How Does Coffee Help Lima Beans Grow?

Composting with Coffee

• Coffee grounds are a source of waste in many kitchens, so they can go into a compost bin. They provide significant nitrogen levels that are ideal for composting. Oregon State University Extension Service recommends layering one-third each of leaves, grass clippings and coffee grounds in a compost pile. Since pH levels in coffee grounds are likely to change as they decompose, you probably can't use them to control the pH in the soil for lima beans, which do best in a soil pH of 6.5.

As Soil Additive

• Coffee grounds can be added directly into the soil to improve soil structure for lima bean plants, or added in a layer on top of the soil and covered with mulch. Anecdotal evidence suggests that the coffee grounds may kill or repel slugs and snails, according to Washington State University. Coffee grounds also encourage the growth of beneficial microorganisms in the soil. When adding them directly to soil, include a nitrogen fertilizer to help these microorganisms to grow.

How it Works

• Some types of bacteria and fungi may work to break down coffee grounds when the grounds are added to compost or soil, and could ward off certain harmful fungi. In research cited by Washington State University, coffee grounds helped control fungi and diseases in beans and other crops under controlled conditions, though the experiment was not replicated in a natural garden setting. Coffee grounds also act as a food source for earthworms and could improve soil structure by attracting them. Another benefit of coffee grounds is in the production of humic substances. Humic substances are the essential, biochemically active components of soil required for most plants to grow, and they are created as coffee grounds break down.

Lima Bean Growth

• Lima beans prefer well-drained, highly organic loam soil. Coffee grounds, along with fertilizer and other soil additives, can provide this. As warm season crops, lima beans need lots of sun and moisture. Consistent moisture ensures a vigorous crop and coffee grounds can be used as a mulch to help retain soil moisture. According to Washington State University, studies have shown that coffee grounds applied as mulch and soil additives improve the growth and yield of cabbage and soybeans. Other plants did not see these benefits, so further scientific research would be needed to determine the growth benefits on lima beans specifically.