organic natural fields

Going organic with native soil fields

By John Cogdill, CLIA

Boulder City (CO) Parks has always been aware of the need to try and promote turfgrass vitality and keep fields safe for play, integrating everything from Sports Turf Manager Association safety checklists while applying the least amount of chemical intrusion possible (IPM).

We have been without the use of pesticides since early 2000. What follows seems relevant and speaks to the reasoning behind current methodology. In June 2011 Fox News published the following:

“Research conducted by the Centers for Disease Control and Prevention found the residue of numerous pesticides in the bodies of 15% of children tested, ages 3 to 7. What’s worse, the broken-down products used in organophosphate pesticides was detected in 98.7% of children studied. Some of the chemicals used in lawn “weed and feed” products, such as the herbicide 2, 4-D, can be very toxic even at low doses and may increase the risk of cancer, neurological and reproductive problems. When brought indoors on clothing, 2, 4-D can remain in carpets for up to a year.”

That being said, our organic approach has been sustainable and effective for our both our constituents and for our native soil fields. In early 2014 Ross Kurcab from Championship Sports Turf Systems analyzed and provided our foundational turf plan, which has worked well as we continue to evolve and expand both our product research and accepted BMP’s. Our organic program is typically slightly more expensive to operate than other more traditional programs, as synthetic fertilizer costs are typically less expensive than organic fertilizer. However, as we don’t pay for contracted pesticide and herbicide services the cost relationship might not be as dramatic as many might suppose.

Our organic programs also typically require a greater level of time investment as it relates to cultural programs, seed, topdressing etc. However, field use and hours of play are also at the forefront of this demand our quest for cost recovery. Our costs are not prohibitive, particularly as one realizes that our community places a very high value on the health/safety of our fields and that we take very seriously our responsibility to our constituents, in particular as it relates to pesticides and the level of public trust that we strive to maintain. It is also important to understand that our climate plays a large role in our ability to do this, and we are not faced with challenges such as a year round growing season and the humidity that much of the country endures.


Boulder soils are unique due to the amount of heavy clay, Bentonite and slowly disintegrating limestone deposits that exist. Soil testing has shown that we have nearly every type of soil and pH within range with heavy clay or clay loam being our primary structure. Our native soils have relatively large amounts of potassium that occur naturally for the most part.

Boulder soils hold Phosphorus well and we have been very aware and careful about adding additional P unless the soil test reflects this. We are concerned about excess P and the effects of runoff as well as potential leaching in soils that are of a sandy or sandy loam structure.

Boulder soils principal need is nitrogen and on our native fields we try to deliver between 3-5 lbs. of actual N per thousand. The typical field soil is below 5% organic matter in our area and the addition of organic compost and fertilizers help to support this need and provides increased soil tilth in nearly all instances.

We use various types of fertilizer injectors to apply liquid organic formulas; granular fertilizers applied by spreader and tractor is the norm for us. Compost is routinely applied to specific sites based upon soil test results and the level of use/play experienced.

Multiple applications of N in 1-1.5 lbs. per thousand usually beginning after the ground thaws in late March or early April and completing our fertilization programs in late September or very early October prior to any ground freezing and usually as the first frosts arrive. This schedule gives us the best in terms of soil temperature, which is necessary for optimum results when using organic fertilizers.

We conduct soil tests annually on our premier and satellite athletic fields and apply 3-5 times per year based upon individual field needs. Both OMRI certified and non-certified products are used.

One of the larger challenges that we face is that of former methods of construction in new field development from 10-20 years ago. Soil that had been brought in from other sites and sold as topsoil resulted in additional challenges as it combined with our heavy existing native soils. Typically, this material was just taken from a building or new development site, mechanically screened removing rocks and various other organic debris and spread over a new field site. This soil is basically devoid of any microbial life, low in organic percentage and was not adaptable to the existing subsoil. This in turn created drainage challenges and the greater need for additional organic matter.

Over the course of time the soil structure has been modified, largely through cultural methods and now supports an improved soil structure, which encourages plant growth. Another example and challenge for us is the amount of rock and basic pit run soils that currently exist and the corresponding challenge of managing their soil tilth. Our organic program has had a positive and noticeable effect on improving these challenges as well, particularly as it relates to water holding capacity. Cultural practices and compost along with other practices such as leaving the mow clippings have over the process of years modified these rocky and sandy type soils.

