There is probably nothing that is cheaper or more effective at maximizing the lawn owner’s investment in their outdoor property than the lowly soil test. Almost every US state provides soil testing at minimal or no cost through a cooperative extension service. The proper use of the soil testing results very often saves the lawn owner from expensive purchases that may not be necessary, or can even be environmentally harmful. But year-after-year, these remarkably cheap services are ignored as lawn owners fall for the marketing that the “new, improved” products on TV this year will save them from last year’s failures, or last year’s regimen is followed blindly in the hope that the result will be different.
For the New or Casual lawn owner, there are two varieties of soil tests that should be considered. They are:
The Basic Soil Test: the basic test will provide the lawn owner with information about the pH of their soil, and the levels of Nitrogen, Phosphorus and Potassium. Most provide even more information than that. Costs range from free to about $5. Many cooperative extension services will also allow the lawn owner to call the service to discuss the results with a Master Gardener and hear their recommendations.
The Full Soil Test: the advanced test generally provides all of the above plus a significant number of other minerals and nutrients. This paints a picture for the lawn owner that (when discussed with a knowledgeable person at the cooperative extension or a forum like BESTLAWN.INFO) can lead to the best 1-3 year lawn care plan possible – all without spending money on unnecessary products.
To get a soil test, first locate the cooperative extension service online or by calling them and follow their directions. To actually get the soil for the test, you can use a simple inexpensive bulb planter. Simply push the bulb planter into the soil at least 4 inches, then pull it out. I use the soil between 3 inches and 4 inches deep (for flower and vegetable gardens, use the soil that is 6 inches down), and crumble it into a sandwich-size plastic bag. I repeat the process half a dozen times at random spots of the lawn, avoiding spots that may be used by pets for “biological needs”, and areas that may get winter de-icing salt. After I have 6 samples (about half a bag full), I shake the contents to mix the sample. Then I send it in for analysis.
You’ll get the results in a couple of weeks. Either call the cooperative extension service or post the results on BESTLAWN.INFO in the Soil Maintenance area and ask for an opinion of what to do. By all means, tell the person that works with you what your grass type is, and what you have as your goal. It’s that simple!
Soil Structure Test
There are two tests that you will want to do topossibly help determine your soil structure. They are easy, and you can do them at home using only materials that you often can find in the recycling bin and the garage.
Rummage through the recycling bin, and find a clear, straight-sided plastic or glass container that will hold roughly a quart of water– I find that mayonnaise jars and fruit juice bottles work well. Fill it roughly halfway full of soil (no rocks, roots or grass) from the top four inches of soil that has been crumbled. Then fill the jar almost full with water. Cover it and then shake the contents until there are no more clumps of dirt. Set it on a flat surface and leave it there for two minutes, then mark the level of the settled soil. After two hours, mark the level of settled soil again. Leave it for two days, then mark it one final time. Now look at the jar without stirring it up. The lowest mark is the tiny pebbles and then the sand in your soil. Next to settle is the silt, which is the second mark - the middle-sized particles of your soil. The last items to settle are the clay particles, and are the items between the second mark and the third mark. Anything that floats or gently sits on top of the clay is organic material that hasn’t decomposed yet.
So now you have a pretty good estimate of how much of your soil is made up of the major soil structure components. While you can’t use this test to accurately estimate the organic content of the soil, the rest is a pretty good test. Here’s a little information at the sand, silt and clay components:
Sand is the largest particle in your soil and typically settles out of the water in the jar in a few seconds. Sand has lots of spaces between the individual grains, and water poured into sandy soil drains away very quickly. Because your lawn can only take in nutrients that are in water, the grass doesn’t have much time to get its nutrition before the water is gone. In a strange twist, it also is the type of soil that requires the most fertilizer, since it doesn’t hold the nutrients well and the water that moves through it dissolves any nutrients down into the subsoil trough a process called leaching.
Silt is the medium-sized material in the soil. If you had a bunch of it by itself, it feels like chocolate powder or flour. It is, for the most part, rocks that have been worn down by nature to a pretty small size. River deltas are primarily silt, and make a beautiful soil that is often easy to work with.
Clay is the tiniest particle that makes up soil. Because there is so little space between clay particles, water tends to stay in or above the clay for a long time. Ironically, though, even though water and nutrients stay in clay a long time, lawns and other plants don’t tend to do well in clay because air cannot get into the soil, and the plants and good soil microbes need oxygen to do their work.
In some cases, there may be settling of the soil below the line(s) that you have drawn. If this happens, it disqualifies the test from being interpreted.
