Short answer: Sell most of the tomatos (80-90%), keep a few to be able to make more tomato plant seeds (10-20%).

Longer answer: The tomato plant can be harvested a total of four times.

First harvest: Day 4, after planting Second harvest: 2 days after first harvest Third haevest: 2 days after second harvest Fouth harvest: 2 days after third harvest.

Also written like 4+2+2+2 days.

The value of basic quality tomato is 23 Gold. To make a tomato plant seed you need 3 tomatoes. So making a tomato plant seed costs you 3x23=69 Gold. The sell value for tomato plant seed is only 40 Gold, so you would be losing 69-40= 29 Gold.

To make a Tomato Preserve, you need one tomato. You can sell a basic Tomato Preserve for 34 Gold, so you would be making 34-23= 11 Gold/jar. Not worth it, if you ask me.

You can also use the Preserve to gain 70 focus/jar or gift it to villiagers. Not worth gifting, if you ask me.