Gardenias and Other Acid-Loving Plants in the Low Desert Garden

Some plants are well adapted to the unique and harsh conditions of the Sonoran desert. The saguaro cactus is so comfortable here that it grows almost nowhere else in the world. Though many plants are able to adapt to the Phoenix area, other plants brought in from different climates might not be able to hack it here. 

Unfortunately the gardenia is one of those plants. Gardenias are beloved for their fragrant flowers and dark green foliage but in the low desert they require extra care to keep them healthy. The high pH of our soil is specifically what makes our metro area gardenias look awful and fail before their time. 

Gardenias need acidic soil, and our soil is so basic that it causes nutrient lockout in these plants. They will struggle to grow normally. Chlorosis appears, turning the gardenia a sickly light green color. And the edges of the leaves may crisp and turn brown. Plants may live for several years but they will be constantly stressed and in danger of sudden failure. The gardenia will bloom rarely if at all.  

I haven’t seen any alkaline-resistant cultivars of the gardenia, so the way to fix this problem is to make the soil less alkaline. This is mostly accomplished with humic acid and organic matter.

Gardenias planted directly in the ground should always be top dressed with organic material like fallen leaves or composted mulch to continuously acidify the soil around the roots of the gardenia. Refresh the organic material once or twice a year at least. If you have a patio that collects a lot of fallen leaves, those leaves are excellent mulch for many plants. 

For existing plants in the landscape, use sulfur to rescue a plant suffering from the alkaline soil. Sulfur usually comes as a powder or granule that is applied around the plant’s base and watered in. Sulfur works to lower the soil pH for a while, and needs to be reapplied as symptoms appear. (I haven’t tried vinegar or “pH down” products yet but please let me know if anyone has tried acidifying the water to help a gardenia!)

It’s easier to plant gardenias in pots in the valley. Potting soil will always be more acidic than our desert soil. Potting soil contains mostly organic material like compost, forest products, and coco fiber (I don’t recommend peat based potting soil in the desert because it dries out and becomes unusable during the summer – besides the fact that peat moss mining is highly unsustainable). Gardenias thrive in rich soil. Add an layer of organic mulch when planting and refresh the mulch at least once a year to keep the soil healthy and to replenish the nutrients being used over time. Pots with gardenias do best in light shade outside with protection from the afternoon sun. If growing indoors, consider using an LED grow light if morning sun isn’t available.

Every plant has a different acceptable range of pH. Many plants from other parts of the world have some tolerance for alkaline soil which is why we get to enjoy hibiscus and potato vine and vinca and canna lily in the valley. Gardenia is one of those rare plants that can survive the heat but can’t handle the soil in Phoenix. For all the plants that prefer acidic soil we can try to increase the level of organic material and humic acid in the soil to create a better root environment.

Planting season in the low desert starts in October and goes through April. I’m available in the east valley for landscape consultations, garden design, installation, and seasonal tune-ups. Send a message on my contact form if you’re interested in scheduling a consult, or subscribe here to receive more posts specific to desert gardening. I’m a certified plant nursery profession in the state of Arizona and a Smartscape certified landscaper in Maricopa County.