Are you in a new development? Maybe there soil is full of rocks?!? I can't think of another reason why this is happening to your guava.

Is the soil pure sand? This might account for your shrub wilting like this...and then again, it is highly possible it's wilting because of TOO MUCH water.

A newly planted shrub needs a hole that is at least twice the diameter of its root ball (3 times that is better) that has been amended with several inches of good organic material (composted manure, peat moss, compost, etc.). This means the material should have been mixed thoroughly into the soil that was in the hole. The plant needs to be placed in the hole with the soil level of the root ball even with or slightly above the soil level of the surrounding ground. (If it's planted too deeply the feeder roots could be smothering, which will cause the plant to wilt and slowly die.) It should be firmed in, mulched (no mulch means the plant is drying out too quickly), and watered well (once a week is PLENTY, and rain counts). If you did not do this procedure at the time of planting, I would definitely advise you to lift the plant and start over. If you did do this at the time of planting, your plant is likely either suffering from over-watering or some sort of disease.

Thanks guys.

I'm in a 1950's developed area in Lighthouse Point. The soil is sandy, but I would not say "pure sand".

There are lots of plants doing very well in the same area and like I said, I asked about amending the soil at the nursery and was told I did not need to. You'd think they would jump at the chance to sell me compost with even the slightest requirement.

I just went and gave a good tug up on the base of the largest stem and the plant seemed very well anchored. I was looking to see if somehow there had been no root growth. I suppose the feeder root problem you mentioned could be the problem, but as roots have clearly grown out into the soil, is this possible?

Is digging out and re-planting the only way to solve that problem? I'll start by adding more mulch. I'm fairly experienced in planting and made sure the hole was large enough and that the root ball was even with the soil level. The plant is fine...as long as I water it, hence my confusion.

The answer to "too good" drainage is definitely organic material. This is absolutely the only explanation I can think of for a plant continuing to need daily water. I have grown feijoa (this is what you're talking about, right?) and found it to be very undemanding in my well amended and mulched clay soil. I don't ever remember having to water it more than other plants in my garden. If I were you, I would lift the plant and work as many chopped leaves (or peat moss) into the (big) hole as I could. If this doesn't solve the problem, I'll be surprised (and stumped).

Thanks for the information everyone. Turns out I just needed more mulch.

Since the plant was new, I was employing the logic that it needed some space around the stem to make sure the water was staying at the plant when I watered. I mulched up to the base and it's fine. It's a few weeks later now and it's starting to develop new growth, which is what I thought it should have been doing all along - it's a very tolerant and fast growing shrub.