Achacha leaves turning black at the tips

[Yen]

Hello
I have an achacha tree in a pot facing the sun. It is about a year old. There are new small yellow leaves but many of the existing leaves have black tips and look like they are burnt. What could be happening? too much water, not enough? missing nutrients? parasite?<br /><br />

[pineislander]

They are sensitive to sun when young. I am 1-1/2 years in ground. I planted in open conditions and installed a mini shade house for the trees using 4 stakes with shade cloth stapled on the first year. I planted pigeon pea bushes to make natural overhead shade and then removed the shade cloth. They grow slowly at first. Try to advance them by encouraging growth flushes, once each flush hardens off by adding extra fertility and water. Eventually, they can be put in full sun I have heard that point to be around 60 cm. but exposure should probably be gradual. They can get 25 feet wide. Here is a Bolivian growers guide but it is in Spanish:
https://www.del.org.bo/info/archivos/frutas_exoticas/capitulo%20IX.pdf