My guava plant is producing sour fruit. Is this because of a nutrient deficiency or because of the type of plant? How can I grow sweet guava fruit?
It is "Sour Guava". It is called "Cas" in Costa Rica. You can make the most delicious drink in the world with it. I always wanted to know if I could buy "Cas" in the U.S. so I researched it a few years back and found that its name in english is "Sour Guava" of course it was all imported and $25 a pound. Super rare stuff outside of central america, Cas is in decline in Costa Rica too... Something environmental. Anyhow enjoy your tree and take care of it.
While I have never grown guava and I know very little about it, I can take a guess:
Maybe it's the light, moisture and/or temperature. I eat sempervivum leaves on occasion. I notice that when it's been hot, dry and sunny for a while, they tend to taste like malic acid (the stuff in green apples that makes them sour). When it's been cooler and not as sunny for a while, they're not very acidic.
Anyway, it could be that your plant is stressed. I know stress causes some plants to produce more chemicals (like it makes hot peppers hotter). It's possible that a stressed guava would be more sour. It's also possible that it's not getting enough sunlight. I heard a rumor that sunlight helps fruit to be sweeter.
It could also just be unripe.
Remember, though, I haven't studied or grown guava, yet.
Edit: Upon some investigation, Wikipedia says that guava fruit may be sweet or sour. It does not say if some varieties are sour when ripe, however. I saw a site that talks about sour guava as if it's a variety of guava. I also saw one site that said green guava are much firmer and sour, while yellow guava (or yellow with a pinkish tinge) are ripe and sweet. Most people seem to be of the opinion that guava are just not sour. So, it's possible that there are either only some varieties that can get sour, and they're less common, or else some people referred to astringent as sour (some people actually do that; so, I consider this a good possibility).
I have Psidium guajava seedlings growing not 3 years old. They were well watered and fertilised with good looking fruit. However they are very sour. I have one self sown seedling that is a wildling that was never watered, but gave the most sweet and tasty fruit. Sometimes a first crop can be poor so I will wait until next year's crop to see what is really going on with the sour ones