The type of boxes I use are meant to be used together with a grow bag. Grow bags are available in local supermarkets around here. If you are serious about growing organic produce only you should consider the contents of the bag carefully.
Leave the box dry for now:
The self watering boxes have tubes going all the way to the bottom of the box:
A plastic bag can be put into the box to avoid a mess if the box is somehow damaged:
The grow bags have usually been stacked and if you get a bag that has been stored in the bottom of the stack, the soil inside can be quite compact:
Shake the bag thoroughly and loosen the soil, so the roots can develop easily:
Cut three holes in the top with a knife:
Dig out the soil in each of the 3 holes with a small spade and put the soil into a bucket:
Cut three big X’s in the backside of the growing bag:
Fill the three tubes with the soil from your bucket. Only fill the tubes so there’ll be room left to plant the tomato plants. Plant the tomato plants using the remaining soil:
Water a bit on top of each hole. Fill the box with tap water to provide enough calcium for the tomato plants.
Let the water level drop to minimum level regularly to avoid drowning the plants.
The boxes can of course be used for other crops, like cucumbers, bell peppers etc. Take a vacation and let your imagination run wild. Your tomatoes will be safe until you come back 😉