SITE PREPARATION AND SOIL LAYER BUILDING

OK! So you made it to Site Preparation. Congratulate yourself! You are over halfway there (learning your native and making a naturescape plan are usually more time-consuming). And recognize that now is when the real fun begins - you get to be outside and maybe even get dirty!

The site-preparation you will do (or have done) will depend significantly on your site. It may entail removing trees, killing grass, removing invasive plants (such as English ivy, Himalayan blackberry, kudza, vinca, or other), and amending/restoring damaged or compacted soil, etc. We will focus first on transferring from a grass lawn to a naturescape because that is the situation in which most people find themselves. We will then discuss some of the other situations.

From Turf Lawn to Naturescape
In transferring from a turf lawn to a naturescape it is important to realize that you are not just removing grass and planting natives, but you are restoring the soil or soil "layers" at your site.

To help appreciate what this means, we would like to distinguish between mineral soil and organic soil. We will use the term mineral soil to generally refer to soil that has a low organic component - we often call this "dirt" and it tends to be rather hard when dry. We will use the term organic soil to refer to soil that is comprised largely of decomposing leaves, needles, and other organic material - it tends to be soft and moisture-absorbent.

Organic soil layer - Fingers penetrate easily

Can you remember the last time you went for a walk in the woods or other natural area? What type of soil did you find (assuming you actually looked)? You probably found an organic soil layer of 3-4 inches (generally 1 to 6 depending on conditions) which gave way to a mineral soil layer. You may have also noticed that the herbaceous plants (the non-woody plants that often grow close to the ground) tend to grow in the organic soil layer, while the shrubs and trees tend to grow in the mineral soil layer.

Contrast the local woods or an undisturbed site with a turf lawn. Have you ever driven a shovel into a turf lawn? What soil layers did you find there? We suspect that you found only the mineral soil layer. That is because prior to installing a turf lawn, the organic soil layer is typically stripped off.

While some herbaceous plants can support being planted directly in mineral soil, particularly sun-liking perennials such as grass, etc., most herbaceous plants, particularly the partial-shade and full-shade liking ones (those found among trees and shrubs) need an organic soil layer. Accordingly, if you will have anything other than a full-sun meadow (or sand based "desert-scape"), it is preferable to have an organic soil layer. And, regardless of whether you are planting a full-sun meadow or a partially- or fully-shaded space, there is benefit in establishing at least some organic soil layer because it provides weed-suppression and soil moisture retention.

That is why, in essence, we suggest that in changing from a turf lawn to a naturescape you're not simply switching plants, but rather restoring the soil layers. And don't worry now about how we do that - it is fun, easy and inexpensive and we'll discuss it more below. First, however, let's take out some lawn. … Yeah, let's get out our tools, put on our boots, and go "kick some grass!" [Yeah, we know, cheezy humor, but we couldn't resist]

There are primarily two ways to get rid of grass (1) dig it up, and (2) smother it. If you live in an arid climate there is a third, stop watering and wait. And if you are extremely patient there is a fourth, plant trees and they will naturally kill the grass by shading it out (may take 5-10 years). Here we will discuss the first two, and how to re-establish the organic soil layer.

Digging it up!
When it comes to digging up grass, you will likely need a rototill and rake or for smaller areas or folks who like to do things by hand, a shovel and/or pick and rake. For do-it-yourselfers, local rental shops often carry rototills. The larger self-propelled tillers (12-16 hp) tend to work well for average lawns. Rototills work best when the lawn and soil are somewhat dry. If too moist, you may create a mud bath.

Regardless of whether you use a rototill or do it by hand, thoroughly turn over the soil and rake away the grass. The goal is to remove as much of the grass plants as possible so that the grass does not grow back into the space creating a maintenance issue. After tilling and thoroughly raking you should be left with smooth exposed dirt.

It is important to recognize that if you add water (rain, fog, etc.) to the exposed dirt you often get "insta-weeds" (not having "exposed dirt" is one of the benefits of the smothering technique discussed below). To help prevent or minimize this, we recommended that you be ready to plant your plants and otherwise cover the exposed dirt as soon as possible after it is cleared.

As discussed in more detail below, we recommend that you first plant your trees and shrubs in the exposed soil. Next we recommend that your cover the remaining exposed soil with a material that is both (1) an organic soil layer builder and (2) a weed suppressor. The number one material that we recommend for this is leaf mulch. Our second choice is a thick layer of leaves, though leaves tend to only be available in the fall and are more likely to blow away. Grass clippings and/or straw would be a distant third (distant because it is unnatural to have such a high concentration of cut grass, though the grass clippings could be mixed in with leaf mulch or leaves). Note that if you live in an area that has predominantly needle bearing trees, you can substitute the words "needle mulch" for "leaf mulch" in the present discussion.

Leaf Mulch - Organic Soil Layer & Weed Blocker
Leaf mulch is decomposing leaves and is about the closest commercially available substance to the organic soil layer that you are attempting to replace. Thus, it is the growing medium for a number of plants that you might want to plant. It is also an excellent weed suppressor. In addition, leaf mulch is relatively weed seed-free (leaves are not the reproductive parts of plants) and it breaks down relatively quickly, thereby releasing its nutrients to your desired plants (i.e., a natural fertilizer).

Caution on Yard Compost and No Bark Mulch!
In contrast, try to avoid commercial yard debris composts because they are often of unknown origin and contain weed seeds. The provider may claim that the weed seed are all dead, but in reality that is rarely the case. Also, avoid bark mulch because it is slow to break down, low in nutrient value, supports weed growth, and quickly becomes a maintenance problem. Bark mulch is only popular because it is aggressively marketed, and returns profits to its producers and the maintenance folks that are hired to spray chemicals on it and/or manually pull weeds from it. Large quantities of bark mulch covering ground is also an unnatural condition and thus there are no native plants that evolved to grow in it.

We will discuss below how you might obtain leaf mulch and how you might use it. First, however, let's discuss the other method of getting rid of grass - smothering it - so that you can contrast the two methods and decide what is right for you and your situation.

Smothering It
While there may be a time and a place for removing grass by digging it up, that approach can be fairly labor-intensive relative to smothering it. In addition, and, perhaps of greater concern, digging up grass leaves bare soil which is a magnet for weeds. Thus, the smothering or obstruction method may have its advantages.

The smothering method is pretty straightforward though when practiced most effectively it requires some advanced planning and some patience. A typical approach would be as follows:

Cut the turf grass to the lowest setting on your mower and then cover it with newspaper at a thickness of 10-16 sheets. Be sure to overlap the newspaper sufficiently so that cracks don’t appear through which grass and weeds can grow. This starts the smothering process. Next, apply either several inches of leaf mulch (4-6 inches) or a thicker layer (6-8 inches) of leaves alone, or a combination of the two. If you use leaves, it is a good idea to wet them down so that they will stick together better. Note that while 6-8 inches of leaves might seem like a lot, a good rain may reduce that height in half.

Using newspaper and leaves to smother grass.

The layer of leaf mulch or a greater thickness of leaves alone works in combination with the newspaper to block photosynthesis, which effectively kills the grass. The leaf mulch and/or leaves also provide the organic soil layer (the leaf mulch more rapidly than the leaves). The newspaper (a wood product) will breakdown and also contribute to the organic layer.