Calcium can improve firmness and quality but is poorly absorbed by maturing soft fruit. Most growers know that calcium is important for soft fruit, as it can improve cell wall strength which has a positive effect on shelf life, firmness and ability to withstand diseases. However when you look at the scientific evidence it becomes clear that the calcium applied to crops like strawberries does not always end up in the fruit. Calcium is poorly observed by maturing strawberry fruit therefore a lot of the calcium farmers apply to their crops is wasted as ripening fruit are not able to absorb it.

So why is it the case that calcium absorption is so erratic? Calcium absorption in strawberry fruit is strongly linked to the transport of auxin, a plant hormone. In strawberries auxins in the achene (the seed) are transported into the developing fruit, allowing the fruit to absorb calcium. However ripening is triggered by cessation of auxin transport into the fruit, so as the fruit starts to turn red the ability to absorb calcium rapidly declines.

Red strawberries have very little auxin, and can not absorb any calcium that is applied to them. So when crops are sprayed with foliar calcium, the leaves and green fruit will absorb it, but maturing fruits will not. Usually it is exactly the fruit that can not absorb the calcium that farmers are targeting, in order to improve firmness and post harvest shelf life. This is why results from conventional calcium fertilisers are so erratic, sometimes the fruit can’t absorb calcium into fruit and the input is wasted.