Lemon trees (Citrus limon) provide a mixture of useful and ornamental traits within their showy, creamy fruit and evergreen foliage. They grow best where temperatures remain between 70 F and 90 F, whether outside above U.S. Department of Agriculture plant hardiness zone 9 or inside a temperature-controlled greenhouse. Increasing lemon trees in greenhouses is fairly easy since they need little care once established and will prosper if their moisture, light and temperature requirements are satisfied. But greenhouse-grown lemon trees sometimes develop pest infestations and must be monitored carefully to ensure a decent harvest.
Plant dwarf lemon tree cultivars such as Dwarf Lisbon (C. limon “Dwarf Lisbon”) since they are far smaller than standard lemon trees nevertheless bear similarly large, palatable fruit.
Pot the lemon tree in a 10-gallon nursery container full of a soil mix of equal parts milled peat, loam and coarse sand. Mix in 1 cup of 14-14-14 ratio fertilizer. Stir the soil until the fertilizer is well-integrated. Water thoroughly.
Position the lemon tree near the southern end of the greenhouse at which it will get at least six to eight hours of sunlight each day. Set the tree 1 to 2 feet away from the glass to stop leaf scald.
Position a thermometer 2 feet above the lemon tree to track the temperature. Open the ventilation conduits in the event the fever tops 95 F. Turn on an artificial heat source such as a greenhouse coil if night temperatures fall below 55 F.
Water that the lemon tree whenever the soil feels dry at the top 3 inches. Provide irrigation year-round. Add water until the soil feels fairly moist at the top 5 inches. Lift the pot onto stones or bricks to allow the excess water to drain off.
Decrease water slightly in winter when daylight temperatures are reduced and daylight hours are shorter. Permit the top 5 to 6 inches of soil to dry out. Water when the leaves appear wilted.
Feed the lemon tree with 20-20-20 ratio fertilizer monthly from early spring until late summer. Cease feeding before autumn to impede the lemon tree’s development and allow it to go partly dormant.
Prune off any damaged, crossed or overly long divisions in winter once the tree is partly dormant. Snip off the damaged or crossed branches at their point of origin utilizing clean pruning shears. Trim long divisions to their preferred length.
Watch for light or spotted leaves, which might signal a greenhouse thrip infestation. Harvest the fruit immediately when a thrip infestation is identified. Remove the fruit and discard any with obvious signs of damage.