John C. Fech
Horticulturist, ISA Certified Arborist
University of Nebraska
Regardless of the mix, the goal for green minded gardeners is to grow, plant and care for healthy landscape plants and turf. One of the most important factors in the success of these endeavors is getting to know specific needs of the plant material and how they can be combined effectively in a landscape without compromising the needs of each component.
As you read this, you may be asking yourself if I'm over-doing it a bit, making too much out of the importance of separating them. I respect that. These days, a healthy skepticism of everything you read and hear is a valuable mode of operation. So, humor me. Read to the end of the article and then re-evaluate your thoughts. I'm sure you'll be convinced of the basic premise.
Ornamentals and turfgrasses are very different plants; different needs, different preferred growing conditions, different functions. Turfgrasses are generally full sun plants. Ornamental plants vary in preferred light conditions, from full sun to heavy shade. The need for added nutrients is another big difference. Once established, most trees, shrubs and flowers can get by just fine on the native soils, requiring supplemental fertilization only if a deficiency develops such as iron chlorosis. Turf, on the other hand, requires periodic applications of nitrogen and other elements to grow thrifty. Some turfs need more than others, and some clients prefer the thick dark green lawn that results from more abundant fertilizer, but all turfs require more.
Soil moisture is another big area of difference. Although both groups require moisture, the need for addition is generally greater with turfgrasses – on average twice as much more. The roots of most trees grow thick and lateral, like a pancake in the upper 18 inches of soil. They have the capacity to draw upon a large reserve of soil moisture to provide water for essential functions of respiration and photosynthesis. While some species (buffalograss, bermudagrass, tall fescue) have a deep root system, they still must be irrigated frequently to survive. Many water thrifty flowers such as coreopsis and rudbeckia simply don't need much water once established, and will actually decline if provided with as much as the turf needs.
Failure to maintain a landscape with the basic premise as a guide can lead to many problems. When trees, shrubs and flowers and turf are co-located, the management requirements of each tend to compromise the other. Many homeowners complain when the grass that's growing under a shade tree becomes thin and weak. A compromise step might be to consider renovation to a shade tolerant species such as turf type tall fescue or fine fescue, but chances are good that the best solution is to create a natural mulch expanse under the tree and forget about the grass.
The difference in the need for irrigation is a significant factor, especially when trees are young and don't create too much shade for the grass. As mentioned above, frequent irrigations are necessary for turf. When trees grow in a turf stand, the irrigation distribution (getting the same amount of water applied equally over the entire grass surface) is poor. A tree standing in the spray pattern will cause distortion of the water throw, causing too much on one side of the tree, and not enough on the other. Additionally, repeated blasts of water on a tender tree trunk can cause significant injury to the bark, and possibly kill the tree.
Certain other turf maintenance operations are not tree-friendly. Another cause of bark injury is mechanical weed whip abrasion, a common occurrence when poorly trained technicians attempt to trim grass growth around the base of a tree. Broadleaf weed control applications to kill dandelions, clover and plantain sometimes harm tree roots growing in close proximity to grass roots.
When ornamentals are over-watered, two outcomes are likely: root rot and over-abundant growth. In landscapes where there is poor soil moisture drainage, tree or flower roots stay wet too long, leading to decay of the root hairs and feeder roots. These important structures are vital to the extraction of moisture and nutrients from the soil; without them, trees will die. If the soil drains adequately, but the tree roots still get more water than they need, the shoots may grow faster and longer than normal. This may sound good at first; however, it usually comes at the expense of essential accumulation of carbohydrate reserves. The reserves are needed to ward off insect attacks, compartmentalize wounds and help the tree survive during stress periods.
Are you convinced yet? How about when you want to have a dinner party at your place, and someone suggests bocce or croquet? It's pretty tough to play lawn games when the lawn is dotted with trees or shrubs, scattered hither and yon. Nothing against either group of plants; it's just that they should be separated.
What to do
As your thoughts shift from the basic premise to the actual reality of the arrangement of hardscape and plant materials in you or your client's landscapes, you're probably left with the quandary, "So, now what?" Two options are clear. One, wring your hands in angst knowing full well the ramifications that a poorly designed landscape creates. Two, think optimistically and creatively. That which seems like it would be a big problem can turn into a new landscape look for you.
Start by performing a site assessment: an honest and thorough evaluation of the status of each part of the landscape. Actually, it's best to break it into two separate operations: a site assessment and a site analysis. Conduct the assessment by making notes on a clipboard. Use phrases to describe each area that simply state the obvious, such as "mildew on turf, crown dieback on redbud, root rot on rudbeckia, exposed roots on maple, canker on trunk of douglas fir, heavy shade under oak and so on. This format allows to you to quickly document the potential renovation areas of the landscape.
After the assessment, walk and talk with a friend or neighbor to embellish the initial notes to include a value judgment on each item. Suggest that the slope might be causing the failing turf and ask for affirmation. Change a phrase like "crown dieback on redbud" to "crown dieback on redbud – I never liked that thing anyway!", or "crown dieback on redbud – Oh, that was a gift from our Uncle Conrad and Aunt Ginny, and they're not with us any more". Getting this type of feedback really helps to sort out the real issues of the landscape, and priorities of your family.
Next, take your notes to a landscape designer at a full service garden center and ask them to draw out several options for fixing the problem. Try to avoid the temptation to plant a whole bunch of perennials under the trees to replace the sickly sod that you're going to mulch over. As stated earlier, the roots of most trees grow in the upper 18 inches of soil, thick like a pancake - spreading out to at least twice the width of the dripline. Activities such as tilling, soil additions placed over the top of the existing grade, Roundup application or even the digging of holes to install shade-loving perennials can damage essential tree roots.
In most situations, tree removal and turf removal are inevitable. Sprinkler re-alignment is also likely, especially if new landscape beds are installed or ripped out, or if removal of a tree means that a shady spot is now a sunny spot.