randi_holbrook

What is wrong with my Mandevilla?

Randi Holbrook
September 7, 2019
last modified: September 7, 2019

Got it about 3 weeks ago. Gets only dappled sun. The front of it looks decent, but the BACK! Attaching pics of both front and back. Some leaves dry and almost crispy, some brown, and some perfectly normal looking. I've started watering it more often, as what I read seemed to indicate it might be underwatered. But no change.


Comments (20)

  • Randi Holbrook


    Okay, it wouldn't insert the pic of the BACK of the plant, which looks terrible. Let me try again.

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  • floral_uk z.8/9 SW UK

    The pictures are not clear enough to see any detail. Could you put your plant in a good light against a plain background and try again?

    If it lives in that corner it looks far too dark for a Mandevilla survive. They need lots of light. It already looks as if it's starting to etiolated.

  • PRO
    tapla

    Hi, Randi. Was it exposed to direct sunlight for more than an hour? It looks like sunburn, but sometimes the leaves coming in contact with something topically phytotoxic (damaging to leaf surfaces) can produce these symptoms. The fact that one side (the sunny side?) is more affected than the other tends to lend some additional credence to the potentiality of sunburn.

    Are you checking moisture levels with a "tell"?

    Al

  • grrr4200

    Severe lack of loght

  • Randi Holbrook

    Not exposed to sunlight here, only dappled, but might have been before I got it? Although it looked fine when I bought it. Forgot to mention it was not super close, but close, to a register for the air conditioning, and that was the side that was near it.

  • Matt z5b GH 9b

    It looks like a dip. It needs some sun. is this another you keep inside?

  • Randi Holbrook

    Yes, I keep it inside. And it was labeled Mandevilla, but we all know how accurate Lowe's is with their labels!

  • PRO
    tapla

    That type of damage doesn't occur from lack of light, and if it was overexposed to light prior to you acquiring it, you would have noticed the problem right away - within a day ...... and the damage would have had to happen the day or day before you acquired it for it to not be conspicuous when you purchased it. It was very likely due to the dry air from the air conditioning or chill injury, which can happen at temperatures in the 50s if the temperature change is sudden.

    Any chance you made a stop or two on the way home and left it in a hot vehicle?

    Al

  • Randi Holbrook

    Right, Al. I didn't notice the damage until I'd had it probably almost a week. No, I never make a stop on the way home after buying plants. They are ALWAYS the last stop. It's looking worse by the day, and I don't know how often I should water it. Some say keep moist, and others say let dry out. I didn't notice any improvement after watering it, so I'm assuming I'm not underwatering.

  • PRO
    tapla

    Try using a tell and withholding water until it comes out nearly dry. Something I wrote to explain:

    Using a 'tell'

    Over-watering saps vitality and is one of the most common plant assassins, so learning to avoid it is worth the small effort. Plants make and store their own energy source – photosynthate - (sugar/glucose). Functioning roots need energy to drive their metabolic processes, and in order to get it, they use oxygen to burn (oxidize) their food. From this, we can see that terrestrial plants need air (oxygen) in the soil to drive root function. Many off-the-shelf soils hold too much water and not enough air to support good root health, which is a prerequisite to a healthy plant. Watering in small sips leads to a build-up of dissolved solids (salts) in the soil, which limits a plant's ability to absorb water – so watering in sips simply moves us to the other horn of a dilemma. It creates another problem that requires resolution. Better, would be to simply adopt a soil that drains well enough to allow watering to beyond the saturation point, so we're flushing the soil of accumulating dissolved solids whenever we water; this, w/o the plant being forced to pay a tax in the form of reduced vitality, due to prolong periods of soil saturation. Sometimes, though, that's not a course we can immediately steer, which makes controlling how often we water a very important factor.

    In many cases, we can judge whether or not a planting needs watering by hefting the pot. This is especially true if the pot is made from light material, like plastic, but doesn't work (as) well when the pot is made from heavier material, like clay, or when the size/weight of the pot precludes grabbing it with one hand to judge its weight and gauge the need for water.

