1. Understand the light and temperature requirements of citrus – Citrus trees need 8 hours of sun. A sunny, wind-free location is ideal. Citrus trees are very frost-sensitive and must be protected or moved inside to a covered area in cold weather. Kumquat and Mandarin trees are most cold-hardy followed by grapefruit and orange. On the other hand, lemon and especially lime trees are the most frost-sensitive. If your winter nighttime temperatures are consistently below 35 degrees F, you will need to move the citrus indoors for the winter and provide additional grow lights for the tree. If you only have occasional cold temperatures, covering the tree with frost cloth or using incandescent lights (not LED) to warm the air around the tree are options.
2. Choose a variety suited to containers – Almost any citrus tree can be grown in containers, but many types that are large trees (grapefruit and types of lemons) will outgrow the container quickly. Choose varieties on dwarf rootstock or varieties such as Improved Meyer lemon, Bearss lime, or Kumquat that are naturally smaller trees and they will last longer in containers. Dwarf trees produce the same size and quality of fruit but yield 50-60 percent less fruit. When purchasing your tree, keep in mind that smaller trees are easier to plant and suffer less from transplant shock problems.
3. Use the correct container – Pot should be larger than nursery pot of tree to give the roots room to grow. Use a large (28 inches or larger) durable pot. A half wine barrel is a good choice. Non-porous ceramic pots also work well. If you live in an area that gets cold in the winter, consider how you will move the pot. The pot should have several drain holes spaced evenly around the circumference of the pot, not just one in the middle, to ensure good drainage. Drill additional holes if necessary. It is best to have the pot off ground on pot feet rather than sitting in a tray (standing water can breed mosquitoes).
4. The right soil gives life to your tree – Lightweight potting mix that drains well with inorganic ingredients such as perlite, vermiculite, coconut coir or peat moss added in is best. A soil that is all organic matter will decompose too quickly and become compacted, reducing aeration for roots. Avoid soils that contain chemical-wetting agents — these retain too much moisture. Native soil is also too compacted and will not give roots the air they need.
5. Plant tree at the right depth – Remove plant from nursery pot and plant at original soil level of the nursery pot with graft union (the small bump or scar where the fruit variety was grafted to the rootstock, usually 4″ to 8″ above the root ball) above soil line. Backfill pot, leaving 1-2 inches at top of pot to allow for irrigation. Water pot well and add more soil if settling occurs. Roots should not be visible in dirt. Do not have soil pushed up around the tree trunk.
6. Water correctly – Citrus roots like moist but not soggy conditions. The watering needs of citrus will be different when they are in containers because roots will dry out more quickly. A moisture meter can help you determine when it is time to water. The top of soil may feel dry — test it out by putting meter down deeper by roots. Water thoroughly until water begins to drain out of drain holes. In the hottest times of year, containers dry out very quickly — you may need to water a few times a week. In cooler weather, you will need to water much less. Pay attention to the foliage. Leaves that are wilted and then perk up after watering are a sign of roots that have been allowed to dry out too much. Water more often. Yellowed or curled leaves that do not improve after watering may mean they are getting too much water. Water less often.
7. Citrus trees are heavy feeders and need regular fertilizer – Remember that this tree is dependent on you for nutrients (and water) — its roots can’t go looking for other sources if you do not supply what it needs. The more frequent watering that is required for citrus in containers causes fertilizer to wash through soil more quickly. Slow-release granular citrus fertilizers contain trace minerals like iron, zinc, and manganese, and are good for citrus in containers. The amount you apply will depend on the type of fertilizer as well as the size and age of the tree (follow label instructions for amounts). Fertilize citrus in containers every other month during the growing season. Yellow leaves can be a sign of lack of fertilizer (or over-watering, see above).
8. Take care when pruning your tree – Suckers below graft union should be pruned. Suckers sap energy from the tree and do not produce fruit. Prune dead branches. Citrus can be pruned for size, shape, and balance, but it is not necessary. Prune in the spring, after chance of freeze has passed and before new growth appears. Take care when pruning as exposed bark can be sunburnt. It is best to not prune lower branches. Use water-based latex paint to cover exposed bark.