Umbrella Thorn Acacia (Vachellia tortilis): Dormant or Dead?

[Sital]

This past spring I started 3 Vachellia tortilis from seed. All 3 sprouted and were doing very well until the "Great Chipmunk Attack of 2021" left only one intact survivor. All through the rest of the summer this little guy grew very nicely and looked green and healthy. Come September/October I brought it inside before the nighttime temperatures dropped below 50F and placed it in front of a window (not south facing unfortunately) with a grow light.

Almost immediately, the leaves began to drop off and within a few weeks it was completely bare. It's been in bonsai soil (from Bonsai Supply) the entire time and I don't believe watering is the issue. I've read that some acacia species can be deciduous, but I'm not sure about Vachellia tortilis.

So what's the verdict: deciduous/dormant or dead?

Thanks.

 

[Divide_by_zero]

I have no experience with this species but one source I found does say "Plants older than 2 years have been observed to be somewhat frost resistant. Vachellia tortilis occurs in deciduous woodland, thornveld and bushveld. It is found from sand dunes and rocky scarps to alluvial valley bottoms, avoiding seasonally waterlogged sites." So I would say it may be just dormant caused by the sudden change in light. Have you done a scratch test to see if the cambium layer is still green?

One individual who does have an Acacia in his collection and may have more info is Nigel Saunders ("Bonzai Zone" on YouTube). I'm not sure whether he is on here or not.

 

[Sital]

Thanks for the reply. I do watch Nigel's videos and I seem to recall him mentioning the leaves dropping. The scratch test does show bright green so maybe I'll just put this one in my attached garage with my other deciduous trees for the winter.

 

[SWfloirda]

I’ve got rabbits foot acacia or Vachellia cornigera, also sweet acacia Vachellia farnesiana. The sweet acacia keeps all of its leaves through the winter. The rabbits foot has lost about half and doesnt look great. But I keep mine outside, so a totally different experience.
Many tropicals are semi deciduous all I can do is wait for spring and hope for the best.

 

[sorce]

Welcome to Crazy!

I'd ask @YukiShiro or @fredman .

Acaskayou a question.

Sorce

 

[fredman]

Yeah if there's green, it's sleeping. They very quickly loose the leaves come winter. They are very tough trees found throughout Africa.
Just keep it barely moist during winter...it'll smile at you come spring.
Does it have thorns yet?

 

[Sital]

Yeah if there's green, it's sleeping. They very quickly loose the leaves come winter. They are very tough trees found throughout Africa.
Just keep it barely moist during winter...it'll smile at you come spring.
Does it have thorns yet?

I planted the seeds at the end of April, and while I don't remember exactly when the thorns came, it was probably somewhere around the beginning of summer.

 

[fredman]

I planted the seeds at the end of April, and while I don't remember exactly when the thorns came, it was probably somewhere around the beginning of summer.

Ah lovely....love the thorns. Love the tree. To me it's the symbol of Africa....the umbrella trees on the savanna.
Quite an unusual arrangement of thorns on Tortillis...one is straight and also a curved one. .
They're called "haak en steek" (hook and prick) in South Africa.
Can I ask you for a photo of it plz.

 

[YukiShiro]

This past spring I started 3 Vachellia tortilis from seed. All 3 sprouted and were doing very well until the "Great Chipmunk Attack of 2021" left only one intact survivor. All through the rest of the summer this little guy grew very nicely and looked green and healthy. Come September/October I brought it inside before the nighttime temperatures dropped below 50F and placed it in front of a window (not south facing unfortunately) with a grow light.

Almost immediately, the leaves began to drop off and within a few weeks it was completely bare. It's been in bonsai soil (from Bonsai Supply) the entire time and I don't believe watering is the issue. I've read that some acacia species can be deciduous, but I'm not sure about Vachellia tortilis.

So what's the verdict: deciduous/dormant or dead?

Thanks.

I concur with Fredman

your tree is dormant, tortilis only grows in our dryer hotter parts, so it reacting to cold( relatively speaking) by dropping all it's leaves is totally normal for it in you climes.

I would however take it away from the window and place it in a more sheltered spot. The spot in front of the window(not south facing) might be colder than the rest of the house at night....also it does not need any sun or light atm.
I grew up in a town that went down to -12 celcius in winter, used to keep a lot of acacias that cannot handle those temps. Just before the cold set in I would place them in a spot away from any windows and water only once I felt the soil dry out about an inch underneath the surface, never lost any of them

Best regards
Herman

 

[fredman]

Just before the cold set in I would place them in a spot away from any windows and water only once I felt the soil dry out about an inch underneath the surface, never lost any of them

Like in the kitchen...?
(Sorry couldn't resist)
Herman how do you water your Acacias in winter?

 

[YukiShiro]

Like in the kitchen...?
(Sorry couldn't resist)
Herman how do you water your Acacias in winter?

Kitchen is the best place!!!

when I stayed in the highveld I just checked on them every few days and pushed my finger into the soil, if it's dry 1 inch underneath the surface, I would water.

where I am now all my trees live outside except my baobabs. the few acacia that came with to the new place love the winter temps so much that they do not drop their leaves so I defoliate them when my jap maples drop their leaves.
Acacia's needs some sleep too, they just grow better in spring when I defoliate in late autumn.

Best regards
Herman

 

[fredman]

Ah lovely...sounds like you're in the lowveld now..?

 

[Sital]

I concur with Fredman

your tree is dormant, tortilis only grows in our dryer hotter parts, so it reacting to cold( relatively speaking) by dropping all it's leaves is totally normal for it in you climes.

I would however take it away from the window and place it in a more sheltered spot. The spot in front of the window(not south facing) might be colder than the rest of the house at night....also it does not need any sun or light atm.
I grew up in a town that went down to -12 celcius in winter, used to keep a lot of acacias that cannot handle those temps. Just before the cold set in I would place them in a spot away from any windows and water only once I felt the soil dry out about an inch underneath the surface, never lost any of them

Best regards
Herman

Thanks for the reply. I only had them by the window because I have a table there for the winter with my other tropicals. I needed more room on the table anyway, so I have moved them away from the window.

 

[Orion_metalhead]

My acacia grows indoors under lights. Overwatering is usually the biggest concern.

 

[YukiShiro]

Ah lovely...sounds like you're in the lowveld now..?

I moved to the Pierre van Ryneveld suburb in Centurion

coldest for the two years I've lived here was 0 Celcius....so no worries about it being to cold out for my thorns or figs xD

lekker
Herman

 

[YukiShiro]

My acacia grows indoors under lights. Overwatering is usually the biggest concern.

sup man,

you never take them outside?

Best regards
Herman

 

[Sital]

My acacia grows indoors under lights. Overwatering is usually the biggest concern.

I really don't think it's a watering issue as I am careful about watering only when the trees need it, not on a schedule. It was doing really well all summer, and the leaf drop seems too coincidental with falling temperatures/bringing it inside.

 

[Orion_metalhead]

sup man,

you never take them outside?

Best regards
Herman

Outside in spring through fall.

 

[YukiShiro]

Outside in spring through fall.

Interesting, do they drop their leaves in fall and then flush out again after they move indoors under the grow lights?

best regards
Herman

 

[YukiShiro]

Just to be clear:

I'm really interested,
as the norm in South Africa is to give them rest in the non-growing season, by defoliating them in autumn, to promote vigor in the growing season.
This might be myth or not...
want to know if you've noticed anything in particular, and how the tree acts during the off season. When you place it under grow lights.

always up for learning and figuring out new stuff

Best regards
Herman