Cultural practices

Core aeration, topdressing, seeding and using our recycler dresser are all integral parts of our organic turf program. We have found that given a positive and proper environment with our fields, turfgrass for the most part will outcompete any weeds that we have. This may require more frequent mowing and increased fertilization based upon test results. But for the most part our fields remain looking good with very dense stands of grass, which take care of our primary field criteria concerns and alleviate the need for pesticide applications.

Select seed varieties are chosen from the top performing varieties out of recent NTEP trials. New seed polymer options are not used, and we do inquire as to whether the seed is neonicotinoid-free.

Current mowing practices at our athletic fields is to cut at 2-3 inches predicated on what sports are being played on them. Blades are sharpened often which in turn helps reduce leaf shatter and that potential for disease and has actually saved on our fuel consumption. Mowing frequency occurs anywhere from 1-4 times per week and is dictated by growth, never removing more than 1/3 of the leaf blade at any given time. We typically see on our premier field grass growth rate oat about ½ inch per day during optimal late spring early summer conditions. Once temperatures rise above 95 our bluegrass tends to not grow quite as fast.

Core aeration is done 1-5 times per year and more frequently as needed, based upon levels of compaction and field Clegg results. There is definitely a need for increased cultural practices with an organic program and the effects of completing this work or not, is always quite evident. Our typical practice is to core aerate, overseed and topdress with compost on native soils. We will core aerate goal areas and other high use areas as often as every 10 days during heavy play. These areas are then overseeded and drug, raked in or swept depending on the existing soil structure.

Native soil fields always have the cores left on them and are either drug after seeding and composting or left to dry and then mowed. Aeration holes are typically half inch to 5/8-inch circumference at 3-4 inches depth and 2 inches on center. Our recycle-dresser is typically set at 6 inches, again depending upon the soil structure followed by seed and a field drag. Depending on the existing turf density we will likely change direction and repeat in scarcely covered areas. What we have found consistently is that the scarce and weed infested areas are typically also the areas that will fail field hardness standards and will require additional efforts in order to be brought into compliance. Typical overseed rates are at or about 4-5 lbs. rye and 4-6 lbs. bluegrass. Premier fields are at about 5-7 lbs. applied per thousand.

Topdressing is a year round practice particularly at our high use and fields testing at low OM in order to improve soil tilth and provide the environment that is capable of out competing weed challenges. Topdressing typically follows heavy aeration and seeding and the compost product that we use is inspected by the Colorado Dept. of Agriculture. The compost is well aged, friable and free of large chunks, weed seed and excessive salt. We do not apply compost to sand-based fields.


Irrigation in the West and particularly in this area is of extreme importance in creating the appropriate environment for our organic program. Appropriate irrigation is critical to the organic turf program as either over or under watering creates issues of compaction and provides an environment where weed infestations can more easily thrive. As a matter of practice, irrigation audits are conducted on native soil athletic field sites and soil moisture bucket schedules performed as the audits are completed. The high end ETO requirement for Boulder in the summer of 2016 was 1.66 per week. The need for highly efficient systems providing appropriate coverage is critical and the end game goal is for our system particularly our rotors to be at .8 Distribution Uniformity. Systems are checked weekly and our central control system provides morning updates on high and low flow as well as, areas of catastrophic flow, which typically indicates a mainline break   We are currently in the process of converting fields from an ET base to one managed by soil moisture sensors all to better incorporate a system which speaks to organic health and vitality.

Whether it is fertilizer, pesticides or water any and everything can be used in a careless manner. Organic turf programs are always going to be scrutinized as they should be and thoroughly vetted to separate science from feeling or emotion. Our intent is to be objective by keeping good records, by soil testing, consistently in the field evaluating weed infestation, and demanding dense healthy safe fields for our patrons

Our work is examined from the point of science and what works in the field. Research is always a huge part of what we do and we are constantly looking for new and creative ways to make this work better for everyone.

John Cogdill, CLIA, is assistant operations manager, Boulder Parks & Recreation, Boulder, CO.