Too much water. Once, maybe twice, a week max - depending on the weather.

Ummm. How often you water also depends upon the size of the pot. If on the small side for the plant, will need far more often than 1/week.

A moisture meter at Lowes is cheap--I got one because I always have trouble determining when to water. Worth it's weight in gold having one.

It also depends on the soil. Most of my potted plants get watered every other day if it doesn't rain. My soil is very porous and doesn't hold water well. This is better for over all health of the plant.

You say tomato TIPS, so are you talking about an area of black at the blossom end of the fruits? If so, then the problem is BER ( blossom end rot) which can be a real problem with container grown tomato plants, as well as with those grown inground.

If it's BER please go to the top of this first page, click on the FAQ link and scroll down until you come to the article about BER.

You can also go to Google IMAGES and type in something like tomato BER or spell it out and take a look at some pictures to see what I'm talkiong about.

Carolyn