Organic Broadcaster

Plan now to grow healthy transplants for next season

By John Biernbaum, Michigan State University

This year I worked with a team of colleagues to start a teaching and incubator vegetable farm in Michigan’s Upper Peninsula. We developed an initial crop plan based on the Michigan State University (MSU) Student Organic Farm plan and the help of a neighboring farmer who was very generous with his crop variety information and planting schedule. This farmer grew transplants for our initial season. For next season, we plan to create a sweat chamber and germination room (and media storage) in the basement of one of the existing structures to use for the early transplants (February, March) and a heated polyethylene-walled room in our high tunnel as a finishing space for the short term. This planning process has been a good reminder of all the decisions that current and new farmers have to face when getting started. It also is a reminder of the importance of reviewing the farm transplant process each year.

Planning Basics

Transplant production is a series of questions and decisions, similar to or perhaps in miniature of the overall process of farming in the field. The questions don’t change much from year to year, but the answers change as the experience and maturity of the farmer and farm evolves. The end of the field season is a good time to start the review process and make written notes about any changes to be put in place at the start of the next transplant season. It can also be a part of putting together that seed order earlier so you get the varieties you want while the seed is available.

When I teach transplant workshops for farmers or the online organic transplant class through MSU, one of the activities I use is the development of a transplant action plan. Action plans are typically a method of providing the step-by-step actions necessary to implement the various goals of a business plan. Action plans can also be a method of keeping records and laying out farm or crop production plans that can be electronically modified and updated each year. There are three key parts to an action plan:

1. The tasks to be completed
2. The person responsible
3. A date for task completion

Composts for Transplants

Composts are an excellent media component for starting transplants. Keep in mind that composts can vary dramatically. What makes a compost good for transplant production? One factor is appropriate physical properties as characterized by texture (particle size), structure (aeration/water holding capacity) and uniformity. Screening for use in small cells is beneficial. The bulk density (weight per unit volume) is one measure of physical properties. Dry peat-based media weigh about 0.13 g/cc while soil weighs 1.3 g/cc. Composts are in between. Ours range from 0.3 to 0.9 g/cc, primarily dependent on how much soil is added.

A second factor is a balance between soluble and long-term nutrients. Electrical conductivity (EC) can be a simple measure of soluble nutrients. The saturated medium extract (SME) or greenhouse test is a recommended method of soil testing compost or root media for transplant production.

A third factor is the biology present in the compost. In addition to improving the growth of transplants, compost in transplant media can be a great way to move valuable long-term nutrients, organic matter and diverse biology uniformly into fields and intensive growing areas. A group of Cornell University researchers designed a research project to address the question of whether soil biology in transplants impacts plant roots during the season. The researchers grew tomato transplants in a variety of root media containing plant-based amendments, compost or vermicompost. Transplants were then established in the field and at regular (monthly) intervals the microorganisms in the root rhizosphere were compared. For some treatments, particularly vermicompost, the transplant media had a lasting effect on the microorganisms in the root rhizosphere for several months.

To further investigate the potential benefits of vermicompost, the Cornell researchers identified how vermicompost can protect plant roots from Pythium damping off and root rot organisms. The presence of vermicompost leads to the plant roots being protected from infection by Pythium by a coating of microorganisms. More details are available by watching this YouTube video:

Our standard transplant compost for 15 years has been:

2 bales of hay
1 bale of straw
1 bale (3 ft3 compressed) pine shavings
1 bale of garden-grade sphagnum peat (3 ft3 compressed)

This mixture will create a pallet-size pile that routinely heats to 150o F in three days if properly moistened (soak contents briefly to absorb 75-80 gallons water). A loam soil can be added at the start of composting to increase nutrient retention and wetting (1 or 2 5-gallon buckets). The mature compost can be used for transplant media, but at the Student Organic Farm, it is typically mixed with 25% peat and 25% vermiculite.

