Biochar has been heralded for improving soil quality, sequestering C, and converting organic residues into value‐added amendments. Biochar research in agricultural settings has been primarily conducted on acidic soils, with few studies evaluating biochar effects on alkaline soils. Given the rise of small‐scale, sustainable farmers experimenting with biochar in South Florida's alkaline, carbonaceous soil, this study sought to assess biochar use in South Florida using an invasive plant species as a feedstock. Melaleuca quinquenervia (Cav.) S.T. Blake biomass was converted into biochar to measure how application at two rates, 2 and 5% (w/w), affects plant growth, soil macro‐ and micronutrients, and microbial gas flux (CO2) in a potted greenhouse experiment using Phaseolus vulgaris L. Plant growth was inhibited with biochar addition at the 2 and 5% rates. Dry shoot, pod weight, and pod length decreased significantly between treatments (P < 0.001). Significant reductions in plant‐available P, Ca, Mg, Cu, and Zn were observed in the 5% biochar soil postharvest (P < 0.05). Compared with the control, addition of biochar at 2 and 5% rates significantly reduced CO2 flux during the growing season, but not at harvest (P < 0.01). Our results indicate that those considering biochar application in South Florida's alkaline soil should be cautious in selecting feedstock and temperature for biochar production. Biochar can be produced at lower temperatures to decrease pH, but the concomitant increase in volatile matter (VM) is of concern. Although CO2 flux may have decreased, the deleterious impacts of M. quinquenervia biochar (pH = 8.12, VM = 26.5%) on P. vulgaris production should not be dismissed. Core Ideas South Florida invasive Melaleuca quinquenervia was used to make biochar. Increasing rates of M. quinquenervia biochar reduced bean growth in calcareous soil. A 5% (w/w) rate of M. quinquenervia biochar reduced available nutrients in soil. Melaleuca quinquenervia biochar addition reduced soil respiration compared with the control.

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In recent years, there has been a greater demand for growing substrates for ornamental plants. However, as cost rises and quantities of these materials become more limited, alternative forms of growing media are now being sought. A study was conducted to test the efficacy of using insect rearing waste as an alternative growing media for plants. Common sunflower (Helianthus annuus L.) and Mexican sunflower (Tithonia rotundifolia (Mill) S.F. Blake) were grown in different ratios of insect colony waste compost (ICW) combined with cardboard (Cb) (ICW+Cb) and nursery mix (NM) mixtures. The purpose of this experiment was to determine whether insect colony waste (ICW) from fruit fly rearing would sustain plant growth. Selective characteristics of the potting substrates revealed that the ratio of 100:0 ICW+Cb:NM had a 7.6 pH, 0.86 dS m -1 EC (salinity), 0.46 g cm -3 bulk density, and 50.1 percent water holding capacity at saturation. For common sunflower, there was a significant difference between the 100:0 and 0:100 ICW+Cb:NM blends for plant height, with the 100:0 ICW+Cb:NM mixture having the greatest height. For the Mexican sunflower, the 100:0 ICW+Cb:NM produced significantly more leaves and had a greater stem diameter than some of the other mixtures of potting substrate. There was no indication that the insect colony waste combined with cardboard (ICW+Cb) would inhibit plant growth. ICW+Cb have the potential to be used as an alternative substrate for growing plants.