Kratom (Mitragyna speciosa) is a tropical evergreen tree in the Rubiaceae family, native to the humid wetland forests of Southeast Asia including southern Thailand, Malaysia, Indonesia (notably Borneo and Sumatra), and parts of Myanmar. It has also been introduced to other regions such as the Philippines and New Guinea (Takayama, 2004; Eisenman, 2014; Cinosi et al., 2015). The leaves of kratom are rich in bioactive alkaloids and have been used by outdoor laborers in Southeast Asia as a stimulant and mood enhancer, helping them endure long hours of physical labor while under intense climatic conditions (Singh et al., 2019). Beyond its stimulant properties, kratom has also been used to treat various ailments, including pain, diarrhea, hypertension, fever, and wounds, as well as to alleviate opioid withdrawal symptoms (Cinosi et al., 2015; Singh et al., 2017, 2019).

During the last two decades, kratom has gained increasing attention in Western countries. Historically, Southeastern Asians have utilized the analgesic properties of fresh leaves by chewing on or steeping them in hot water to brew tea [Eisenman (2014); Huisman et al., 2023]. Over time, concentrated kratom leaf extracts have been produced as an oral supplement to alleviate pain and sold to countries that do not have kratom naturally (Brown et al., 2017; Sharma et al., 2019; Huisman et al., 2023). The rise in kratom use in the West is largely linked to the ongoing opioid crisis, with many individuals turning to kratom for relief of pain, anxiety, and depression (Garcia-Romeu et al., 2020). Similar to its traditional uses, some Western users also rely on kratom to reduce opioid consumption (Garcia-Romeu et al., 2020). Approximately 10–15 million people in the U.S. are estimated to consume kratom regularly (Henningfield et al., 2022), which requires the importation of nearly 2,000 metric tons each month (Shah et al., 2021). As a result, the U.S. kratom industry generates $1.2 to $5.0 billion in revenue annually (Botanical Education Alliance and American Kratom Association, 2016). However, there is no commercial production of kratom in the U.S., and no cultivation protocol is available for kratom propagation and production.

Propagation is a crucial initial step in the crop production cycle. Due to low seed viability and poor germination rates, kratom is propagated through stem cuttings. The success in cutting propagation is influenced by several factors, including plant genetics (Leakey et al., 1994; Marques et al., 1999), mother stock plant health and age (Tchoundjeu et al., 2002; Bhardwaj and Mishra, 2005; Amri et al., 2010), temperature (Owen and Lopez, 2018), humidity and vapor pressure deficit (Will et al., 2013), light (Craver et al., 2019; Owen and Lopez, 2018), season (Ayoub and Qrunfleh, 2006), cutting positions (Bhardwaj and Mishra, 2005), hormone application (Tchoundjeu et al., 2002; Bhardwaj and Mishra, 2005; Amri et al., 2010), rooting substrate composition (Tchoundjeu et al., 2002), and propagation systems (Tokunaga et al., 2020; Weingarten et al., 2024). To our knowledge, no studies to date have explored the factors influencing kratom’s vegetative propagation.

Rooting hormones and rooting substrates can significantly affect rooting success. Applications of synthetic rooting hormones, such as indole-3-butyric acid (IBA) and naphthalene acetic acid (NAA), to stem cuttings generally accelerate initial root development, improve rooting uniformity, and reduce rooting times by mimicking their natural auxin, indole acetic acid (IAA) (Cerveny and Gibson, 2005; Owen and Lopez, 2018). Thus, IBA and NAA have been used to propagate a wide range of crops, including coleus (Coleus scutellarioides), camellia (Camellia japonica), euonymus (Euonymus kiautschovicus), chrysanthemum (Chrysanthemum × morifolium), pfitzer juniper (Juniperus × pfitzeriana), Manetti rose (Rosa × noisetteana), and apple (Malus domestica) (Blythe et al., 2007). Soilless substrates formulated by optimizing peat, vermiculite, and perlite in different proportions are used for rooting stem cuttings. A higher percentage of peat in the substrate significantly increased root number and the length of the longest root in Ilex ×meserveae (Maynard, 2000) and improved rooting percentage, root length, and root quality score in Lobostemon fruticosus (Swarts et al., 2018). Vermiculite, which offers both good water retention and aeration, has been shown to improve rooting of tropical crops such as spiked pepper (Piper aduncum) (Gomes and Krinski, 2018), oleander (Nerium oleander) (Ochoa et al., 2002), and papaya (Carica papaya) (Kaity et al., 2007). In our preliminary trials, different concentrations of rooting hormones and substrate compositions (combinations of peat, perlite, and vermiculite) were evaluated for rooting kratom cuttings. Results indicated that substrate composition had minimal effect on rooting success and cutting quality. Higher hormone concentrations (e.g., 2,500 mg/L IBA/1,250 mg/L NAA and 7,500 mg/L IBA/3,750 mg/L NAA) provided limited or even negative effects on rooting, suggesting that further investigation into lower hormone concentrations was warranted.

