Nitrogen, water, sun, and heat make sugar; but sometimes nothing works. My Mother had a Satsuma mandarin that would not get sweet no matter what we tried; we finally took it out and put in a Washington navel, which produced great oranges; we just had to leave them a little longer on the tree.

You should fertilize your tree a minimum of 3 times a year. However, I dont believe fertilizer is your trees problem. The sugar content (sweetness) of citrus fruits is determined by the number of heat unites the tree receives during the growth season. You do not give your location, so it is difficult to know if your tree is receiving the required amount or not.

Hi Silica
I am in the state of California in LA county area. We don't get enough rain here. I don't think heat is the problem. Thanks.

Fruit quality can be poor if the tree does not get the right balance of potassium, magnesium and calcium. That can be a real problem in alkaline soil.

If your soil is OK then sunlight is the next limiting item. You need about six hours of sunlight or more.

In a cloudy fall I have had trouble getting fruit to sweeten. Fruit can be sour early and sweeten later. The acid may be too high and needs to age so it decreases. "Round oranges" may do this better than tangelos and mandarin types, because they hold their sugar longer.

Okay, everything mentioned above can affect the sugar content of your fruit. However, the most important issue is the time you're picking your fruit. What kind of orange tree is it? Valencias ripen March through July. Navel oranges ripen January through February here in S. Calif. If you're picking a Valencia orange now, they'll be sour. Most mandarins are ripe in the winter, but not all. What types of trees you have would help, amongst all the recommendations offered, previously. If you live in Los Angeles, you have plenty of heat, and we're all assuming the trees are receiving full sun (you don't mention how much sun they are receiving). But, you definitely have not fertilized enough, and timing the picking of your fruit is also pretty important.

Patty S.

We have a tangelo, and lemon tree. The lemons are huge and tasty, while the tangelos are yellow with grapefruit taste and slightly bitter. Don't know when to pick them either in southern MS. They were more bitter last year.