    Fingers stuck an inch or two into the soil work ok for shallow pots, but not for deep pots. Deep pots might have 3 or more inches of soil that feels totally dry, while the lower several inches of the soil is 100% saturated. Obviously, the lack of oxygen in the root zone situation can wreak havoc with root health and cause the loss of a very notable measure of your plant's potential. Inexpensive watering meters don't even measure moisture levels, they measure electrical conductivity. Clean the tip and insert it into a cup of distilled water and witness the fact it reads 'DRY'.

    One of the most reliable methods of checking a planting's need for water is using a 'tell'. You can use a bamboo skewer in a pinch, but a wooden dowel rod of about 5/16” (75-85mm) would work better. They usually come 48” (120cm) long and can usually be cut in half and serve as a pair. Sharpen all 4 ends in a pencil sharpener and slightly blunt the tip so it's about the diameter of the head on a straight pin. Push the wooden tell deep into the soil. Don't worry, it won't harm the root system. If the plant is quite root-bound, you might need to try several places until you find one where you can push it all the way to the pot's bottom. Leave it a few seconds, then withdraw it and inspect the tip for moisture. For most plantings, withhold water until the tell comes out dry or nearly so. If you see signs of wilting, adjust the interval between waterings so drought stress isn't a recurring issue.


    Al

  • Randi Holbrook

    What's weird is, half of some of the leaves are brown, the other half of the leaf being green. None of my plants have done this before. Thank you, Al, for explaining. I know the roots need oxygen, but have read about Mandevillas in the past where they said they like to be kept moist, and to never let them dry all the way out. I did that with my first one, and it was very happy. This plant is in the exact same spot (dappled sun) and I watered it the same way, with drastically different results from what I got with the first plant. Now I'm suspecting the soil. It doesn't appear light enough to me. It drains fairly fast, but doesn't look like what I normally use (cactus/perlite 50/50). I feel if I repot it now, I might kill it. It's already on very shaky ground. It's been moved further away from the air vent, and in a little more sun, but not much. Do you recommend using Pro-Tekt? How about Superthrive? I really wanted this Mandevilla, as I so enjoyed the last one's yellow blooms. They are my favorite.

  • PRO
    tapla

    Surrounding each leaf is what's called a boundary layer of still air. The air serves to protect the leaf from water loss, but it's also a good insulator, which isn't always a good thing. Sometimes it traps heat inside the boundary layer and causes the plant to over-heat in still; air conditions, such as indoors; but I'm off the track here. In the case of multiple leaves in close proximity, such as occurs more toward the center of the plant, rather than the still area of air surrounding a single leaf, the boundary layers of ALL leaves combine to form sort of a collective boundary layer. IOW, the leaves and leaf surfaces toward the center of the plant get more protection from the dry/cold air being emitted from air ducts than leaves at the perimeter of the leaf mass. This is why 2 blankets are warmer than 1. 2 blankets or layers of clothing are better at insulating against loss of heat because the boundary layer of air trapped in the fibers of the blankets or sweatshirt disallow exchange of cold air for warm. Some plants mimic the effects of a blanket by producing tiny hair-like trichomes that emerge from the leaf/stem surface. trapping still air and further insulating the plant from water loss and rapid temperature shifts. I'm guessing the worst damage to leaves occurred where the part of the damaged leaf was somewhat isolated from the collective protection afforded by a group of leaves in close proximity??

    As an aside, most plants can adjust to/tolerate the photo load associated with full sun pouring through windows, but many can't tolerate the passive heat gain in leaves that direct sun creates. Turning on a fan disrupts the boundary layer and facilitated heat loss into the surrounding air, allowing plants to tolerate much more direct sun that they could otherwise.


