Weird wet weather has Joshua trees flowering early — or late? Help the Yoder Lab map this “bonus bloom” to understand why

Joshua trees are ending 2025 by throwing us a curveball — they’re flowering! Many contributors to iNaturalist have recorded observations of the trees flowering in the last month or so. The normal flowering season for Joshua trees starts in late February into April. So these flowers are either very late for 2025, or quite early for 2026. What’s going on? Read on for a possible explanation — and to learn how you can help us study this “bonus bloom.”

The reason for the anomalous flowering is probably that it’s been an unusual year for weather, with some big early-winter rain events — Lancaster, California recorded two and a half inches more rain than normal for the season so far. Thanks in part to the Yoder Lab’s research, we know Joshua tree flowering is more likely in wet years, and 2025 is not the first time a weird off-season bloom has been recorded. A similar late fall bloom occurred in and around Joshua Tree National Park in autumn 2018 into winter 2019. An analysis by a team at the Florida Museum of Natural History concluded that the 2018 bonus bloom was stimulated by a cool year with unusual rainfall events late in the year, much like 2025.

So the flowers you see right now are Joshua trees’ natural response to weird conditions. Our prior study of the trees’ flowering concluded that global climate change has likely slightly increased the frequency of Joshua trees’ flowering — because the trees are more likely to flower when a wet year follows a dry year, and climate change is driving bigger year-to-year variation in rainfall. Out-of-season rainfall is another possible consequence of the larger change in climate. This might not be good for Joshua trees — which face plenty of other pressures from climate change, development, and wildfires — even if it means they flower more often. For instance, if weird weather makes Joshua trees flower, but it doesn’t also cue specialized yucca moths to come pollinate those flowers, the flowers will be wasted.

We’re still collecting data to better understand what impact this could have, though. That’s where we need your help! Observations contributed to iNaturalist have been critical for our understanding of Joshua tree flowering activity. If you live in the Mojave Desert, or you’ll be visiting soon, you can contribute to the Yoder Lab’s iNaturalist project on Joshua trees and the yucca moths that pollinate them to help us understand what’s going on with Joshua trees right now, and what it means for their future.

There are three main steps to pitching in on this project, and a fourth to take your contribution to the next level:

1. Download iNaturalist

The iNaturalist app is available for both iPhone and Android, and you can even share observations (with dates and location information added) directly from inaturalist.org. Go there to set up a profile and install the app.

2. Join our project

When you’re set up on iNaturalist, navigate to the project page for our study of Joshua trees and their pollinators, and click “join”. This helps us organize records for research. Joining the project will let you send us your observations directly, and give you the option to get updates about our research, and how to help improve the data we get from iNaturalist.

3. Observe some Joshua trees!

Next, go make some records of Joshua trees using the app. This might be right in your backyard or neighborhood, if you live in the Mojave Desert, or maybe on a winter break trip to Death Valley National Park or Las Vegas. We especially need records in the northwestern Mojave, between Lancaster and Lone Pine, California; in Nevada; and in western Arizona. If you see a Joshua tree with flowers or fruits, take a photo with a clear view of the flowers or fruit, then upload it to the app. When you do, you can use options in the app to mark that you see flowers or fruit, and to contribute it directly to our Joshua Trees and Yucca Moths project.

You can also upload photos of trees with no flowers or fruit — they are still really cool looking, and we can use that data, too!

4. If you can, come back later to see if those flowers turned into fruit

If you live close to the place where you make your observations, you can come back a few weeks after seeing flowers to find out whether they’ve become fruit. If they have, yucca moths have been at work! You can take a second round of observations at the same locations as your earlier ones, this time with photos of the fruit, and upload them to iNaturalist again. It’s not just allowed, but encouraged to provide multiple records in the same location, even of the same tree. That will let us track the whole process of flowering and fruiting.

With all these observations, we can continue our work training machine-learning models to predict what weather and climate factors are causing the trees to flower, and what factors cue the moths to know when to emerge and find flowers. Pryce Millikin, the Yoder Lab grad student who led this work, has now graduated, and new arrival Kirsten Zornado has spent her first semester in the lab getting ready to build on Pryce’s work — contributions to the iNaturalist project will provide critical data for her thesis research.

Thanks in advance for your help, and we’ll hope to see you in the iNaturalist app.