ASHS Press Releases

American Society for Horticultural Science

  • Increase font size
  • Default font size
  • Decrease font size
Home HortScience Organic Amendment Grows Robust Tomato Transplants
E-mail Print

EAST LANSING MI—The increase in organic acreage is creating a new demand for organically grown vegetable transplants. Commercially available certified vegetable transplants and organic mixes for transplant production are limited and usually expensive, challenging organic growers to produce transplants and design their own mixes on-farm. Recent research from Michigan State University's Department of Horticulture provides organic growers with economical, effective solutions for producing healthy tomato transplants.

Scientists Ajay Nair, Mathieu Ngouajio, and John Biernbaum tested the use of a peat-compost based growing mix supplemented with an alfalfa-based organic amendment. The team was looking for ways to develop an efficient transplant production protocol by determining optimal concentrations of an alfalfa-based organic amendment. "We also wanted to ascertain the optimal incubation time of the medium with the amendment to ensure timely supply of nutrients and avoid seed or seedling injury," said lead author Ngouajio. The full report appeared in HortScience.

The researchers used 25 growing medium treatments of an organic amendment derived from alfalfa, meat meal, molasses, and sulfate of potash. The compost, produced at the Michigan State University Student Organic Farm, was composed of straw and wood shavings from livestock bedding, leaf mold, and straw and hay formulated to produce a high-carbon, low-nitrogen mix. A growing medium composed of peat, vermiculite, and compost was amended with 0%, 0.6%, 1.2%, 1.8%, or 2.4% by weight of the alfalfa-based mix and incubated for 0, 1, 2, 3, or 4 weeks.  Tomato seeds germinated in each treatment were measured for a range of growth characteristics.

According to the report, seeds grown in peat-compost without any amendments had the highest germination rates; however, severe nutrient deficiency suppressed seedling growth. Compared to plants grown in medium with no amendments, tomatoes grown in the amended medium showed increased stem diameter, height, leaf chlorophyll content, and plant dry weight (90% to 160% more), provided the amended medium was incubated for at least one week. "There are benefits to incorporation of alfalfa-based amendments in compost-based medium when compost alone (at 25% volume) was not able to provide sufficient nutrition for the desired transplant growth," said Ngouajio.

The results showed that growing medium amended with 0.6%, 1.2%, 1.8%, or 2.4% concentration of alfalfa-based amendment produced transplants with "suitable growth characteristics" and met commercially acceptable standards for transplanting and handling. A higher rate (2.4%) of amendment produced robust and healthy transplants but had the potential to affect seed germination.

"The use of plant- and animal-based amendments, together with compost, has the potential to serve as nutrition supplements for sustainable greenhouse transplant production," Ngouajio concluded. "From a grower's standpoint, the adoption of any production system or technique is often driven by cost of production. This study showed that use of the alfalfa-based amendment is economically feasible and would benefit organic growers if approved by the Organic Materials Review Institute (OMRI)."


The complete study and abstract are available on the ASHS HortScience electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Alfalfa-based Organic Amendment in Peat-compost Growing Medium for Organic Tomato Transplant Production
Ajay Nair, Mathieu Ngouajio, and John Biernbaum
HortScience 46:253–259. [Abstract] [Full Text] [PDF]

Corresponding author. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it