Boone County Purdue Extension, 1300 East 100 South, Lebanon, IN 46052 [email protected] 765-482-0750

The Great Eggplant Experiment and Cover Crops

A team of Boone County Master Gardeners working at the Lebanon Church of Christ Community Gardens decided to try an experiment in the eggplant raised garden.  Half of the bed was planted with ‘Black Beauty’ Eggplant starts.  This was their control group.  The other half of the bed, the experimental group, was planted with the same variety of eggplant and Crimson clover seeds were added at a later date.

Their results were astonishing!  The control groups plants grew about 2 feet high while the experimental group’s plants grew 3 feet high.  In addition, the experimental group overall’s harvest produced a higher yield in number and size of the eggplants.

Figure 1. Control Group Eggplant averaged 2 ft tall
Figure 2. Experimental Group Eggplant averaged 3 ft tall
Figure 3. Control group’s harvest in one day
Figure 4. Same day’s experimental group’s harvest – that day the number was the same but the bigger size.

Why did this work?  Clover belongs to a group of plants called legumes.  Peas, soybeans, alfalfa and peanuts are also examples of legumes.  Their roots contain visible nodules that house nitrogen-fixing Rhizobium bacteria.  Through a mutualistic relationship with the legume plant, these bacteria are able to take nitrogen from the air and convert it into ammonia and other plan-using nitrogen compounds, thus fertilizing the surrounding plants.  In other words, Master Gardeners added plant-fertilizer making factories!

Figure 5. Nodules with Rhizobium nitrogen-fixing bacteria

Crimson clover is a good choice as a cover crop as it will die back when the ground freezes, thus the plant will decompose adding nutrients to the soil before spring planting the next year.

On a side note, as your garden starts to wind down from the summer harvesting season, NOW (mid-September – October) is the time to plant a cover crop mix.  Such mixes usually include three different types of seed – Brassicas with taproots, legumes and grasses.  The taproot Brassicas include oilseed radishes and turnips.  Their deep roots create inroads between the soil clumps thus reducing soil compaction and allowing water to penetrate deeper into the soil.  Legumes will add nitrogen nutrients and grasses, such as cereal rye, prevent wind and water erosion of the bare soil and will become a green manure when tilled in.  This will add needed organic matter.   If planting a fall cover crop, a home gardener should look for a mixture that will die when the ground freezes, so decomposition occurs before the soil is tilled for spring planting.

Barb Burkhardt


Reece, Jane, Urry, Lisa, Cain, Michael, Wasserman, Steven, Minorsky, Peter and Jackson, Robert.   2011.  Legumes.  Campbell Biology, 9th Edition. San Francisco: Benjamin Cummings. p. 794-795.

Curt Emanuel. “Using Cover Crops in Home Gardens” August 20, 2020. Purdue University Extension presentation

Doug Higgins and Kristin Krokowski. “Using Cover Crops and Green Manures in the Home Vegetable Garden”, University of Wisconsin Garden Facts #XHT1209, UW Extension.