Container potting soil might not be your most expensive
input, but according to national industry statistics, if you produce ornamental
plants in containers, it is probably the second biggest expense after
labor. What if you could save 13% to 25% on potting media costs for each container produced? What if you could save irrigation and
fertilizer as well, with a simple change? Those are some of the results
that we found with a simple addition of an input and changing the container
media.
Over the last few years, we have been working on adding
horticultural-grade compost to regular container media to "stretch"
the mix and reduce peat usage. We have used combinations of potting media that
we blended, composed of compost and pine bark as well as replaced potting media
with percentages of compost and compared it to the growth of the normal
container media mix for Central Florida. In both cases, compost matched up.
When we blended a mix of 70:30 and 60:40 pine
bark:compost and compared it to the standard grower mix (¾” composted pine bark (50%), Florida
peat (40%), and hardwood (10%), and grew crapemyrtles, we found that the one
gallons all grew the same; no statistical differences in height and width (Fig 1).
We then stepped
up those one-gallon container plants and replanted them into three-gallon
containers and continued to grow them in the same soils as they started. When those plants were ready to harvest,
height and width were measured, there were no differences in height, but
compost soils were slightly wider than the standard with 30% compost being the
widest plants.
In our
demonstrations of replacing a portion of potting soil with 20% or 40% compost
we found similar results with ixora, crapemyrtles, New Guinea impatiens, and a
variety of vinca (another variety did worse than control). All plants grew similarly. Amazingly, when compost was substituted, plants
needed 20-25% less water and 61% less fertilizer. The media costs were reduced
by about 25% or about $0.23 per #3 container. The key takeaway was that
irrigation had to adjust lower to accommodate a more water holding media.
The utilization
of compost is a great way to reduce production costs; irrigation run times and
increase economic and natural resource sustainability. Growers will need to trial varieties and change
how they water to gain savings. Some
plants may not do well in compost. Also,
growers will need to use high-grade, mature compost from a reputable source (ours was donated by Veransa, Seffner) to
avoid pH or nutrient concerns. It also
seems that 20-30% compost is a safe proportion to use, but again testing for
your plants and nursery will influence that amount.
For full
information on this topic the article will appear soon in the proceedings of the
Florida State Horticultural Society.
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