    Now I'm suspecting the soil. It doesn't appear light enough to me. It drains fairly fast, but doesn't look like what I normally use (cactus/perlite 50/50). I feel if I repot it now, I might kill it. It's already on very shaky ground. It's been moved further away from the air vent, and in a little more sun, but not much. Repotting is probably not a good idea at this time, but you can pot up with the plant experiencing little if any stress. Potting up allows you the option of using ballast to eliminate nearly ALL of the excess water the soil can hold. If you're unfamiliar with using ballast, Read This. Do you recommend using Pro-Tekt? Yes. It contains opalescent silicon, which the plant is able to actually take up. Sand is nearly all silicon, but a plant planted in sand will almost always have lower silicon levels than plants planted out in garden soil. It only works if you use it religiously. Like calcium, it must be present in the nutrient stream at all times to be effective, but it really does work to limit stress from several quarters. Heat, chill, herbivory (damage from things that eat plants or plant sap), excessive or inadequate moisture levels, pathogens, and other I probably neglected. Most plants grown in containers contain much less silicon than plants grown out (in the landscape). How about Superthrive? The question comes up so often I wrote something about it. See just below.

    Superthrive or Superjive

    The question regarding the value of Superthrive as a miracle tonic for plants is often bandied about in horticultural circles. Over the years, I had read claims that ranged from, “I put it on my plant, which had never bloomed, and it was in full bloom the next day.” to, “It was dead - I put Superthrive on it and the next day it was alive and beautiful, growing better than it ever had before.” I decided to find out for myself.

    If you look for information on the net, you will probably only find the manufacturer’s claims and anecdotal observations, both so in want of anything that resembles a control. Though my experiments were far from purely scientific, I tried to keep some loose controls in place so that I could make a fair judgment of its value, based my own observations. Here is what I did, what I found, and the conclusions I made about any value the product Superthrive might hold for me.

    On four separate occasions, I took multiple cuttings of plants in four different genera. In each case the group of cuttings were taken from the same individual plant to reduce genetic variance. The plant materials I used were: Ficus benjamina, (a tropical weeping fig) Luna apiculata (Peruvian myrtle), Chaenorrhinum minus (a dwarf snapdragon), and an unknown variety of Coleus. In each instance, I prepared cuttings from the same plant and inserted them in a very fast, sterile soil. The containers containing half of the cuttings were immersed/soaked in a Superthrive solution of approximately 1/2 tsp per gallon of water to the upper soil line. The other half of the cuttings were watered in with water only. In subsequent waterings, I would water the “Superthrive batch” of cuttings with a solution of 10 drops per gallon and the others with only water. The same fertilizer regimen was followed on both groups of cuttings. In all four instances, the cuttings that I used Superthrive on rooted and showed new growth first. For this reason, it follows that they would naturally exhibit better development, though I could see no difference in overall vitality, once rooted. I can also say that a slightly higher percentage of cuttings rooted that were treated with the Superthrive treatment at the outset. I suspect that is directly related to the effects of the auxin in Superthrive hastening initiation of root primordia before potential vascular connections were destroyed by rot causing organisms.

    In particular, something I looked for because of my affinity for a compact form in plants was branch (stem) extension. (The writer is a bonsai practitioner.) Though the cuttings treated with Superthrive rooted sooner, they exhibited the same amount of branch extension. In other words, internode length was approximately equal and no difference in leaf size was noted.

    As a second part to each of my “experiments”, I divided the group of cuttings that had not been treated with Superthrive into two groups. One of the groups remained on the water/fertilizer only program, while the other group was treated to an additional 10 drops of Superthrive in each gallon of fertilizer solution. Again, the fertilizer regimen was the same for both groups. By summer’s end, I could detect no difference in bio-mass or vitality between the two groups of plants.

    Since I replicated the above experiment in four different trials, using four different plant materials, I am quite comfortable in drawing some conclusions as they apply to me and my growing habits or abilities. First, and based on my observations, I have concluded that Superthrive does hold value for me as a rooting aid, or stimulant if you prefer. I regularly soak the soil, usually overnight, of my newly root-pruned and often bare-rooted repots in a solution of 1/2 tsp Superthrive per gallon of water. Second, and also based on my observations, I no longer bother with its use at any time other than at repotting. No evidence was accumulated through the 4 trials to convince me that Superthrive was of any value as a “tonic” for plants with roots that were beyond the initiation or recovery stage.

