Gifting
Seeds, sprouts and adult flowers can be gifted to other users. When gifting seeds the receiver needs to have a free seed-slot. You can find the gift-link on the detailed flower-page. At every update/refresh of  the page a new code is provided, which is afterwards valid for 24 hours. If the receiver of the gift is not able to accept the flower within that time a new code has to be sent. 
Gifting a flower is quite easy. To deliver the code to the receiver you can sent it either by PM on any forum, post it on a forum thread or even sent it by email. Albeit plants were not meant as trading goods in Flowergame in the first place a trading section was set up on the Flowergame-forum
Adoption
Adoption is one option of gifting. Basically it is assumed that a gifted flower is not regifted or even traded by the receiver. The Flower adoption center-thread on the Flowergame-forum was created especially for this purpose. Other threads opened up by the users have similar opjectives. 
Trading
In Theo Trading-section of the Flowergame-forum various trading-requests are posted. Trading is a mutual gifting-agreement. There is no guarantee for a correct transaction. However, the spirit of friendship and mutual trust are very important for the Flowergame community. All the players do their best to keep the game as it is now: informal, without unnecessary rules, and based on mutual honesty. Ultimately, the flowers are nothing more than a way to spread joy.