Light plays a vital role in root initiation and subsequent plant growth. Higher photosynthetic daily light integral (DLI), achieved through longer photoperiods or supplemental lighting, can significantly enhance callus formation and rooting quality. Currey et al. (2012) found that an increase of DLI from 1.2 to 12.3 mol·m^-2·d^-1 led to a substantial increase in root dry mass by 156% to 1137% across nine tested species and improved the quality index by 176% to 858%. Similarly, an additional DLI of 3.6 mol·m^-2·d^-1 supplemented by LED lighting significantly enhanced the rooting percentage, root length, root number, and root dry mass of carnation (Dianthus caryophyllus) cuttings in 10 days, and further increased root dry mass 15 days later (Wang et al., 2020). While a DLI of 3–8 mol·m^-²·d^-¹ is generally recommended for callusing and 5–10 mol·m^-²·d^-¹ for root development, these recommendations are primarily based on studies involving floriculture crops (Faust et al., 2016). More recent research suggests that a DLI of 10 to 12 mol·m^-²·d^-¹ is optimal for cutting propagation of culinary herbs (Kohler and Lopez, 2021). While much of the existing research on light requirements during propagation has focused on increasing DLI through supplemental lighting, relatively little attention has been given to the role of photoperiod. Preliminary observations from our team suggest that kratom may be photoperiod sensitive. Therefore, understanding the impact of photoperiod on kratom propagation is essential for developing effective lighting guidelines.

Overhead misting is a widely adopted method in greenhouse propagation of cuttings. This approach often involves intermittent misting on benches to maintain humidity around cuttings. However, excessive misting can cause waterlogging and oxygen deficiency, resulting in poor rooting efficiency. The use of overly cold water for misting can lower soil temperature and slow down rooting. Multiple preliminary trials conducted by our research team using a greenhouse misting method yielded suboptimal results ( Figure 1 ), marked by low rooting success, high variability, and prolonged rooting process (8–10 weeks). These outcomes highlight the need to explore alternative propagation systems for more consistent and efficient propagating kratom. Recently, new techniques, such as aeroponics, have been developed for improving rooting efficiency. Aeroponic technology offers several advantages, including superior aeration in the root zone, enhanced water and nutrient use efficiency, year-round cultivation, and a faster production cycle (Kumari and Kumar, 2019). Mehandru et al. (2014) demonstrated that an aeroponic system without the use of IBA significantly improved the rooting of Leptadenia reticulata. The rooting percentage increased by 38%, the number of roots per cutting by 2.9 times, and the length of roots per cutting by 1.7 times compared to conventional soilless propagation media. Similarly, Weingarten et al. (2024) reported that aeroponic propagation produced significantly better root quality in two Cannabis sativa cultivars compared to foam and rockwool media. Additionally, aeroponic propagation is typically conducted indoors, where environmental conditions are more stable and easily controlled. This indoor setting offers additional benefits, such as reducing crop losses, increasing productivity per area, and accelerating rooting (Gibson et al., 2020). These advantages make aeroponic systems an appealing option for propagation of kratom cuttings.

With the rising interest and demand for kratom, coupled with a lack of foundational knowledge on its propagation, the objectives of this study were to (1) compare the rooting success of an indoor aeroponic system with a greenhouse mist system; (2) examine the effects of different photoperiods on root development; (3) investigate the impact of rooting hormone on propagation of three cultivars in both systems; and (4) assess rooting success and performance among three kratom cultivars.

