Not at all—if you choose the right setup, growing a small lemon tree in an urban planter box is a realistic and rewarding project. The key is to work with the tree’s needs rather than fighting them. Start with a dwarf or semi-dwarf variety such as Improved Meyer, dwarf Eureka, or dwarf Lisbon. These stay more manageable in containers and are far easier to move, prune, and protect than a full-size tree.
Use the largest planter box you can reasonably fit—ideally at least 18–24 inches wide and deep, with a volume around 15–20 gallons (45–75 liters). Drainage is non-negotiable: drill holes if needed, add a saucer or wheeled base, and fill with a well-draining potting mix rather than heavy garden soil. A slightly acidic citrus mix works well. Position the box where the tree receives at least 6–8 hours of direct sun; balconies, rooftops, and sunny courtyards can work, but reflected heat from walls may dry the tree faster.
Water when the top 2 inches of soil feel dry, then water thoroughly until it drains. Never let the roots sit in water. Feed with a citrus fertilizer during the growing season, prune lightly to shape the tree and remove dead or crossing branches, and repot every two to three years. In cold climates, move the planter indoors or into a protected spot before temperatures drop near freezing; container roots are more vulnerable than roots in the ground. If flowers appear indoors, hand-pollinate with a small brush to improve fruit set.
Expect a modest harvest rather than an orchard-sized crop. A healthy dwarf lemon in a good planter can produce a handful to several dozen fruits once established, depending on light, variety, and care. Watch for pests such as scale, spider mites, and aphids, and inspect leaves regularly. In short, it is not asking too much—it is asking for the right variety, a large drained container, strong sunlight, consistent watering, and a little winter protection.