Although Oregon's marine climate is temperate, it isn't quite warm enough to grow lemon trees outdoors year round. However, there is a perfect solution for Oregonians who want to grow lemon trees, and that is to plant lemon trees that can be moved indoors during the winter months. Although standard sized lemon trees are too large for containers, dwarf trees are ideal, and if properly cared for, will produce plenty of full-size fruit.
Keep the container-grown lemon tree outdoors for most of the year. Be sure the tree gets at least six hours of bright sunlight every day, but move it into the shade on hot afternoons.
Allow the soil to dry out slightly between waterings, and then water it deeply until the water drains through the hole in the bottom of the container. Never allow the bottom of the pot to sit in water.
Bring the container-grown lemon tree indoors when the nighttime temperatures drop to 50 degrees. Of all the citrus trees, lemon trees are the most cold-sensitive. Make a gradual transition by putting the tree in a sheltered location on a porch or patio for a few days before you bring it inside.
Be sure the tree continues to get plenty of light, which is more difficult after the plant is moved indoors. Put the plant in direct light, and because Oregon has dark winter days, it's best to use a supplemental grow light for 10 to12 hours each day. Don't put the tree near an open door or window. Too little light and drafty conditions can both cause the tree's leaves to turn yellow and drop off.
Keep the room temperature no higher than 70 degrees during the days during the time that the lemon tree is indoors. At night, the ideal temperature is about 55 degrees.
Feed lemon trees in the spring or early summer, using a fertilizer formulated especially for citrus trees. Feed the tree a second time in late August.
Cut back on water slightly after you bring the tree indoors during fall and winter, but don't let the soil become bone dry. This is the tree's dormant period. Never fertilize during this time.
Move the container-grown lemon tree back outdoors when nighttime temperatures are consistently above 50 degrees. Let the tree become gradually acclimated to its new environment. At first, put the tree in sunlight in the mornings and shade in the afternoons. After a few days, move the tree where it will again get sunlight for at least six hours each day.
Prune as needed to maintain the lemon tree's bushy shape and compact size. Remove any dead branches, and branches that appear weak or spindly. Prune branches that are growing inward or crossing across other branches. Although the lemon tree can be pruned any time, it may be easier to prune it after you've moved it outdoors in the spring.
Re-pot lemon trees in early spring before, right after you notice new growth. However, don't re-pot lemon trees unless they're extremely root bound, because they actually thrive when their roots are somewhat crowded. Move them to a container one size up, and fill the container with good quality commercial potting soil.