Assign Taxonomy Based on Custom Field Value

/**
 * Programmatically assign taxonomy term by custom fields
 * 
 * @param int $post_id
 */
function rd_assign_taxonomies($post_id) {

    if (get_post_type($post_id) == 'vegetables') {
        $terms = array();

        // Here we'd check to see if the post has the specific fields, and if so add the IDs or slugs of the taxonomy terms to the $terms array
        // The exact details will depend on how the checkboxes were implemented, for example as native postmeta or ACF fields

        wp_set_object_terms( $post_id, $terms, 'seasons', false );
    }
}

add_action('save_post', 'rd_assign_taxonomies');