The demand, use and need of growing media worldwide is increasing due to the increased production of plants in containers and controlled environments. An industry that once primarily served the floriculture and ornamental nursery industries now serves a booming industry of container-grown vegetables, cannabis, herbs, leafy greens and small/soft fruit. The future is very promising and strong for the continued need of various growing media components as more and more countries become more advanced in growing crops in containers, and as more and more different (both new and traditional) crops around the world begin to be cultivated in places other than the field.

With increased demand and use comes increased interest by some to recycle or reuse their growing media, otherwise it has to be disposed of in some way. A practice that is as old as our current green industry, the reuse or repurposing of growing media has been met with rewards as well as some serious challenges by different individuals. While searching the scientific literature, trade magazines and online sources, I began to quickly realize the scope of what is known, not known or believed regarding the pros and cons of reusing growing media. The following terms occurred multiple times as I searched this topic: reduce, reuse, recycle, reutilize, rehabilitate, reclaim, repurpose, restore, regrind, recondition, replace, reduce, reprocess, repeated, reapplied. I never knew there were so many synonyms for reuse! With this being stated, let’s take a quick look at some of the various pros and cons of reusing organic growing media. The reuse of inorganic materials (rock/mineral wools, perlite, pumice, clay pebbles, etc.) deserves a separate and more thorough discussion of their own as they have potentials, reuses and issues much different than the organic materials.

First, some terminology. Often, nomenclature can often be confusing, and words or concepts are used interchangeably when they should not be.

• Sterilization — the temporary destruction of most all living organisms including microorganisms, bacteria, fungi/spores, nematodes, insect eggs, weed seeds, etc. using heat of at least 212 °F for at least 30 minutes.
• Sterile — free from most harmful pests or diseases commonly problematic for cultivated plants. Can be achieved without steaming/heating and does not eliminate all microorganisms/biology in the soil/substrate.
• Sanitation — a condition, situation or environment that is free of harmful pests.
• Solarization — the use of the sun’s energy to heat soil/growing media that is covered in a transparent polyethylene tarp and allowed to heat to at least 160 °F. This can be for a short time, 30 minutes, or over the course of weeks, depending on the setup and operation.
• Pasteurization — a process of making something free from most forms of bacteria, microorganisms, diseases, weed seeds or other forms of life. This is typically achieved with steaming to a temperature of about 180 °F for 30 minutes.

Growing media can be essentially sterile without being sterilized or pasteurized. Peat moss for example, contains many natural beneficial microorganisms, therefore not technically sterile, but it typically contains none that are harmful to plants grown in the moss. Sterilizing peat moss would destroy the beneficial organisms, thereby reducing the quality of the peat. Also, by virtue of where peat originates, it is not prone to have weed seeds or contain insect eggs/larvae, or other potential pests that would harm horticultural crops. The same can be said of many of the commercialized wood fiber products currently on the market.

Many growers may not have the need to dispose of or recycle growing media if all their crops are container-grown and shipped out or sold. An exception may be the need to dispose of unsold, damaged or poor-quality plants that often get piled outside somewhere on the property. These “death piles” can be seen at many nurseries and greenhouse grower operations across the country.

It is also important to note that even if recycled growing media (or soils) are sterilized to remove all potential pests, it does not mean that the materials will remain sterilized. Sterilization of any material is only a temporary state or condition. If pests or diseases are present in the potting or production area, they will be re-inoculated quickly.

Potential risks

Recycled growing media can have some detrimental properties that should be considered and monitored. First is the potential loss of physical properties of reused media. Over time, organic particles naturally break down (decompose), thereby decreasing structure and air porosity. If materials are ground up or otherwise handled during sterilization processes, the particle size will continue to reduce, therefore changing the physical properties when repotted. Blending in some percentage of new growing media with the old/reused would likely help with this problem.

Secondly, reused growing media can house potentially harmful pathogens, pests and other unwanted goodies if not properly sterilized or treated. The infection or exposure that improperly recycled materials can have on a grower operation can be very detrimental to future crops and cropping cycles. Recycled materials left outdoors can easily be contaminated with weed seeds and or pathogens. Recycled materials not properly sterilized could contain Pythium, Fusarium, Phytophthora and other plant-sensitive diseases. The recent increase in legalized cannabis production has also exposed new biological concerns (many may be unfounded) including the presence of E. coli and Salmonella in growing media that are now being monitored and, in some cases, regulated for.

Lastly, there can be some toxicity effects from reused growing media. Mostly in the form of residual fertilizer salts that can create high EC in mixes when re-blended or reused in future crop productions. This can alter fertility practices and management as well as crop growth response and control. Desalinization via washing or flushing with hot water is needed to remove potential salts from materials like coco coir.