Propagation of cuttings under a controlled indoor environment holds great potential and offers many benefits for year-round, high-quality transplant production compared to conventional greenhouse mist systems (Gibson et al., 2020). In some woody species, the window for successful rooting is brief, typically occurring from late spring to mid-summer when trees are actively producing new shoots (Cameron et al., 2005). Similarly, in this study, kratom cuttings propagated under a greenhouse mist bench exhibited drastic seasonal variability in rooting success (ranging from 7% to 98%) and inconsistent root growth, sometimes comparable to, but often poorer than, that achieved in indoor aeroponic systems. Under natural conditions, kratom’s active growing period generally spans from April through September, though the use of heat-retentive shade structures can extend this into the winter months. Despite such season-extension techniques, traditional greenhouse mist benches may still fall short in winter due to lower temperatures, reduced humidity, and insufficient photoperiod and DLI. Such factors are particularly limiting for tropical species like kratom. In contrast, indoor aeroponic systems provide a controlled environment that eliminates seasonal fluctuations, consistently delivering high rooting success with better root quality, even for hard-to-root cultivars such as ‘Hawaii’. In this study, root initiation in aeroponic systems occurred reliably between weeks 3 and 5, regardless of cultivar and DLI, with roots fully developed and ready for transplant by week 6 ( Figure 4 ). This approach effectively shortens the typical 8- to 10-week propagation cycle observed in greenhouses, even under optimal seasonal conditions. Collectively, our findings support the use of indoor aeroponic systems as a reliable method for year-round production of high-quality kratom cuttings, particularly for challenging cultivars. Greenhouse mist systems, on the other hand, can serve as a cost-effective alternative for propagation during favorable seasonal windows.

Light substantially affects the rooting success of cuttings (Koski et al., 2024), as root initiation, growth, and development depend on an adequate supply of carbohydrates produced through photosynthesis, of which DLI is a crucial factor. DLI can be increased by either raising the instantaneous light intensity or extending the photoperiod. While most propagation studies have focused on increasing DLI through supplemental lighting (Currey et al., 2012; Lopez and Runkle, 2008) or adjusting the photoperiod of stock plants (Koski et al., 2024; Whalley and Cockshull, 1976), relatively few have investigated how photoperiod alone affects rooting success in stem cuttings. Nanda et al. (1967) reported that a short-day photoperiod is necessary for successful root initiation and development in Bryophyllum tubiflorum stem cuttings. In the present study, a photoperiod of 14 hours resulted in the most favorable rooting outcomes in kratom cuttings. Because all cuttings were rooted in identical aeroponic units under well-controlled indoor conditions, seasonal effects were minimal. As shown in Table 3 , cuttings exposed to the 14-hour photoperiod showed the most total root length, projected and surface area, root volume, and number of tips, forks, and crossings. According to Waisel et al. (2002), root projected area represents the root’s appearance on a two-dimensional plane, while surface area refers to the total external area, including root hairs, folds, and irregularities. Both metrics reflect the root’s potential to absorb water and nutrients, which supports plant growth and longevity. Similarly, Cao et al. (2023) described total root length as an indicator of a root system’s development and elongation capacity, with root tips reflecting the physiological metabolic activity. Root forks indicate the breadth of its distribution, while root crossings, encompassing both central and lateral roots, illustrate the root system’s horizontal and vertical distribution area. These traits collectively highlight the critical role of root architecture in supporting metabolic function and resource acquisition, making them strong predictors of transplant survival and long-term plant performance (Larson et al., 2020). Our findings suggest that a 14-hour photoperiod promotes the highest root system functionality in kratom cuttings, indicating enhanced water and nutrient uptake efficiency, as well as improved post-transplant survival. Interestingly, this photoperiod aligns closely with the natural day length in Southeast Asian [typically ranging from 11 to 13 hours year-round (Sengloung et al., 2009; Rengasamy et al., 2022)], the region where kratom is indigenous (Oliveira Neto and Gonçalves, 2019). These results highlight the value of further research to validate the findings and explore how varying light intensities, under a fixed photoperiod, affect kratom rooting, thereby refining lighting guidelines for propagation protocols.

Significant differences in root initiation and root growth were observed among the three kratom cultivars. ‘MR-Malaysian’ consistently demonstrated the highest rooting success and root growth characteristics when rooted in an indoor aeroponic system. Root initiation for ‘MR-Malaysian’ typically occurred within 3 to 4 weeks, depending on seasonal variations, and full root development was generally achieved by week 6. ‘DR-Bumblebee’ exhibited root morphological characteristics comparable to ‘MR-Malaysian’, but with a slightly lower rooting success rate and fewer root numbers overall. Root initiation in ‘DR-Bumblebee’ typically lagged by about one week compared to ‘MR-Malaysian’. Despite this delay, ‘DR-Bumblebee’ was still able to complete root development and reach transplant readiness within the same 6-week cycle. In contrast, ‘Hawaii’ was the most challenging cultivar to root, with rooting success rates typically below 50%. Although root initiation generally occurred between weeks 4 and 5, which is similar to ‘DR-Bumblebee’, the subsequent development was significantly slower. In most cases, ‘Hawaii’ plants were not ready for transplant by the end of week 6, indicating a need for a more extended rooting period or potentially modified propagation conditions to improve outcomes. A similar trend was observed in the greenhouse mist system, although overall rooting performance was lower compared to the indoor aeroponic system.

