Kenaf Core as a Container Media Component for Woody Landscape Plants and Greenhouse Bedding Plants

The selection of media components to successfully produce plants in containers is based upon freedom from soil pests and harmful chemicals, cost, shipping weight, availability, water­holding capacity, cation exchange capacity, and pH. Current organic and inorganic materials used to formulate container plant growth media include pine bark, peat moss, composted rice hulls, sawdust, mushroom compost, sand, vermiculite, and perlite (Bunt, 1984; Nelson, 1991; Whitcomb, 1984).

Studies were conducted at the South Mississippi Branch Experiment Station and at Mississippi State University to evaluate the potential use of kenaf fiber core as a substitute for pine bark for producing woody landscape plants and as a substitute for vermiculite in peat moss­based plant growth media for growing bedding plants.

Excellent growth of Ilex 'Cherokee' and azalea 'Wakaebisu' was obtained when kenaf fiber core was used as an organic component of container media. Growth of plants in media containing kenaf, especially with composted kenaf, compared very favorably with the growth of plants in pine bark, the most commonly used organic component to grow woody landscape plants in containers.

Results after only one growing season indicate that composting kenaf is beneficial for plant growth and will produce a more stable media. Plants grown in composted kenaf were slightly larger, weighed more, and had better root systems than plants grown in kenaf not composted. Plants grown in composted kenaf were similar in size and weight compared to plants grown in pine bark. Better root systems were obtained with pine bark compared to composted kenaf, however. Poorest root systems were obtained with the kenaf medium that was not composted. Growth of plants of azalea 'Wakaebisu' grown in pine bark, kenaf that was not composted, and kenaf that was composted were only slightly different in height, width, fresh weight, and root ratings.

Crops that are grown over one or more years to produce marketable plants require the use of organic components that are relatively stable and do not decompose at an excessive rate. Composting kenaf for periods of time longer than 3 months, as was used in this study, is needed to further explore composting as a possible method to improve the stability of kenaf fiber core.

Preliminary results using kenaf fiber core of several particle sizes, with and without short­term composting, at four dolomitic limestone rates and two rates of complete fertilizers, indicate that kenaf fiber core can be used as a growth medium component to produce woody landscape plants in containers.

Additional nutrition and composting studies with kenaf fiber core are needed on a wide assortment of varieties of woody ornamental plants to determine the reliability of this material or use in growth media for the nursery industry.

Plugs of Celosia argentea (celosia), Viola x wittrockiana (pansy), and Impatiens wallerana (impatiens) were transplanted into 10­cm pots containing five different peat moss­based media modified with fiber core of kenaf and/or vermiculite. The maximum height, width, shoot weight, and root weight for allthree bedding plant species were found in the media containing no kenaf. The pH increased linearly as the proportion of kenaf increased in the media.

Freshly milled fiber core of kenaf will not replace vermiculite in peatlite medium. Plants were stunted and cholortic, indicating traditional nitrogen deprivation in spite of the fertility regime. In its raw form, kenaf fiber core apparently does not have a satisfactory carbon:nitrogen ratio for plant growth; therefore, prior to its use as an amendment, it must be composted.

Literature Cited