Growing Plumerias In Phoenix Arizona
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Obtusa plumerias will sun burn in the Arizona summer when subjected to full sun, so at the least they should be placed where they will receive afternoon shade. The ideal condition for an obtusa plumeria in Phoenix is filtered sun, such as under a tree with a light canopy. In filtered sun it will get enough sun to bloom but will not be over exposed.
Rubra plumerias are much more heat tolerant than Obtusas. In fact, they can take full Phoenix summer sun. Their leaves tend to burn some during the hottest driest months but no more than plants such as citrus which are typical full sun plants here. The flowers do not take the heat as well as the leaves and for this reason a rubra will be more attractive if it gets afternoon shade. If moving a plumeria from shade to sun be sure to do so gradually. Like all plants, plumerias will burn if suddenly moved from a low light to a high light environment.
Plumerias go dormant when night time temperatures go below 50 degrees. Usually they will shed their leaves when going dormant but sometimes they will just stop growing. Rubras lose their leaves more easily than obtusas do, resulting in rubras being more cold hardy. This is the reason I put my rubras in the ground and my obtusa in a pot. Many references state that Plumerias cannot take temperatures below 40 degrees F. Through experience, I have found this not to be the case. In fact, I have a rubra in my back yard, planted in the ground, that was subjected to temperatures as low as 33 degrees (December 2003) without damage.
Planting in the ground
Dig a hole at least twice the size of the rootball. At a minimum, make the hole 2 feet in diameter and 2 feet deep. Back fill the whole with the same native soil that was removed. It also is a good idea to finish with the hole an inch or two recessed so that a watering basin is formed. After planting, spread a thin layer of compost on top of the soil to help conserve moisture and to supply some nutrients. Do not fertilize the newly planted tree until it has been vigorously growing for a couple of months. Plumerias tend to have a flimsy foundation of roots when they are young, especially if they are grown from a cutting, so it is good to tie them to a strong wooden stake when planting.
Planting in a pot
Plumerias are trees, so they should be planted in the largest pot that can be safely moved around. A light porous soil is best because it will allow water to flow through and out of the base, which helps to reduce the accumulation of salts present in Phoenix water. A stake should be used to prop up the plant until its roots have sufficiently anchored it. This usually takes about a year. Most plumerias are grown from cuttings and have flimsy anchorage until they are well established.
Watering frequency in the ground
Plumerias can be grown on either a citrus watering schedule or a grass watering schedule. However, they are generally more healthy on a citrus schedule so a grass schedule should only be used if there is no other choice. On the grass schedule it is recommended that they not be grown actually in the grass, because being surrounded by thatch will keep them too moist and will most likely result in root rot.
Watering frequency in a pot
Plants in pots always need more watering than those in the ground. In the summer, a plumerias big leaves will facilitate a lot of evaporation so it will need to be watered at least twice a week if not more often. In the winter, a dormant plant should be kept fairly dry. A 100% dormant plant can probably be watered once a month, while a plant that hasn't lost all its leaves but is not really growing can be watered about every two weeks.
Watering method in the ground
Basin or flood irrigation is recommended because it helps keep the salt in our salty water from accumulating around the roots. Furthermore, deep watering will encourage the plant to develop deeper roots, making the plant tougher when the weather gets hot and dry.
Watering method in a pot
If the pot is outside, the plant can just be watered until water starts pouring out the bottom. Obviously in the house this would make a mess, so the plant can be watered until water starts to come through into the saucer. However, if the plant is always kept in the house it is recommended to flush water through the pot every now and then to reduce salt build up.
Fertilizing and Growth Rate
Plumerias grow rapidly and are therefore heavy feeders. During the growing season, a plumeria can be fertilized every one to two months using a high phosphate water soluble fertilizer. They should not be fertilized during the cool time of the year when they are dormant or nearly dormant. I currently use a combination of fish emulsion 0-10-10 and 5-1-1 to fertilize my plumerias.
Plumerias can be pruned to promote a desired shape. However, they tend to branch less vigorously than your average plant, so it is difficult to truly shape them. The good thing about their lack of branching is that it results in thick branches and a fairly open canopy which is part of what makes them look exotic. If one attempts to shape a Plumeria they should keep in mind that branching habits are dependant on the cultivar. For example, a Singapore Obtusa can be more easily trained into a compact form than most Rubras. This makes the Obtusa a better potted plant.
Plumerias are usually propagated by cutting and grafting. The links below lead to very good sources on how to best do this.
Plumerias have no significant bug problems in Arizona. However, they can get black tip rot when emerging from dormancy in the spring. Black tip turns all of the growing tips black and also creates associated pockets of black liquid. This can kill the plant if left to persist for a long time. However, it does result in the plant branching, so if it's quickly cured it can actually have benefits. In Phoenix, putting the plumeria in full sun cleans up black tip in a couple of weeks or less. Full sun might not be an option in the middle of summer (see heat tolerance above). Black tip is a fungus so the sun simply dries it out. In humid climates this technique might not be as effective, so fungicides might be necessary.
Greenhouse white flies can be a problem with plumerias kept indoors. The type of white fly that comes out in swarms in July in Phoenix appears to not bother plumerias at all. I believe this is the citrus white fly. However, the green house variety will multiply like crazy on your plant. The greenhouse variety does not live in AZ but if you're unlucky you'll get it when you mail order a plant from somewhere more tropical, like I did. White flies are resistant to every pesticide known to man and are therefore almost impossible to kill. The solution? Cut off all of your plants leaves, put them in a plastic bag and soak them with pesticide and throw them in the trash. A healthy plumeria will survive this but might decide to go dormant for a while before popping out leaves just to make you worry.
More Photos of Plumerias Growing In the Phoenix Area
Here is an additional page showing Plumerias growing in the lower desert. If you would like to contribute a picture to this page, please feel free to e-mail your digital photo, along with an explanation of where you live, your plumeria variety, and anything else you would like to add. More Plumeria Photos
Links to more plumeria information
The Tucson Gardener