    Interestingly, the first ingredient listed as being beneficial to plants on the Superthrive label is vitamin B-1 (or thiamine). Growing plants are able to synthesize their own vitamin B-1 as do many of the fungi and bacteria having relationships with plant roots, so it's extremely doubtful that vitamin B-1 could be deficient in soils or that a growing plant could exhibit a vitamin B-1 deficiency.

    Some will note that I used more of the product than suggested on the container. I wanted to see if any unwanted effects surfaced as well as trying to be sure there was ample opportunity for clear delineation between the groups. I suspect that if a more dilute solution was used, the difference between groups would have been even less clear.

    It might be worth noting that since the product contains the growth regulator (hormone) auxin, its overuse can cause defoliation, at least in dicots. The broad-leaf weed killer Weed-B-Gone and the infamous “Agent Orange“, a defoliant that saw widespread use in Viet Nam, are little more than synthetic auxin.


    Al

    Randi Holbrook thanked tapla
  • Randi Holbrook

    Thank you SO MUCH, Al, for taking the time to explain things in detail. I'm not sure if the leaves affected were isolated from the collective protection. The ones I see now that are half green and half brown don't seem any more isolated than most of the rest of the plant. Most of the leaves were ALL brown near the bottom of the plant, and I removed the ones that were dry, crackly, and ready to fall off anyway. The plant is a lot more narrow and much thinner now, of course.


    I didn't know Pro-Teck was actually beneficial, so I will use it on this plant until it recovers (if it does). I had read about Superthrive being controversial, and I see now that it is really only helpful when rooting and in newly potted repots. So if I repot this one after reading the link you gave, I will use it.


    I am going to read the link about ballast now. I sure hope this plant comes around for me, and I feel like I'm at least doing SOMETHING for it's good, after reading your posts. Thank you again--you have been incredibly helpful.

  • PRO
    tapla

    ..... my pleasure.

    Al

  • floral_uk z.8/9 SW UK

    Whatever else might be troubling it, I still think it lacks light, not because I can see brown leaves but because the new stems appear to be pale and with excess legth between nodes, even for a vine. It looks as if it is being kept on a bathroom counter which is unlikely to be in a bright enough position for this subject.

    Randi Holbrook thanked floral_uk z.8/9 SW UK
  • Randi Holbrook

    No, I only put it on the bathroom counter to take the pics. It stays near windowsill on a plant stand with my other plants, It gets dappled sun, but I moved it slightly today so it gets a bit more.

  • floral_uk z.8/9 SW UK

    I see. That explains the gloom. I think moving it into more light will help.

    Randi Holbrook thanked floral_uk z.8/9 SW UK
  • hc mcdole

    If you want it to bloom, it needs full sun. Getting a little late this year to do that. Acclimate it to sun next year (if it survives) or you can see what you can eke out the remainder of the growing season. The big Alice DuPont mandevilla plants are usually planted on mailbox posts in full sun around here. I haven't seen them planted this way in a few years though - guess folks got tired of buying a new one each year?


    Home Depot back in May this year


    The only one I grow now is Dipladenia (Mandevilla) 'Stars and Stripes' in its 8th year doesn't bloom like it did when new but I figure it needs even more sun year round. If only I had a greenhouse to keep it this healthy all year long.


    Aug 29, 2019 - Stars and Stripes finally blooming after hot full sun all summer long.




    How it looked in 2011 when first bought, probably grown in Florida and retailed at Walmart.



    A red one I had in 2017 - full sun with moss rose planted in same container. I lost it when I left it outside too long in late fall freezes.


    Whatever you do, watch out for vines looking for light like it did in a small utility room for winter. The vines grew into the cords of the pulled up mini-blinds. This was May 2, 2013



    and this was in Jan 31, 2013


    You could just grow it as an annual too.

    Randi Holbrook thanked hc mcdole
  • Randi Holbrook

    What beautiful pics of Mandevillas! The one I had before would bloom for me, and it was in the same place this one is. I don't understand that. Things get burned here in the desert like you wouldn't believe. That is why most plants in my house have partial shade. I have to be careful, even with plants that want full sun.

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