Is Epsom Salt The Key To Getting Mandevilla Plants To Bloom? Here's What We Know

Mandevilla plants (Mandevilla spp.) are tropical plants popular for their fragrant flowers ranging in color from pink and red to white or yellow and that primarily bloom in the summer. So, if you have planted them in containers, on trellises, or directly into the ground, it can be frustrating if you do not see their prized blooms. You may have heard of alternative ways gardeners have tried to successfully grow mandevillas and encourage their plants to bloom. One such strategy includes the use of Epsom salt. Although, in theory, Epsom salt could help add magnesium to soil, this is not usually necessary and may do more harm to your plants than good. 

Epsom salt contains magnesium sulfate, a critical ingredient for aiding seed germination and plant photosynthesis. Anecdotally, some gardeners have also reported success with helping their plants flower after adding this ingredient to the soil. Some experts contend this method is also most helpful before you plant seeds or transfer young plants into the ground. On the flip side, other experts believe Epsom salt won't help plants produce flowers at all and that adding magnesium sulfate could decrease calcium intake and destroy your plants. To err on the side of caution, it may be best to determine what else might be ailing your mandevilla plants and perhaps test the soil to see whether they are truly deficient in magnesium before you reach for a bag of Epsom salts to use in your garden.

Unless the ground in your area is naturally sandy, such as in Florida, you may not need to add magnesium to the soil in your garden. If you suspect a nutritional deficiency might be plaguing your mandevilla plants, though, the only way to know for certain is to test the health of your soil. You can DIY with something similar to the MySoil Soil Test Kit – a convenient, cost-effective testing option. As well, plant food that contains magnesium could possibly help. On the other hand, if you choose to try the Epsom salt technique, make sure you dilute it by mixing 1 tablespoon of Epsom salt per 1 gallon of water before applying. Just know that this remedy won't address other possible causes of lack of flowering outside of magnesium deficiency. 

It's also important to know the other factors that might prevent mandevilla plants from blooming. First, keep in mind that these are tropical plants and thus prefer warmer temperatures. If nighttime temperatures are below 60 degrees Fahrenheit, chances are these plants may not flower. Mandevilla plants also prefer partial shade, well-draining soil, and regular pruning sessions. To encourage flower development and bushier plants, pinch up to half an inch from the ends of their stems. Also, be sure to prune old and overgrown stems before springtime to encourage new bloom development later in the season.