So, what does all that mean and which one do you have?
Well, in reality, you probably have a mixture of all three, unless you live in the desert or in the middle of the Mississippi Delta. Most typically-good soils center around the “Loam” category in the graph to the right. “Perfect Loam” is roughly 40% silt, 40% sand and 20% clay. It holds some water and nutrients, drains well, allows air penetration, and doesn’t compact very easily. If you have a loam soil, keep the organic material at a reasonably high level, replace the minerals and nutrients that leach out of the soil and be happy. If you don’t have a loam soil and want to grow a perfect lawn, you may have to decide whether you want to amend the soil, which may require that you read, understand and practice the techniques in the more advanced articles in this series.
Soil Percolation Test
The second soil structure test is a percolation test. This test allows you to understand how rainfall and irrigation water moves through your soil. All you will need for this test is a garden shovel, a water hose and a ruler.
Find a typical spot in your lawn where you can dig a hole that is 1 foot long, 1 foot wide and 1 foot deep. As carefully as you can, remove the sod from this spot and place the sod out of the sun. Now slowly dig downward through the topsoil. If you hit the subsoil before you reach 1 foot down, put the topsoil and the subsoil in different piles. The hole should be roughly square – not smaller at the bottom than the top.
Now, fill the hole to the top with the garden hose and note the time. The level of the water should steadily fall at a little less than 2 inches an hour. Compare your results with the below:
Level goes down more than 2 inches an hour – your soil drains too quickly, and you may have trouble keeping it moist and fertile
Level goes down less than 1 inches an hour – your soil drains too slowly, and often indicates high levels of clay and/or soil compaction
Level goes down 1-1/2 to 2 inches an hour – your soil drains well
Soil drains well at first, but then slows dramatically – you may have a high level of clay in the subsoil that prevents the topsoil from draining after it becomes saturated
Compare your findings from the first test with your results from the second test. If you have a soil with high levels of clay, the percolation test should confirm it with slower drainage results. A soil with high levels of sand should drain quickly. Ask for help in the BESTLAWN.INFO Soil Management Forum if the test results do not confirm each other.
If you have soil that drains very quickly, then the “deep, infrequent” watering techniques that are promoted in this article series and online at BESTLAWN.INFO may not work for you (or may need to be adjusted), unless the soil is amended to hold water better.
The soil pH is an indicator of the acidity/alkalinity of your soil. Most grasses do well between 6.5 – 6.8 pH, although some do well outside that range. A value of 7.0 is neutral – neither acidic nor alkaline. Values lower than 7.0 are acidic, and values above 7.0 are alkaline. The soil’s pH is very important – many nutrients become unavailable or less-available as the pH becomes very acidic or very alkaline.
Do not be surprised if your pH is well outside of the range this article indicates. Parts of the US and Canada can easily go below 5.0 or above 8.0. This can be corrected over time in more than 90% of the cases that we see. If the soil supports grass now, then the soil can only improve if the effort is made. In most cases, Lime will move the ph upward and Sulfur products will move it downward. Lawns regularly treated with larger quantities of composted organic matter have a tendency to move toward a neutral pH when compared with surrounding lawns that lack organic matter.
Important Soil Components
You have no doubt heard that all lawns require nitrogen (N), phosphorous (P) and Potassium (K) to grow well. While this is true, it is only a partial picture. As there are several other essential items that are necessary and/or affect the ability of the lawn to use those nutrients. The pH of the lawn soil can also dramatically affect the ability of the lawn to use nutrients.
The (Old) Big Three - NPK
Nitrogen (N) is the primary material needed to grow plants, including grasses. It is always the first number in the NPK analysis of a nutrient source. Nitrogen is a component of the Chlorophyll that plants need to stay alive and provide themselves with food. But Nitrogen use is heavily dependent upon the type of grass being grown. Some fescues don’t want any more than 0.5 lbs per 1000 square feet of Nitrogen annually – indeed they do poorly in a Nitrogen-rich environment. Some types of Kentucky Bluegrass demand 3-4 lbs of Nitrogen per 1000 square feet per year. So, it is very important to know what type of grass you are growing before you decide how much of it you will need to supply, and when to apply it. Nitrogen does not remain in the soil for very long however, so it must be supplied periodically. It can be supplied organically through several natural sources, and is available in fast-release and slow-release commercial products.
