My wife has had success starting an avocado from seed. It grew fast. But now the leaves are starting to turn brown. (See photos.) Any ideas why this is happening? I'm thinking it may be time to put into a larger pot, but that may be a separate matter. (Looking for advice here too: what size pot should I put it in so I am not transplanting every year?) I don't think avocado roots go deep, so am planning to put it into a pot that is wide, but shallow. And does it need plant food?
An update. 1) This Spring, I moved the plant to a larger pot, and gave it some plant food (16-10-10 container food, if I remember correctly). 2) Also, I read somewhere that Avocado plants like humidity, so I put a big clear garbage bag over the plant in early Spring. When the weather got warmer, I bought a sprinkler bottle from The Dollar Store and gave the plant a sprinkling every day that was clear and sunny. 3) When nights stayed warmer than 12 degrees Celcius, the plant stayed outside all day, so it got plenty of direct sunshine. End result for the summer: the plant added new bright green growth.
Your avocado looks great! But you don't have to be so overly careful with your tree. Avocados can easily take even light frosts without any damages. Young leaves are very tender though, so better avoid late frosts.
There's a big difference between 'deep' in the ground (roots growing half a metre down, rather than 3 metres), and 'deep' in a pot (10 cm deep, rather than 30 cm deep)! Greater pot depth will give it better moisture and nutrient holding capacity.