There is nothing nicer than receiving a gift relating to one's passion. If your loved one's passion is gardening, then show your thoughtfulness by giving a gift that will be truly appreciated.
There are so many great gardening gifts that the only constraint is your own budget.
If your budget is small, go for things like gloves, kneepads or even a shady hat. A pretty pot (or a watering-can) filled with a small bag of potting mix, a packet of bulbs, some gloves and a small trowel or other tool will be received with delight by most gardeners. There are many hand tools at hardware stores that are reasonably priced.
If you feel that is too ordinary, how about a subscription to a gardening magazine? A tiny bit more expensive perhaps, but it will give twelve full months of delight. A book on gardening is another idea, but make sure your recipient does not already have the one you choose. Books are often heavily discounted at Christmas time, so you may get a bargain.
On the other hand, a pot that contains a flowering plant is usually a welcomed gift. Be sure to choose a plant that is suited to your climate. Sometimes plants are sent from tropical to temperate zones and kept in artificial conditions in the store. These plants will not do well once taken from their environment. Shrub roses are hardy and attractive and grow in many climates. Tulips do best in the cooler climate.
If your budget is strong, a more expensive tool may be appropriate. A pull-trolley is easier to use than a wheelbarrow and, like some electric tools, is still not terribly expensive. Small electric tools such as whipper-snippers can retail for as little as $20.00. Or if your friend has a hose but not a hose reel, then that would be a more useful gift that he would truly appreciate.
Automatic lawn mowers, electric cultivators, hedge trimmers and brush cutters are in the more expensive price range and you are the only one who can decide whether that is an appropriate gift. However, when the recipient realizes you have given a gift that complements his passion, expensive or not, it will certainly become the best gift your friend has ever received.