Topping a tamarillo tree, second main branch does not grow

[alejandrov]

Hi everyone!

I have a tamarillo tree that I grew from seed, but there is some problem with it when it comes to topping/pruning. I topped it when it had around 50cm in height so that it would have two main branches and it all went well, but in a couple of weeks one branch became growing quicker than the other and the other one stopped growing at all having just a couple of centimeters. Eventually leaves on the shortest branch started dying by going yellow.

After that I decided to top the largest branch again, but in a couple of weeks the smaller branch started growing quicker and overdid it. Now the other branch is not growing again at all.

What can it be? I'd like it to have two main branches, but can't make it work as only one's progressing. I'm in Argentina, the spring is about to begin over here and I'd like to point out that I was feeding it a couple of times during the winter. Thanks a lot and best regards everyone!

[CeeJey]

Somebody correct me if I'm wrong but this sounds like apical dominance: https://en.wikipedia.org/wiki/Apical_dominance. Basically in plants that exhibit strong apical dominance, hormones in the dominant main branch/central stem keep lower branches from growing much (think sunflowers that grow up and barely to the sides at all). If so, you can only have one dominant leader branch growing at one time, probably (because it's turning off growth on lower side branches).

I've not grown tamarillos so I don't know first-hand, but it sounds like that behavior. Looking at pictures of young tamarillos on Google they seem to exhibit that same sunflower-like up-but-not-out behavior when they're small. Again though, this is just an educated guess. 

EDIT:I know a lot of trees with strong apical dominance, if you trim the leader they will grow out lower for a bushier plant, but not everything does that. Some of them (silk floss, off the top of my head) shoot upwards from a side branch like this, or act oddly (jujubes).

[Vegan Potato Man]

I'd suggest low stress training if youre able to bend the stem enough.

It should break the apical dominance enough to give you more even branches.

You'll need something to tie both branches to.

[shitflipper]

I think that the reason you aren't having success with topping the plant is because it is next to a windowsill. Only the branch next to the windowsill will grow out because it is next to the sun. Maybe try rotating the plant and see what happens. Though, it might be too late already (you could have to top it again then try rotating it around).

Low stress training like someone else mentioned might work, but I'd be worried about the branches breaking under the weight of fruit. If it's an indoor plant it probably won't fruit heavily enough for the branches to break though.

If you end up topping it again, make sure to root the cutting for an even lower bearing plant.

[Plantinyum]

I had the same experience with tamarillo, only with the young plants thought ,once they had their first iflorescence they started branching out and forming nice canopies. For me they awlays branched at the spot where they had flowers. They like to have some heigh before they start branching, mine also were just growing with a solo stem, i pinched the top and had 2 to 3 branches coming out of the spot.
Light will make it branch out better, right now the plant is lacking light so its investing all its energy into one growing point in order to reach the light source faster, theres no point for it to branch out and create leaves, which will be in a shade condition.

[alejandrov]

Thanks for your replies, everyone! I think the last two answers hit the spot as the plant was near the window during the whole winter to protect it from strong winds and cold weather. Since it's almost spring over here, I will take it outside in a couple of days or so.

And yes, I had to top it once again so hopefully the two main branches will grow now as it will have more sun. I don't really think the LST will work as the trunk and branches are very easy to break and not too pliable. A couple of questions below.

1. How often should I feed it considering that it's springtime?

2. Does the trunk looks okay? Should it be thicker and stronger?

3. I have a small tamarillo seedling in a tiny pot now, ready to repot. The big plant is in a 35 liter pot, should I go for something bigger with the other plant?

4. When do you recommend topping the small plant? When it's 30 cms or so?

Thanks a lot and have a great weekend, everyone!

[Plantinyum]

To your questions regarding growing....
U can feed them quite a bit, they are not verry sensitive to ferts in my experience, just follow the rates on the fert u will use. I kinda neglected mine this year and havent fertilized them at all ,they are growing nicely thought ,in pots.

The trunk should be ok, it grows proportionally with the rest of the plant ,it should thicken up when u put it outside and it starts growing strong in the sun.dunno what is going on with the leaves though, it looks like u may have a pest of some sort, the curved inward way they look it not normal, it may be from the light also....

For the repotting, u should repot it only if you see alot of roots around the perrimeter of the soil  or down at the drainage holes. You will know that it needs repotting when u have to water it every day like i did last year. I usually check for the need of repotting by taking the plant out of the pot and inspecting the roots, dunno if thats possiblein your case and its also kinda dangerous since if not the soil around the roots could just collapse, so be warned !