Yes, for gardens that charge an entrance fee, payment is typically made directly at the garden entrance. Cash is often preferred.
For the individual gardens within the Open Zoetermeer Garden initiative that require an entrance fee, tickets or payment are almost always handled directly at the garden entrance. There isn't a central ticketing office for all participating gardens.
Visitors should be prepared to pay in cash, as not all private garden owners may have facilities for card payments. It's advisable to carry small denominations if multiple gardens are to be visited. Some events might offer a combined ticket for several gardens, but this is less common for independent private garden openings. Always check the specific event information for payment methods accepted at each location.