Swedish to English Science Agriculture Horticulture

"Behandling av stubbar kan utföras hela året med undantag av savningsperioden."

I've spoken to a horticulturist in Sweden who informs me that the 'savningsperiod' is in the spring, and is when sap is rising through the tree. If the tree is badly damaged, it can result in the tree 'bleeding' to death almost, as it loses its sap.

I have struggled to find a term in English better than 'sap period' which returns no hits on google, so I would appreciate your input! Thank you in advance.