Answer: Strawberries are sweetest if you let them get completely red before harvesting them. I have grown strawberries in Texas and noticed the following five factors which contribute to berry size:
Pollination - A single strawberry is composed of a group of seeds and surrounding flesh. When a seed is pollinated the flesh around it grows larger. Therefore, the better the pollination the larger the berry.
Plant Size and Health - The larger the plant and the more healthy and numerous the leaves, the more carbohydrates it can produce and the larger and sweeter the fruit.
Variety - Some varieties are just naturally larger than others. Also, some will be better adapted to a particular area.
Cluster Position - The first blossom to open in the cluster is the one at the end of the cluster, known as the "king" berry. It will be larger than the secondary berries in the cluster. There are sometimes even tertiary berries in the same cluster which are smaller still.
Part of the Season - The early berries (February and March) tend to be larger than late season fruit (late April to May).
Hope this helps!
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