I know it's only spring time, but I have lots of little blossoms on my container tomato plants. All are ready to bloom into tomatoes. They often do not reach full size. In fact, I just pulled off four teeny tomatoes that actually tasted great! Sometimes they do not look plump either. Also, should I add coffee grounds to the soil?
To obtain maximum performance with tomatoes:
- When the plants are in bloom, you can facilitate the fruit setting by gently shaking, around noon, the support rods and ropes. This will facilitate the fall of the pollen
- Only start fertilizing once the first fruits have started to swell
- Remove all axillary germinations aside of main branches, which are infertile
- Check that the main branches are supported vertically
- Remove leaves to leave the maximum space to fruits.
The plant needs a soil rich in organic matter and well drained, but also bears fruit if planted on sandy soil or clay.
Following these rules, your tomatoes should be abundant and large.
Since you do not give any information about the place where you are, it is difficult to imagine other possible causes.
In my opinion, add coffee to the ground only serves to make the soil more porous and lightweight, like drainage does. It does not serve as a fertilizer or for other purposes.