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  • Writer's pictureEden's Garden Design

Various Soils of Utah

Updated: Jun 7

At one time in our geological history Salt Lake and Utah County valleys were Lake Bonneville. Rivers fed into the lake bringing soil, sediments and vegetation from the nearby landscape, now our majestic mountains. Once the waters receded, we were left with the soils found at the bottom of a salt lake, which include swirls and pockets of silt, clay, sand, and even gravel and boulder beds. Depending on the location of the valley, you will find large deposits of each individually and in rare cases a good mix of them. The perfect soil would include a good mix of these various soils. 80% of your battle in growing a thriving landscape is determined by the soil you have, and if you are lucky enough to live in one of these rare pockets, you will be able to easily grow most plants. If you are not so lucky, you have a few challenges to create a thriving landscape.

Regardless of having great soil, we are the base of a salt water lake and therefore, have an even greater obstacle to overcome. With all of the turbulent geological past for Utah, we have ended up with very alkaline soils. Even if you have a pocket of the perfect soil, your alkaline level will still be on the high side. Generally speaking most of Utah is an 8.4pH on the scale, and the most commonly requested plants prefer 6.5-7pH. Even if we added huge amounts of compost and sulfur to our soils, it will never stay at that preference level.

So now that we know what we face, how do we create a thriving landscape? The most simple solution is to plant only native plants in your landscape, which can be amazingly beautiful as well as easier to maintain. The second path is to improve the soil structure in your yard. Although more work is involved, this option is the greatest step towards mitigating the unique situation of our soils. A strong soil will provide the best foundation for that perfect yard. Several important things to consider as part of a healthy soil are; avoid disturbing the soil once improved, choose the right plants for the space, and to make the beds deep enough for proper root growth

For those wanting the simplest solution, stick with native plants. They do well in the generally poor soil of the state, especially sandy soil. But be aware, that most native plants will die off in enriched soils. But there are numerous trees, shrubs, bulbs, perennials, ornamental grasses that will have no problem growing in most soils found in our yards. Some of the best options include Serviceberry trees, pine trees, juniper trees, currant shrubs, sumac shrubs, little bluestem grass, and grama grass, many types of penstemon flowers, and many more to choose from. Generally, they also more drought resistant which always helps relieve stress on the wallet as well as our water recourses. The only trick is finding them. Most nurseries are starting to carry more native options, but not all of them. Be sure to call around to any nurseries before visiting them.

If you would prefer to grow other plant options in your yard, you will want to improve the structure of the soil. The first step is to find out the current disposition of you soil. The best ratio of soil to grow the exotic plants that will survive our alkalinity is 20:40:40 of sand, compost, and topsoil (mostly clay) respectively. The easiest way to figure out how your soil is laid out is to dig a hole at least a foot deep. If you hit a bunch of gravel, congratulations, you have rocky soil. Next, take a large handful of the actual dirt and add it to a jar half full of water. Let it sit for a day or two until the soil settles to the bottom. The individual components will settle at different rates. The sand is heavier and settles first, then the silt and the clay last. The thickness of each will give you an idea of the ratios. Next is to do the high level math to find out how much, if any, of each type will need to be added to reach that ideal stated previously. For example, if you have mostly sandy soil, you will want to add compost and some topsoil. Clay and silt will be in every type of topsoil available so be aware of that when doing the calculation. Also, you don't need to worry about making it exact. Just do your best to get it close. Your goal will be to fix at least the top six inches of the soil.

Example. Thankfully, your soil doesn't have much gravel but you find that your soil sample has twice as much clay as sand and there is almost no compost. So, lucky for you, the only thing you need to add is compost. Since the clay is already double the sand, you will simply need to add compost to equal the amount of the clay. (2:0:4 is the starting ratio, so simply add compost to reach 2:4:4)

Six inches would be the minimum you would want to do. If you can go deeper, that would create a greater impact. Most perennials and grasses grow approximately 1-2 feet deep. Trees and shrubs 3-5 feet deep. Mixing as deep as you can manage will benefit them proportional to the depth. If you have a mature landscape and digging everything up simply isn't an option, adding compost in the beds annually will eventually mix down into the soil below. Obviously, this method will take several years to make an impact, but the results are worth it.

Remember, the soil structure is vital for plants to flourish. Roots need soil as much as they need air and moisture. And each type helps with the various aspects of that growth. Sand gives air pockets and drainage. Compost helps with moisture and nutrient retention. And topsoil gives stability for the roots to grasp. Having the right mix will create the best potential for best growth, even if it can’t be the best pH level. 

It may seem to go without saying, but once the soil is the great structure, you will want to avoid disturbing it. This is usually easy if we plant trees, shrubs, ornamental grasses and perennials. But if we plant annuals and vegetables, we often think a good annual tilling of the soil is required. That is simply not true. Tilling brings weed seeds to the surface, destroys soil structure, and disrupts the natural microbes and earthworms growing in the area. You need all of those items undisturbed to create a healthy ecosystem in your soil. If you are installing new plants regularly, try just adding compost to the surface. Then do your best to disturb as little of the soil as possible. This will help keep nutrients and moisture at root level.

Another important step in creating a thriving landscape is to choose the right plants for each bed. Trust me, I know the feeling of seeing a beautiful plant in the nursery, but be mindful of the spacing we have and the long term health of the plant. It won't do us any good to get a plant that looks great but dies in a few weeks. Several factors will help you narrow down your selection. The first things to remember are exposure to sun, wind, and the type of watering (spray or drip) of the bed you are planting. Most plants that are labeled properly will give this information on its price tag. Once you have eliminated the choices that just won't work, take into consideration full growth size, compatibility to other plants, texture, and color.

So many clients tell me their beds are overgrown and boring. This problem does not happen if the size, texture and compatibility of the plants are considered before purchase. Also, if the exposure step is skipped, you are most likely to lose most of the plants in that area. Picking the right plants for the space is very important, especially in the Utah climate. Because of our soil, climate and even elevation, there is a thin line between what lives and what doesn’t live. Sadly, many of the plants we want in our yard just won’t survive.

The last step that will help you achieve healthy plants is the right balance in spacing. So many of us don’t have time to spend keeping the yard weed free that we think the best solution is to have smaller beds and more lawn. In reality that is self-defeating. If the beds are too narrow, the grass is able to infringe on the health of any plants in the beds and because nutrients and moisture are highly sought after but not easily found in our soils, the lawn can hinder the plants ability to thrive. Grass is even successful in competing with trees for their first five years of growth. And that of course is a major problem since trees tend to be the most important plant in our yard. We want the tree to grow in fast and give us shade and privacy and that is made very difficult by nearby grasses. In addition, narrow beds do not give root space for shrubs, ornamental grasses, perennials and annuals to get started and growing strong. Shrubs and trees especially need wide girth in the soil for their roots to stretch out and find nutrients, water and air. If the lawn already dominates the space, they constantly struggle.

For the beds themselves, here are several of the basic guidelines. Beds need to be at least 5 feet deep if you want to grow shrubs, 7 feet deep for trees, 3 feet deep for ornamental grasses or perennials. If you are mixing all of them aim for 6-8 feet deep as the smallest depth of the beds.

In conclusion, you will want to step back and create a strategy before attacking your landscape. Taking this extra time and energy in the beginning will save you enormous amounts of time and money as well as create a better product. The first step is to improve the soil structure with mixing in sand, compost, or topsoil as needed for your soil type. Next, try to avoid disturbing the soil. Then make sure to pick the right plant for the space, and create deep enough beds for the health of the plants you want. Using these guidelines will not only create a thriving landscape but lead to improved curb appeal and overall beauty of the space.

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