Mandevilla is loved all over the world because it blooms throughout the year except for winter.
Trust me, from spring to fall, they bloom every single day. And that is the reason why growers start worrying when they notice Mandevilla is not blooming.
Recently I have been facing the same problem & thereby I dug deep into it & left no stone unturned.
So, If you are wondering why Mandevilla stops blooming, let me explain-
Briefly, Mandevilla quits blooming when they face trouble with daylight, temperature, fertilization, watering, pot size & repotting.
This article covers detailed explanations of these issues with possible solutions.
So, check it out.
Mandevilla/Rocktrumpet Blooming Period
Before starting to look for genuine reasons, you must know when mandevilla blooms & when they don’t.
Mandevilla blooming season starts from late spring to autumn, and they stay dormant during the winter & stop blooming.
During winter, Mandevilla stops growing, blooming, or even sometimes drops older leaves to survive adverse environmental effects.
So, entering the dormancy is the very own physiological process of Mandevilla to conserve energy for surviving the winter season.
Why is the Mandevilla Not Blooming?
1. Light Duration
You may have heard the scientific term “Photoperiodism”, which means light duration. And to amplify its importance, Light duration tops among the factors that can inhibit blooming. Let’s know why-
Mandevilla is a long day-length lover as they need more than 12 hours of daylight for perfect blooming. You might be wondering how day length affects flowering?
Well, day-length or the duration of light triggers a hormone that stimulates Mandevilla blooming.
Thereby, if Mandevilla doesn’t get sunlight for the required duration, it won’t bloom.
Additionally, light intensity also has a serious effect on flowering. A shady place provides less amount of light than a sunny place.
So, in such a situation, how can we push them to bloom?
You know, some things you don’t push, you accept. Day length is a natural phenomenon and meant to be left as it is.
But you might want to be careful about light intensity.
You know, Mandevilla needs 6-8 hours of direct sunlight regularly. But amid scorching sun, Mandevilla wouldn’t mind an afternoon shade. So, keep providing what it needs.
2. Unsuitable Temperature
Internal physiological processes are tough to see. But trust me, the temperature has a direct effect on flowering or bud initiation. Let’s see how it works-
Blooming failure could result from either the lack of flowering promoter or the extreme concentration of a flowering inhibitor. And sometimes both can be responsible too.
Now the question is, how is temperature related to these hormones?
Temperature controls the production rate of promoters and inhibitors of blooming.
So, what is the safer zone here?
Well, Mandevilla came up with elegant blooming while night temperature stays between 60 to 65 °F and day temperature stays above 70 °F.
Furthermore, the unsuitable temperature can increase or decrease the movement of plant food internally & affect blooming.
As it is an environmental factor, you don’t have much to do. But to save your Mandevilla from cold nights, an artificial lighting system could be handy.
Want to know a thumb rule?
Try growing a native variety to avoid such adverse situations.
3. Incorrect Fertilization
During my entire research, the problem I have found the most is -“My Mandevilla is growing but not blooming.” So I kept digging into it & the finding –
Fertilization is a bit tricky when it is a question of blooming. Your Mandevilla not only needs proper fertilizer but also needs them at the right time. So one by one-
As Mandevilla is a flowering plant, the best fertilizer for Mandevilla carries a high phosphorus percentage along with a fitting nitrogen & potassium ratio.
You might be wondering why Mandevilla needs a higher amount of phosphorus. Let me explain-
Mandevilla needs a lot of energy to bloom & that is when phosphorus plays its role. How?
Phosphorus is involved in the internal energy transfer of plants & thus, it stimulates bud development & blooming.
Although, according to nutrient availability in your soil, a balanced fertilizer can also be sufficient for Mandevilla blooms.
When to fertilize Mandevilla?
The right time to fertilize Mandevilla is the growing season & that is- spring and summer.
As they need more food during the growing season, it is necessary to fertilize your Mandevillas every 14 days in spring and summer.
The solution is simple- fulfill its needs in the right amount & at the right time. But keep the following facts in your mind too-
Stop fertilizing Mandevillas in fall and winter. They stay dormant that time.
