Heather Kirk-Ballard, Kathryn Fontenot and Edward Bush

According to the 2022 Garden Trends Report from Garden Media group, home gardeners have a renewed interest in edible gardening with the highest growth in seed starting and container grown vegetables. The new gardener of today is interested in growing their own food in a sustainable way, and with shrinking lot sizes and larger home footprints, our urban gardeners are making use of less space. Home gardeners living in smaller areas do not have easy means of vegetable production. One solution for achieving optimal vegetable yields is by using a modified growing medium in container production of vegetables. The objective of this study was to determine if the Garden Greaux media developed by LSU AgCenter is a suitable medium for container production of certain fruits and vegetables compared to the control and industry standard mix.

In this study, three container mixes were evaluated for their use in the production of cucumbers, tomatoes and sweet potatoes. Those mixes were Old Castle topsoil, which served as the control, PRO-MIX as the industry standard and a potting soil developed by LSU known as Garden Greaux. All plants received irrigation daily to maintain substrate field capacity, which is the maximum amount of water a medium can hold. For the cucumbers and tomatoes, both the count and total harvested weight were doubled in the LSU substrate mix as compared to both PRO-MIX and Old Castle yields. The sweet potato count and total weight or yields were also greater when grown in the LSU potting soil. The sweet potato totals were three times the count and eight times the weight compared to PRO-MIX soil and greater than four times the count with eight times the weight when grown in Old Castle. In conclusion, the LSU packaged substrate outperformed the other two mixes and produced acceptable fruit quality.

Materials and Methods

This experiment was conducted at the LSU AgCenter Hill Farm in Baton Rouge, Louisiana, on a nursery yard that simulated a homeowner’s patio. The 7.5-gallon black plastic nursery containers were arranged in a randomized block design with drip irrigation which used Baton Rouge municipal water delivered by spray stakes. Each medium treatment and crop combination was replicated 10 times, and each planting was replicated over two planting dates, one year apart. The three media treatments used in this study were Garden Greaux, produced by Phillips Bark, Brookhaven, Mississippi; a commercially available bagged PRO-MIX, from Premier Tech Horticulture, Quakertown, Pennsylvania; and Old Castle topsoil, a Timberline product. The base mix of the Garden Greaux media treatment in the study was 80% pine bark and 20% peat moss with incorporated slow-release fertilizer and lime to adjust pH and micronutrients. The combination of moss and bark provides good medium aeration, water holding capacity and cation exchange capacity.

The media treatments were evaluated to compare fruit and vegetable production of Dasher II cucumber, Sweetheart of the Patio tomato and Jewel sweet potato. Once flowering in tomatoes and cucumbers occurred, a weekly application of Miracle-Gro LiquaFeed All Purpose Plant Food Advanced (12-4-8) was applied for the duration of the study.

Pots were placed on 18-inch centers on the nursery yard and watered to saturate media before transplanting the vegetables. Transplants of cucumber and tomato crops were planted on May 1 in both 2020 and 2021 and harvesting began four weeks later. The study was terminated in August for both cucumbers and tomatoes when plants stopped producing. The sweet potatoes were planted on June 3 when slips were available and were harvested in September both years in 2020 and 2021.

Cucumbers and tomatoes were harvested once weekly. The number of fruits for each soil type was recorded along with harvest weights. Sweet potatoes were harvested upon completion of the study. The number of tuberous roots were recorded, and each was graded as either one, two, jumbo or culls. The individual weights also were recorded.

Results and Conclusions

LSU Garden Greaux outperformed the industry standard and topsoil control media treatments in all crops grown on the nursery yard. LSU branded soil is an excellent choice for vegetable production in containers for home gardeners. The combination of the mulch to moss ratio combined with micronutrients and lime offer a superior option for container substrates, and we recommend utilizing this mix for home vegetable production. The next steps will be to compare the LSU potting media with other commercially available mixes containing slow-release fertilizers.

Heather Kirk-Ballard is an assistant professor, and Kathryn Fontenot is an associate professor for LSU AgCenter Extension. Edward Bush is an extension professor with LSU AgCenter Extension.

(This article appears in the spring 2023 edition of Louisiana Agriculture.)

Graph 1. Average number count and average yield in pounds of Dasher II cucumbers harvested from container-grown plants with selected container mixes for two growing seasons.

Graph 3. Average number count of sweet potatoes and average weight in pounds of total harvested from container-grown plants with selected container mixes for 12 weeks over two growing seasons.

Graph 2. Average number count and average yield in grams of tomatoes harvested from container-grown plants with selected container mixes for 12 weeks and repeated over two growing seasons.