The first saguaro fruits of 2018 on a cactus growing only 15 feet from my front door. The brilliant scarlet fruits resemble flowers, and people unfamiliar with saguaros often mistake them for such, but they are fruits that split open when ripe. This is actually a similar strategy as showy flowering is, however, in that the noticeable red fruits are designed to attract the attention of birds, who consume the black seeds laced through the red pulp and fly away to disperse them all over the landscape. This helps to ensure genetic diversity and optimal colonization of new habitats, since birds are among the most mobile of seed dispersing animals.
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The first saguaro fruits of 2018 ripened and split open today in my garden. For some reason, unknown to me, both 2016 and 2017 were really poor years for flowering and fruit set in my domestic saguaro population. This was true for both the cultivated ones in my gardens and the wild ones on the nearby hillsides. I’ve noticed this on-off pattern for the past 19 years that I’ve lived in Arizona, with a heavy blooming and fruiting year being followed by at least one and sometimes two poor years.

One of the ironies of this pattern is that more than once I have noticed that the poor blooming years were after wet winters, and that often dry winters (like 2017-2018 was) can lead to extra flowering, at least locally here at the northern ends of wild saguaro country. I honestly don’t know why this seems to be the case, however, and it also does not seem to be true farther south and closer to the main habitat range of saguaros, where saguaros seem to bloom with at least normal abundance in almost every year, rather than this strange on and off cycling I’ve observed here in the northern Sonoran Desert.

This saguaro is only about 10 feet tall and just reached blooming age a few years ago at about 8 feet tall. It was photographed in late April 2018 and was the first saguaro in my garden to flower, beating the others by about 3 weeks. Some of the later-opening buds did successfully pollinate with others nearby and have set fruits, but since this individual was so premature, the flowers shown here bloomed in isolation, were not fertilized, and dropped off. The fruiting plant that led off this post was much more typical of the majority of saguaros locally, opening its first flowers in the third week of May. With plenty of nearby others to cross-pollinate, fruit set on those was heavy, as shown above.
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It should be noted that there is no evident link between having a dry winter and improved flowering in any other desert plant species I’ve seen. It’s only limited to saguaros, and it makes sense that it would not apply to any other species (succulent or not) and that the good blooming years are after normal to wet winters. One theory for this counterintuitive behavior might be that since saguaros are the largest succulents in the United States, that adult plants have the stored internal water resources to bloom even in the most drought-stricken years, and that they capitalize upon reduced floral competition in these dry seasons by blooming when little else does. When saguaro flowers are among the only sources of nectar and pollen around, my hypothesis is that the overall population benefits from increased attention by the available pollinators, resulting in better fruit set, and later on from more effective seed dispersal as animals eat what is probably the main or only food source in a dry year. In wetter years, when everything else is also in bloom and in fruit, could it be true that saguaros hold off, don’t flower as much, and somehow “know” that competition would be high for pollination and seed dispersal? It’s one possible explanation, although I have no way of testing this.

One other possible explanation I can think of is that since saguaro seeds do not germinate well, or at all, in the cold winter months and germinate almost entirely with warm summer monsoon rains, that there is no immediate benefit to heavy reproduction after a wet winter since it is basically irrelevant to seedling germination and survival, at least for the first year. However science has shown us that generally a drier winter leads to an earlier onset of the summer monsoon season in the desert southwest. The reason for this is because a dry winter means less snowfall in the mountains of the Sierra Nevada, Great Basin Ranges, and Rocky Mountains, all of which are located far north of the Sonoran Desert. Less snow coverage in early and midsummer means that the strong and dry high pressure systems that develop over the Great Basin, California, Colorado Plateau, and Four Corners regions can kick off sooner, because it is these highs to the north of the Sonoran Desert that set up the southerly wind flow patterns that bring abundant tropical moisture out of both the Eastern Pacific and the Gulf of Mexico, leading to the desert monsoon season. When montane snow cover is high after a wet winter, the mountain air is cooler and moister, which delays the onset of the high pressure systems and reduces their strength, so the summer monsoon in the desert is often weaker and later than in dry years. And perhaps the local saguaro population has over eons adapted to this pattern by blooming more in dry years in anticipation of a stronger, wetter monsoon?

Whatever the case, this was a dry winter, and in my area the saguaros are fruiting well in contrast to everything else, and I hope that this might mean a good summer monsoon. It also means that I can finally spend some time harvesting buckets of fruits, the large majority of which will be processed for seeds, which I can sell online. Now that we have a good fruit year I hope to gather several pounds of seed, which can potentially mean 8 to 10 million new seedlings when sown in greenhouses and a couple thousand dollars in income. In a week or two when there are many hundreds of fruits all ripening at once, I’ll spend a couple of days doing gathering them and processing for seeds. (I’ll eat a few too – they are quite tasty!) Stay tuned….