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Can sugarcane waste replace some of the peat in potting mix?
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Sugarcane bagasse, the fibre left over after sugar is extracted from the cane, could stand in for part of the peat in a potting mix. In a US greenhouse trial, petunias grown in peat mixes with 15% or 30% milled bagasse grew well, and with less phosphorus fertiliser they flowered more than plants in the standard peat mix.
Peat has long been the backbone of soilless growing media, but rising costs, supply worries and the environmental cost of draining peatlands have growers looking for substitutes. A team from the University of Florida and the LSU AgCenter tested whether aged, hammermilled sugarcane bagasse could replace some of the peat in a standard mix, and whether it could also cut the phosphorus fertiliser petunias need (Vilchez et al., 2026).
What this means for your grow
In this trial, petunias grew well in a peat and perlite mix amended with up to 30% (by volume) aged, milled sugarcane bagasse, and the bagasse added phosphorus of its own. Every mix produced marketable plants, though the coarser 6 mm bagasse at 30% gave lower shoot dry weight than the other bagasse mixes. It was one crop, grown for 66 days, with bagasse that had been aged for 12 months before use, so it is a promising lead rather than a recipe.
What did the team do?
Fresh bagasse from a Louisiana sugar cooperative was left to age for 12 months in a sack in an open-air barn, then run through a hammermill with either a 4 mm or a 6 mm screen. The control mix was sphagnum peat with 15% perlite by volume (peatlite). The team then amended it with bagasse at 15% or 30% by volume, giving five mixes in all, each limed to bring the pH to between 5 and 6.
Petunia ‘E3 Easy Wave Coral’ plugs went into 15.24 cm (6 inch) pots of each mix in a plastic-covered greenhouse, on drip irrigation. Half the plants got a standard fertiliser with phosphorus at 100 mg per litre, and half a reduced one at 30 mg per litre, a 70% cut. The team measured the mixes’ air space, water-holding capacity and particle sizes, then followed plant growth, flowering, leaf greenness, pH and EC every two weeks, before harvesting the plants 66 days after planting.
What did they find?
- The mixes behaved much like the standard mix. Adding bagasse made only small changes to the mix’s physical properties. Container capacity and total porosity were similar to the control. Only the coarser 6 mm bagasse at 30% made the mix significantly denser.
- Plants grew bigger with bagasse. Plants in every bagasse mix outgrew the control plants, at both fertiliser rates.
- More flowers when phosphorus was low. With the reduced phosphorus feed, all bagasse mixes had more flowers than the control by the end of the trial. With the standard feed, flower numbers did not differ significantly.
- The bagasse supplied phosphorus. At the end of the trial, mixes containing bagasse held more phosphorus than the control, and the 30% mixes held the most.
- One mix gave lighter shoots. The 6 mm bagasse at 30% gave lower shoot dry weight than the other bagasse mixes, but root dry mass was similar across all treatments.
- A nitrogen trade-off. Leaves from the control plants had the highest nitrogen. The authors think microbes breaking down the bagasse tied up some nitrogen.
- Little settling. The mixes shrank by less than 1 cm over the trial.
What could it mean?
The authors conclude that hammermilled bagasse can partially replace peat in soilless substrates and support petunia growth, and that it may help reduce peat use and phosphorus fertiliser, particularly where bagasse is locally available. They add that the bagasse they used had been aged for a year, and that more work is needed on how stabilising, processing and ageing change its performance. They also suggest that, because peat is expensive, bagasse could be a filler that helps reduce production costs. For home growers it is a lead to watch rather than a proven swap.
What were the limitations?
- The bagasse was aged for 12 months before use, and the authors say further research is needed to develop practices for stabilising it and to learn how processing and ageing affect its performance.
- The study was not a long-term investigation, so overall breakdown of the bagasse by microbes could not be evaluated.
Trial details
- Who and where: University of Florida (Department of Horticultural Sciences; Department of Soil, Water, and Ecosystem Sciences, UF/IFAS), Gainesville, and Louisiana State University AgCenter, USA. Plants grown on benches in a plastic-covered greenhouse.
- When: bagasse sourced in November 2023 and aged 12 months; plugs transplanted on 21 February 2025; plants harvested 66 days after planting.
- Crop: Petunia × hybrida ‘E3 Easy Wave Coral’, from 3 cm plugs, one per pot.
- Substrate: control of sphagnum peat with 15% perlite by volume; four bagasse mixes with sugarcane bagasse milled through a 4 mm or 6 mm screen and added at 15% or 30% by volume. All limed with 5.33 kg/m³ of pulverised dolomitic limestone to a pH of 5 to 6.
- Containers and watering: 15.24 cm (6 inch) pots; drip stakes delivering 2.3 L/h. From 49 days after planting, about 1000 mL per pot three times a week.
- Nutrition: 200 mL of fertiliser solution per pot once a week from 7 days after planting. Standard rate: 2.22 g triple super phosphate (0-45-0), 3.33 g muriate of potash (0-0-60) and 9.52 g ammonium sulfate (21-0-0), giving phosphorus at 100 mg·L−1. Low rate: triple super phosphate cut to 0.67 g, giving phosphorus at 30 mg·L−1.
- Root zone: substrate pH 5.7 to 7.2 (standard phosphorus) and 5.7 to 7.3 (low phosphorus); EC 0.28 to 0.71 mS·cm−1 and 0.26 to 0.70 mS·cm−1, measured every other week by pour-through.
- Design: completely randomised design; five substrates × two phosphorus rates, 10 treatments, seven replicates each (70 pots). Growth index, flower count and SPAD chlorophyll readings every 14 days on five replicates. ANOVA with Tukey’s test at α = 0.05, in JMP Pro Student Edition 18.
- Results: container capacity, air space at 30% bagasse and total porosity (P = 0.5865) similar to the control; more flowers in all bagasse mixes than the control at the low phosphorus rate (P < 0.0001); higher end-of-trial substrate phosphorus with bagasse; lower shoot dry weight with 6 mm bagasse at 30%; similar root dry mass; highest leaf nitrogen in the control; substrate shrinkage under 1 cm.
- Funding: in part by the US Department of Agriculture National Institute of Food and Agriculture Specialty Crops Research Initiative project Beyond Peat: Substrate Security for a Changing Climate (2024-51181-43290) and the Floriculture & Nursery Research Initiative project Revolution in the Pot (58-5082-3-024 AI).
- Publication: HortScience 61(11): 2561-2567, published online 28 October 2026, https://doi.org/10.21273/HORTSCI19686-26. Licence: CC BY-NC 4.0.
- Not reported in the paper: the greenhouse’s location, temperature, humidity, light and CO2, and conflicts of interest.
Links
- The study: Hammermilled Sugarcane Bagasse Fibers Can Be Used to Reduce Peat and Phosphorus Applications in Petunia Production
- The institution: Horticultural Sciences Department, UF/IFAS, University of Florida
References
- Vilchez, M., Fields, J. S., Abdi, D., Hayes, M. P., & Wilkie, A. C. (2026). Hammermilled sugarcane bagasse fibers can be used to reduce peat and phosphorus applications in petunia production. HortScience, 61(11), 2561-2567. https://doi.org/10.21273/HORTSCI19686-26