease” outer roots after removing the plant from the container and prior to positioning the plant in the hole. This prevents the roots from continuing to grow circularly around the plant and “girdling” it as it matures.
"Tease" the roots of container grown plants to prevent the roots from continuing to grow circularly and possibly girdling the plant as it matures.

For balled-and-burlapped plants, position the plant in the hole, cut and remove all cords around the rootball, pull back and push down the top half of the wire basket (if present, on large plants only), and fold the top half of the burlap down.

Remove twine cords and peel down burlap on balled and burlapped plants.

Since securing burlap around root balls at the nursery pushes loose soil towards the stem of the plant, push any excess dirt away from the stem or trunk to reveal the plant’s root collar. This is not often done, even by some professional landscape contractors, but ensures the root flare is not buried too deep.
Push excess dirt away from trunk to expose the root flare.

Back-filling hole:
There is debate in the landscape industry about two extremes for backfilling the hole around the root ball. One side prefers to use none of the soil excavated when digging the hole, opting to backfill completely with new amended topsoil (black dirt mixed with compost or soil conditioner). The theory behind this method is that the plant is under stress from being transplanted, give it the highest quality growing media in which to adapt and don’t trust that the soil excavated from the site has sufficient horticultural properties (anyone disgusted with the depth of topsoil in their yard before hitting clay can understand this). The other side advocates only using excavated “parent” soils when backfilling around root balls. Their point is that plants are usually transplanted when they are young and adaptable, so get them use to their permanent growing conditions as soon as possible. “Coddling” them with superior soils during early growth leaves them susceptible to “shock” when their roots begin to grow beyond the limits of the amended backfill. I prefer the middle ground and recommend mixing amended soil with the excavated soils at a ratio of about 1/3 amendments:2/3 excavated parent soils. Backfill in layers of 4”-6”, compacting each layer with your foot (for larger plants) or your fist (for smaller plants) around the entire root ball until you have backfilled flush with the top of the hole.
Backfill hole in 4"-6" deep soil layers, compacting each layer thoroughly to prevent settling.

Saucer ring:
Form a 3”-4” tall mound with the excess excavated soil around the entire outer ring of the filled hole. This creates a “bowl” to concentrate water percolation to the root zone and prevent wasted run-off.
Form a saucer ring with the excess excavated soil.

Cover the entire diameter of the back-filled hole and saucer ring with 3” of mulch, except for immediately adjacent to the trunk or stems, which should be clear of any mulch. One of the most common mistakes I see in plant installations is excessive mulch mounding around the bases of plant trunks and stems. This can result in fungus, pests, and other problems at the critical root collar zone of the plant.
Add a 3" deep mulch ring around the plant, but keep mulch away from the trunk.

Apply ample water to thoroughly saturate the mulch, rootball, and backfilled soils. The saucer ring should keep most of the water contained around the root ball.  Keep the plant sufficiently moist during establishment.