Over the years, we have learned that factors like hay quality (more nitrogen in the hay leads to more in the finished compost), maintaining the moisture during composting, preventing leaching of the compost pile by heavy rainfall (i.e. cover the piles after the hot phase), and the storage conditions for October through January while the compost is maturing (temperatures above 50oF) can influence the quality and soluble fertility of the compost.

When the price of hay went from $4 to $8 to $12 in the summer of 2012 due to dry weather conditions, there was motivation for alternative locally available feedstocks. For the past two summers as part of a graduate student research project, we have produced three mixtures (2:1, 1:1, 1:2) of aged tree leaves (previous fall) and fresh clipped (flail mower) and raked “hay” from grassy unplanted areas at the Student Organic Farm. Other composts include adding peat, paper, pine shavings and manure to the 1:1 leaf/grass mixture or wrapping the leaf/grass mixture in plastic film to reduce oxygen and maintain moisture. The variety of C:N ratio finished composts will be used to grow vegetable transplants next spring.

Worm or vermicompost as a root medium component or a supplemental source of nutrients has been a transplant production option for several decades. However the limited availability (primarily dairy manure-based products) and higher cost of vermicompost compared to thermophilic compost has limited use for small-scale transplant production. Much of the previous plant growing research using vermicompost has been with large-scale production from dairy manure-based feedstocks.

Both thermophilic and vermicomposting of dairy manure will result in nutrient-rich composts that can be added to root media at only 10 to 20% by volume. It is not appropriate to characterize all vermicomposts as that nutrient rich. Like thermophilic composting, the feedstocks and prevention of nutrient loss during vermicomposting determine the final nutrient availability. Vermicompost made from food scraps, coffee grounds and leaf mold has lower nutrient availability compared to dairy manure vermicompost and can be used for transplants at much higher rates, possibly 100% of the medium.

Since 2010 MSU has provided funding for research of on-farm composting and vermicomposting of food scraps at the MSU Student Organic Farm. Our original proposal was to test the use of a hoophouse for developing on-farm vermicompost systems. Four years later, we have learned a great deal about how vermicompost can be produced on farm with lower cost small-scale methods. Worms have survived the winter in composting systems in a high tunnel for all four winters, including the extremely cold season this past winter. We are now beginning to evaluate the vermicompost for transplant production. A key question to address is whether vermicomposts are different from hot composts made with the same feedstocks/ingredients and if so how. The Cornell research project mentioned previously did find a difference.


One alternative to liquid fertilizers during production or prior to setting out is to add a top dressing of mature compost with soluble nutrients to the surface of the trays or flat prior to an irrigation. In some sense this is comparable to making a water extract of the compost (5 to 1 or 10 to 1 dilution) for use as a soluble fertilizer. Top dressing may be suitable for lower numbers of flats (<100). A cup (range 0.5 to 2 cups) of screened compost or vermicompost can be sprinkled uniformly over a flat in about the time it would take to water the flat. One of the keys is have a mature compost or vermicompost with balanced soluble nutrients. That may mean adding minerals during the composting process.

Improving Nutrient Capacity

Perlite and vermiculite are mined minerals that are heated to high temperature (>1000oF) to provide a rapid expansion like popcorn. The lightweight materials help provide structure to root media (perlite) and water- and nutrient-holding capacity (vermiculite).

When considering on-farm alternatives, one possibility is the use of biochar. It is very likely that biochar will provide aeration, structure and water- and nutrient- and biology-holding capacity in lightweight container media. If purchased, the cost of the biochar at the quantities needed is a key factor for consideration; on farm production of biochar is an option as well.

Improving on transplant production is both a short- and long-term investment in the farm. Focus on the basics by developing an action plan, as well as key variables like compost for the transplant media. Both can improve overall farm performance.

John Biernbaum is a Professor of Horticulture at Michigan State University, where he teaches greenhouse management, organic farming principles and practices, organic transplant production, and compost production. See his website for more resources on organic transplant production, crop planning, transplant action plan, transplant fertility management and vermicomposting.

From the November | December Issue

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