Plant hormones, primarily auxin, play a crucial role in the propagation of various propagules (Halliday et al., 2009). Since the 1930s, IBA and NAA have been widely used in the horticulture industry for effective rooting of stem cuttings (Sun et al., 2023). Plant responses, however, vary depending on the concentration and formulation of the hormones (Kroin, 2008; Sun et al., 2023). For quick dips, concentrations of 150–500 mg/L are commonly used for herbaceous plants, while 1,000 mg/L is often applied to softwood cuttings (Kroin, 1992). Soaking treatments typically use lower concentrations, ranging from 20–200 ppm for 24-hour exposures (Eigenraam, 2011; Davies et al., 2018). Given that our indoor aeroponic system continuously exposed the cutting base to hormone solution over six weeks, we opted for a lower concentration based on our preliminary, anecdotal observations that higher concentrations, such as 2,500/1,250 mg/L or 7,000/3,500 mg/L IBA/NAA, did not enhance rooting success in kratom and, in some cases, appeared detrimental. Thus, we used 5 mg/L IBA and 2.5 mg/L NAA in this study, which slightly improved kratom rooting percentage and root quality, particularly in aeroponic systems, compared to water control. Although most improvements were not statistically significant, the hormone treatment did significantly increase final root number in the aeroponic system across all three cultivars. This may suggest that the endogenous auxin produced by young kratom shoots and transported to the base of the cuttings is likely sufficient to initiate adventitious root elongation and lateral root emergence. However, exogenous auxin applications appear to support further development. Notably, hormone treatment helped reduce the disparity in rooting performance between easy- and hard-to-root cultivars. For example, in aeroponic systems, the application of rooting hormones reduced the differences between ‘Hawaii’ and the other two cultivars in final root number and root dry mass from 144-169% and 113-123% to 42-78% and 75-82%. This suggests the potential for using rooting hormones to enhance propagation outcomes in challenging genotypes. Further research using a broader range of hormone concentrations is warranted to explore their benefits fully.

Aeroponic propagation offers advantages in reducing the risk of soil-borne diseases. However, it may spread diseases if the solution or propagules carry over pathogens. In this study, Fusarium was observed on several kratom cuttings in the indoor aeroponic system. Early symptoms included dark brown necrosis at the cutting tips, often accompanied by a white to translucent gelatinous substance. By Week 4, the percentage of cuttings discarded due to severe Fusarium infection was 11% for ‘MR-Malaysian’, 5% for ‘DR-Bumblebee’, and 28% for ‘Hawaii’. Nonetheless, the cultivars still achieved relatively high rooting success rates: 71–75% for ‘MR-Malaysian’, 57–60% for ‘DR-Bumblebee’, and 38–41% for ‘Hawaii’, suggesting that Fusarium infection did not universally prevent root development. However, the lower rooting success observed in ‘Hawaii’ may still be partially attributed to Fusarium infection. Interestingly, under identical propagation conditions and sanitation protocols (outlined in the Methods section), ‘MR-Malaysian’ appeared to be the least susceptible to Fusarium, while ‘DR-Bumblebee’ and ‘Hawaii’ showed greater vulnerability, possibly due to differences in genetic resistance or tissue sensitivity. The infection likely originated from contaminated cuttings, either due to latent infections in stock plants or contamination during handling. This highlights the need for stricter sanitation protocols, particularly in systems prone to pathogen spread, such as aeroponics. In addition to standard sterilization, enhanced measures, such as stock plant disinfection, cutting surface treatments, and targeted fungicide applications, may be crucial in preventing the spread of Fusarium and other potential pathogens, thereby ensuring successful propagation.

To the best of our knowledge, this is the first study to examine the combined effects of multiple factors on kratom cutting propagation across two different cultivation systems. The indoor aeroponic system consistently yielded higher rooting percentages and enhanced root growth throughout the year, whereas the greenhouse mist system demonstrated inconsistent rooting success and variable root growth. A 14-hour photoperiod produced the most favorable rooting performance in kratom cuttings. Among the three kratom cultivars tested, ‘MR-Malaysian’ consistently outperformed the others, showing a high rooting success rate, desirable root morphology, and a relatively short production cycle. ‘DR-Bumblebee’ ranked second in performance, while ‘Hawaii’ was the most challenging cultivar to propagate, with the lowest rooting success rate and the longest production time. The aeroponic system, however, may be susceptible to disease spread if proper sanitation is not maintained. Nevertheless, this study highlights the importance of photoperiod, propagation systems, and cultivar selection in the successful propagation of kratom cuttings. Further research is needed to optimize each of these factors for further improving the efficiency of propagating this valuable medicinal plant.