For potted Mandevilla vines, water-soluble fertilizer (Our Pick: Miracle-Gro Water Soluble Bloom Booster Flower Food) is the best & for grounded vines, use slow-release granular fertilizers (Our pick: Dr. Earth Flower Girl Fertilizer)
Here is a tip- If you don’t want to spend much time fertilizing, use spike fertilizer (Our Pick: Jobe’s Hanging Baskets and Potted Plants Fertilizer Spikes) & relax.
Using too much nitrogen-based fertilizer results in vigorous growth of Mandevilla but eventually reduces the blooming rate. So be careful of that.
Finally yet importantly, for bountiful blooming, get a bloom booster for Mandevilla.
4. Imbalanced Watering
What do you do after fertilizing your Mandevilla? Yes, water it thoroughly. Because water helps the plant to nutrient uptake. But overwatering also can do harm to your plant. Let’s know how improper watering affects your plant.
Every plant absorbs nutrients in a water-soluble form. So, if you don’t water thoroughly, your Mandevilla may face nutrient deficiency.
However, the core issue is, both over & underwatering may force your Mandevilla to stop flowering. How?
Well, during the underwater condition, your Mandevilla loses more water than the supply.
On the other hand, overwatering replaces soil oxygen & troubles your Mandevilla in breathing.
In both cases, the Mandevilla plant falls under stress & tries hard to survive rather than growing & blooming.
Mandevilla requires persistently moist soil during its growing period. As Mandevilla flowers all summer, it may require water three times per week. And almost the same goes for spring & fall too.
Be careful for potted vines as they dry out more often, so keep checking moisture regularly with a moisture meter (Our pick: Atree Soil Soil Tester Kits with Moisture, Light, and PH Test for Garden).
And finally, remember to reduce watering to once every week during winter as Mandevilla enters dormancy.
5. Pot size
If you are growing the vine in a pot, then keep your eyes peeled here-
“Does pot size matter?”- a widely asked question & answer is, yes, it does.
One thing to remember is that your Mandevilla needs pots of the exact size, neither bigger nor smaller. Why?
A larger pot ensures more space for roots to spread. And in that case, Mandevilla puts all its energy into producing roots rather than good flower production.
On the other hand, smaller pots cause pot-bound roots & Mandevilla fall into stress due to high root mass. And the result is-
Mandevilla begins to expose symptoms like stunted growth, poor quality flowers or lack of blooming, frequent wilting & so on.
To make your Mandevilla bloom, start with a 12- to 14 inches flower pot. For existing plants, don’t forget to repot every year with one size larger pot. Our pick-HBServices USA 12″ Self-Watering+ Self-Aerating Round Planter
6. Transplant Shock
It is a common sight of Mandevilla after repotting. Transplant shock occurs naturally & can last for some days.
So I hope you are not still wondering why your Mandevilla is not blooming after repotting or a transplant. Let’s know in detail-
Newly repotted or transplanted Mandevilla faces several stresses like poorly established roots, environmental changes, etc. Why?
It is because plants have to adapt to the new environment after transplanting & it takes time.
So, if you are getting no blooms after repotting, consider it is because of the shock.
The best time to repot Mandevilla is early spring because it is when the growing period starts.
But, if your plant is already in shock, try gradual hardening by gradually exposing it to direct sun. And also take proper care with proper watering.
Additionally, you can use Epsom salt in your Mandevilla for new growth as blooming occurs in new branches.
Last but not the least, try not to damage the root during repotting & ensure enough drainage holes in the pot.
Flowering plants like Mandevilla are grown for their luxurious blooms. Therefore gardeners go crazy when the plants quit blooming.
As you have gone through this article, now you know all the possible reasons that can be responsible for your Mandevilla not blooming.
So don’t wait up. Ensure proper food & water for your Mandevilla. Check whether your Mandevilla is getting sunlight or not & other facts that I have listed.
I hope my deep research will come in handy for you. Let me know the results.
Best of luck.