Provided herein are adaptors that enable a seed cartridge that is configured to be used with a first type of needle having a locking hub to instead be used with a second type of needle having a cylindrical hub. Such a seed cartridge has a hub at its distal end that is configured to attach to the locking hub of the first type of needle. The adaptor includes a proximal portion configured to removably attach (and in specific embodiments lock) to the hub at the distal end of the seed cartridge. The adaptor also includes a distal portion configured to removably attach to the cylindrical hub of the second type of needle. A central portion of the adaptor connects the proximal and distal portions of the adaptor. A bore extends through the adaptor and allows seeds and optional spacers to be transferred from the seed cartridge into a hollow cannula of the second type of needle. Also provided herein are methods for using such adaptors.