The learning of plants has garnered considerable attention in recent years, but students often lack the motivation to learn about the process of plant growth. Also, students are not able to apply what they have learned in class in the form of observation, since plant growth takes a long time. In this study, we use augmented reality (AR) technology to develop the ARFlora system, which can assist students in observing the changes in plant growth while in the classroom. More specifically, students are able to use AR markers to manipulate various virtual objects (e.g. sunlight) and observe the changes they have on plant growth. Meanwhile, a quasi-experimental evaluation is in place to substantiate the effectiveness of ARFlora in the learning of plants and to compare it with digital video learning. In the quasi-experimental design, 55 elementary-school students participated in the study. The participants are divided into two groups, an "experimental group" and a "control group." The experimental group was taught using the ARFlora system, while the control group was taught by employing the digital video. Results show that (1) ARFlora and digital video have the same effectiveness on student's learning outcomes; (2) ARFlora is more effective in helping students retain learned knowledge; and (3) ARFlora is comparatively more useful in motivating students to learn about plants.