By Guy Holmes

Of all the potential energy a serious gardener can expend to understand plant needs, soil testing sits at the top of the list for return on your investment. However, there are components of this process that need to be understood to ensure the results aren’t wasted or misinterpreted, running the risk of damaging your gardening success. The concept of soil analysis is quite basic at its core: using a standardized, industry- recognized methodology of laboratory practices to reveal the type and quantity of plant nutrition present in the soil environment. Further and complementary analysis can be done for additional media characteristics—such as pH or porosity, which can reveal other factors related to plant health and nutrient uptake, like drainage potential (from which we can infer available oxygen levels essential for aerobic nutrient breakdown).

Analysis can identify poor physical qualities of a soil or potential nutritional excesses or deficiencies, but, perhaps most importantly, it can identify which form of supplementation you’re missing. Armed with this knowledge, you have the potential to seriously boost your yield. This may seem somewhat obvious, but it’s no small feat to “peer” into the material that surrounds a plant’s roots system and mind the important considerations:

• The physical nature and components of that root zone material.

• How and when those elements play a role in the support of a plant’s nutritional needs.

• Which nutritional needs are specific to your growing conditions?


A sample is collected of the “soil” in question, and sent off to a laboratory, where it’s analyzed physically and chemically with specialized equipment. Lab technicians follow international standards with established protocols for this type of quantification, and then verify and compile the results of the tests. Some labs interpret and offer advice based on the results and some do not, so ask ahead to see if consultation comes with the analysis.


There are multiple options for soil analysis: your local college extension center, a university, or working directly with your soil or fertility producer to assure you’re using those products to their full potential. In a more traditional agricultural setting, it’s quite common to have agronomists to collect soil samples, run analysis, and make recommendations of inputs and practices to improve yield and quality.

In the cannabis industry, your options are a bit slimmer. You can hire a qualified consultant, work with a third-party lab, or work directly with your supplier (if they have the lab facilities). These options have the best likelihood of giving you direction, provided that the scientists in question understand cannabis fertility needs. When it comes to cannabis, the fertility needs and nature of the finished harvested material are quite different from your average crop. There are not many fast-growing annual plants harvested for the dried weight of their intentional seedless flowers.

Lack of credible data on cannabis nutrition is a major problem and one that needs to be at the forefront when you choose a consultant or partner. For many obvious and some obscure ones, good data on the exact requirements of cannabis is hard to come by. The myriad of extremely different cultural practices for cultivating cannabis makes it even harder to then translate any data collected into good advice grounded in experience in that cultivation style.

For example, cannabis has very different needs when gown indoors under artificial light versus full sun outside. Fortunately, finding and interpreting credible data gets easier as time and legislation march forward and we narrow practices to a few dominant cultivation styles. A number of private companies have put quite a bit of research into cannabis nutrition and the necessary properties required for the soil in which it grows, but it can be difficult to discern the real experts from the companies that are primarily investing in flashy marketing. So take the time to seek out reputable producers who have real information and make sure to follow that old adage: “If it sounds too good to be true, it probably is.”

Owing to the tremendous scope of traditional field soil agriculture, it’s easy to find a professional who is experienced in analyzing field soil. But there are some significant differences in the practice of analyzing field soil versus containerized medias. Soil from a hemp field is very different from organic potting soil and other cannabis grow mediums such as rockwool. Know your style and ask questions. If you’re growing in containers, you’ll want to find a lab that’s knowledgeable about container soil. If you’re growing organic, you’ll want to choose someone with that understanding. It’s also likely worth it to perform tissue analysis at the same time—this can be incredibly valuable support when trying to make fertility input decisions. In your search, consider finding a lab that can do both soil and tissue analysis, and ask questions to find a good match.

Clear communication is essential to leveraging the effort and expense of soil analysis into tangible results for your crop. Whether you have an urgent problem with a clear fertility excess or a general desire to review success of fertility practices, knowing the question will help the lab analyze and process your samples to get the right answers. You’ll also want to be clear about your grow conditions. Different strains, container sizes, fertility practices, watering, and solar variations can significantly affect the media you’re seeking to analyze. You’ll want to talk through the process with your consultant before you even begin to collect samples.


Once you get through the research and decide on a path and a partner, they’ll advise you on how to take a sample or may even send one of their staff to do it for you. To get meaningful results, the real key is consistency. This can mean multiple samples from the garden or even from a single container—by using averaging to remove the variation that’s inherent to this kind of testing, technicians can develop better data.

Although trial-and-error continues to be a fun and interesting aspect of gardening, there’s a special satisfaction in breaking down the science of your success and failures. This is how we learn and grow.