Background: There is often a period of uncertainty between the initial studies of a phenomenon and the publication of a comprehensive meta-analysis. During this time, yes-or-no decisions are made about the effectiveness of interventions based on individual studies and their statistical significance. In living systematic reviews, studies are compiled and added to the analyses as they emerge. An updatable website can be employed for researchers to view the most up-to-date effect size for a phenomenon based on all available studies, and to which researchers can add effect sizes from their own studies. Figures on the website include findings from conventional null-hypothesis significance testing and updating meta-analyses. In this paper, we describe the benefits of updating meta-analyses when studying the effects of nature-based wellbeing interventions on positive and negative affect. Research Questions: We report findings from updating meta-analyses from available studies that have examined the effects of nature-based wellbeing interventions. We also describe how different methods for analyzing the data can produce different conclusions, with a particular focus on the differing findings from significance testing and meta-analyses. Sample characteristics: Our sample consisted of 11 studies of nature-based wellbeing interventions that used a randomized-controlled design, included a control group, and measured positive and negative affect. Design: Findings are reported from updating meta-analyses and null-hypothesis significance testing. Results: For positive affect, all methods demonstrated a positive effect of nature-based wellbeing interventions. For negative affect, conventional methods were inconclusive, whereas the updating meta-analysis revealed a small but non-zero negative effect size. Scientific contribution: The availability of findings from updating meta-analyses in a website format promises to be a useful tool for positive psychology researchers. It can reduce confusion and direct research efforts. Researchers need not spend time tracking down previous studies; effective interventions can be recognized as such earlier on in a study sequence.