Phosphorus (P) is necessary to lawns, and is essential to root formation, turf density, drought tolerance and winter hardiness. Phosphorus is always the second number in the NPK of any product sold. In most loamy and clay soils, Phosphorus does not leach easily, but it can be a problem if it gets into water supplies, ponds, rivers and lakes. Because of this, many US states have taken action to mandate “no phosphorus” fertilizers. Lawns should always be tested for Phosphorus levels before additional Phosphorus is added, as it has become an almost casual addition to lawns when Nitrogen is added. New evidence is showing that lawns require significantly less supplemental Phosphorus than was originally thought.
Potassium (K) is also required for lawns. It is always the third number in the NPK analysis of a nutrient source. Like Phosphorus, Potassium does not leach easily from most soils and is held long-term in all soils except for sandy soils (it leaches easily from sand-based soils for reasons beyond the scope of this article). Potassium works in the lawn to build chlorophyll, promote protein and carbohydrate production, water regulation, drought tolerance, winter hardiness, improved resistance to certain fungal diseases, and greater tolerance to insect damage. Lawns should always be tested for Potassium levels before additional Potassium is added, as it has become an almost casual addition to lawns when Nitrogen is added. For sandy soils, Potassium should be more closely monitored.
The Other Essentials (Movin’ On Up)
Not long ago, most people followed a regimen of “it’s time to put some fertilizer on the lawn”. They saw that the lawn was declining (probably due to the leaching of Nitrogen) and added whatever was on sale for a good price at their local store, regardless of the Phosphorus and Potassium that was being added to the soil. After all, it worked – the grass got healthier-looking quickly. Over time, the soil built of large reserves of Phosphorus and Potassium, some of which leached to the water table, or ran off into surface waters, polluting the waterways and causing algal blooms in them. Recently there has been more information and a plethora of cheaper soil testing available, and the additional research has led to a more measured approach to the addition of nutrients to the soil. The additional research also has indicated that there are many interactions in the soil between nutrient and environmental considerations, and several other minerals are needed for the soil and the beneficial soil microbes that are present. They are:
Calcium (Ca) – In the author’s opinion, Calcium is the second most important item (behind Nitrogen) for a healthy, balanced lawn. Phosphorus and Potassium are important, but except in certain conditions can almost be taken for granted - especially if the lawn clipping are mulched back into the lawn. That may be heresy to people brought up on the importance of the NPK, but I have never seen a healthy soil that had a Calcium deficiency. Calcium helps the availability of major plant nutrients. It also acts as a regulator for some elements like zinc, copper, and especially phosphorus. It promotes bacterial activity and makes favorable soil structure and relationships. The soil becomes more porous, improving air circulation and the ability of the soil to absorb and hold moisture.
The problem is that Calcium is slow to react to the soil (unlike Nitrogen), so one of two scenarios often gets played out: (1) the lawn owner doesn’t bother to take care of Calcium since it will take many months to affect the soil, or (2) the lawn owner adds excessive amounts of Calcium and Magnesium to the soil looking for a quicker response. The right way to adjust Calcium is to get it to optimal levels over time, while monitoring the pH and calcium/magnesium ratio through inexpensive soil testing (Calcium should be near 7:1 with the level of magnesium in the soil). The best sources of Calcium are Calcitic Lime (which is used where the soil doesn’t require magnesium) or Dolomitic Lime (where the soil requires both calcium and magnesium).
Iron (Fe) – while Iron plays a central role in animals (blood is completely dependent upon Iron), in plants its role is smaller but still important. Iron is important to the processes behind Chlorophyll, and a deficiency will cause Chlorosis (yellowing of leaves). Iron’s availability in the soil, however, is dependent upon the pH of the soil and it should not be assumed that Iron is physically deficient without a confirming soil test. There are both organic and commercial solutions available to aid in the proper maintenance of Iron.
Magnesium (Mg) – magnesium is the good cop/bad cop of the essential minerals. If there are optimal amounts of it and it is in proportion to the calcium, it will darken the lawn and promote many healthy processes both in the plant and the soil. Excessive magnesium, however, causes diminished drainage capabilities of the soil, a form of hardening of the soil, and an increased presence of certain weeds in the lawn. Excessive magnesium often comes from the use of dolomitic lime when the homeowner applies lime to either raise the soil pH or to add calcium. It can also occur from using Epsom Salts or de-icing products that contain Magnesium Chloride.
Micronutrients are beyond the scope of this article, which is for the new or casual lawn owner. Micronutrients should only be added if the person assisting you to interpret the soil tests you receive says they are critically deficient.
(c) 2009 Andy Hejnas - All rights reserved
BESTLAWN.INFO Soil Management & Composting Moderator