Potential rewards

If done properly and monitored, the reuse and recycling of growing media can save money for some growers if they are willing to invest the time and resources to properly do it. Growing media is often not cheap, so it is possible to save some money. Reuse of materials is also a great way to reduce the disposal of organic and inorganic materials and make operations more sustainable and carbon-neutral. Some cut flower growers and others have the process of recycling their growing media down to a science and have been very successful for many years incorporating it into their growing systems.

Your growing media is such a vital part of the success of your production system, be that large or small, professional or hobby market. If you reuse or recycle, do it right and understand the potential consequences. Cutting corners or trying to save a dollar may be worth it on some things, but do not jeopardize the quality and performance of your growing media. Your plants will thank you.

The author is an associate professor and director of the Horticultural Substrates Laboratory at North Carolina State University. He can be reached at Brian_Jackson@ncsu.edu

At the end of January, I was saddened to learn that the Southern Nursery Association (SNA) board of directors voted unanimously to shutter the organization. Because of the continued strain on travel from the coronavirus, SNA was unable to host its 2021 conference, its main source of income.

Founded in 1899, SNA’s mission was “to unite and advance the horticulture industry through educational, research and marketing efforts.”

SNA produced a robust trade show from 1950 – 2009, the SNA Research Conference from 1955 to 2020, and the SNA Plant Conference from 1991 to 2020. The association also produced The Best Management Practices Guide in 1996 with updates in 2007 and 2013.

Some of the research that came out of the SNA Research Conference was groundbreaking, and thankfully the library of more than 3,000 titles will eventually be housed on the Horticultural Research Institute (HRI) website (www.hriresearch.org).

SNA Executive Vice President Karen Summers says the board is exploring other avenues with AmericanHort to help preserve the research conference, the student competition, and the BMP Guide.

To help preserve SNA’s 121-year legacy, two existing HRI funds (the SNA Fund and the SNA Golf Classic Fund) will be combined — totaling some $300,000 — and renamed the Southern Nursery Association Legacy Fund. These funds are earmarked for horticultural research in the southeast region of the U.S.

The organization’s impact on horticulture students is immense. And I was relieved to hear that the Sidney B. Meadows Scholarship Endowment Fund (www.sbmsef.org) will not be impacted. It’s a non-profit 501(c)(3) charitable corporation fully independent of SNA and will continue to award academic scholarships to horticulture students throughout the southeastern U.S. To date, the fund has awarded more than $550,000 in scholarships. The fund balance currently stands at more than $900,000.

I’d like to tip my hat to Karen and Danny Summers, who have worked tirelessly to promote and expand SNA. I know this was a heartbreaking decision for them and the board.

When an organization like SNA has been around for more than a century, its closure will have a ripple effect on the industry. We must not take things like research and scholarships for granted. Our local, state, regional and national organizations need our support to maintain the assistance and benefits they provide the industry. In this new and likely unconventional year, consider volunteering your time and becoming a dues-paying member to a nearby association. Let’s keep the legacy of SNA alive.

I recently watched the movie “Fletch” for the umpteenth time. One of the things that makes me laugh is all the aliases Irwin Fletcher invented during the course of his undercover investigation. Saxifraga stolonifera has an impressive array of pseudonyms as well, from strawberry geranium and strawberry begonia — it is neither a begonia or a geranium — to creeping rockfoil and roving sailor, and a few more. Whatever you want to call it, Saxifraga stolonifera is a fabulous garden plant for light to moderate shade. As its name implies, it spreads by creeping stolons much like a strawberry and its leaves are shaped similar to a geranium or begonia. It’s easy to see why gardeners have called it strawberry geranium or strawberry begonia. It forms a dense groundcover and sports showy white flowers on 18-inch stems from late spring through mid-summer. The foliage is evergreen, and quite eye-catching. The undersides of the leaves are a dark pink-red color and add to the plants allure. There are a few notable varieties available in horticulture. ‘Hsitou Silver’ collected from the Hsitou region of Taiwan has beautiful silvery foliage, and there is a nice, variegated form marketed as ‘Tricolor’.

Saxifraga stolonifera is native to China, Taiwan, Japan and the Korean peninsula. It grows in humus rich, well-drained soils in partial to full shade. It received the prestigious Award of Garden Merit from the Royal Horticultural Society. S. stolonifera is a great shade groundcover in the landscape and is also a fabulous container plant. It’s relatively easy to grow in nursery production, as well as in the garden. Damage from disease or insects is rare. You won’t regret adding Saxifraga stolonifera to your production plan or to your garden.

Although the box tree moth (Cydalima perspectalis) has not yet arrived in the U.S., the pest is not far away. The pest is native to eastern Asia, and was detected in Toronto, Canada, in 2018 and is prevalent throughout Europe.

Based on DNA evidence, box tree moths were introduced into Europe from Asia multiple times and moved within Europe via nursery trade after they were introduced. Once the moths got onto wild European boxwoods, they were able to spread relatively unchecked.