Citrus Care Guide

Growing citrus trees, whether in containers or directly in the ground, can be a rewarding experience. With the right care and attention, they can thrive and produce beautiful, fragrant fruit. Here's a comprehensive guide to help you cultivate healthy, productive citrus trees.

Citrus varieties are generally hardy in zones 8-11, but will need to be container grown and brought inside during Winter months in colder climates. 

Planting Citrus in a Container

Container Size & Type:
For long-term growth, a 15-25 gallon container is ideal for most citrus trees. This provides sufficient room for the roots to expand over the years. It is important to graduate pot sizes incrementally, as a small root system in a larger pot will likely sit too wet and rot. If the tree becomes root-bound, you can prune 1/3 of the roots and trim the top by 1/3 to encourage a bushier, dwarf form. Do this before the new spring growth begins.

Soil Mix:
Citrus trees prefer light, well-drained soil. A packaged mix like Foxfarm ‘Strawberry Fields’ works well. You can amend it with compost, rock phosphate, and lime to add nutrients. Avoid boggy soil, as it will suffocate the roots. A slightly sandy, well-draining mix with some bark chips can also work well. Ensure that the graft union (the area where the scion is grafted to the rootstock) is above the soil line to avoid potential issues. The very top of the root flare should also be exposed above the soil line to prevent root rot. 

Temperature & Lighting:
Citrus trees thrive in warm conditions, so try to maintain a nighttime soil temperature of about 70°F indoors. If that's difficult, use a horticultural heating mat. For optimal growth, ensure the tree gets plenty of sunlight—near a south-facing window is ideal. If growing indoors, fluorescent or full-spectrum lights can help supplement natural light, especially in Winter months. Keep lamps lit for 16 hours during these periods. 

Watering

Frequency:
Water when needed, making sure the soil stays moist but not soggy. Good drainage is crucial—water should drain easily from the pot. Avoid letting the tree dry out, but also avoid over-watering. In the ground, maintain a deep basin around the tree for watering.

Watering in Containers:
Ensure there's about 1 inch of space from the soil surface to the top of the container for watering. It's important to maintain moisture levels in the soil and provide good aeration to the roots. In Winter, let the top inch of soil dry before adding more water. 

Watering in the Ground:
In well-drained soil, water established citrus trees once a week during dry periods. In heavier clay soils, water more deeply every 2–3 weeks, allowing the soil to dry out slightly between waterings.

Fertilizing

Fertilizer Type:
Citrus trees need plenty of nitrogen during their growing period. Use a balanced, all-purpose fertilizer or a dedicated citrus fertilizer such as Citrus Tone. Fish emulsion or other organic fertilizers work well too. Avoid fertilizing while the plant is dormant during the winter months. Citrus respond well to frequent foliar feeding in addition to the slow release fertilizer. Southern Ag Citrus Nutritional Spray or something similar can be used during the growing season and sprayed on the foliage according to the package instructions. 

Signs of Nutrient Deficiency:

• Yellowing leaves often indicate a lack of nutrients or poor drainage.
• Magnesium deficiency is common in potted citrus, which can be corrected by adding Epsom salt (1 tsp per 3 gallons of soil).
• Citrus trees may also benefit from minor nutrients like zinc, iron, and manganese, which can be applied as chelates or micronutrient mixes.

Fertilizing Schedule:
Fertilize only during active growth, which typically happens in spring and summer. Avoid fertilizing during the winter when the tree is dormant.

Pruning & Suckering

Pruning:
Citrus trees require minimal pruning. However, if the tree develops erratic or overly long branches, trim them back. Citrus trees will naturally round out over time, and you can pinch off the tips of new growth to encourage bushier growth.

Suckering:
If your citrus tree has a grafted rootstock, be sure to remove any suckers (growth below the graft) as they are often thorny and less productive. These suckers can draw energy away from the main tree and should be cut back promptly.

Pest Control

Citrus trees can attract a variety of pests, including aphids, mites, scale, and whiteflies. These pests can distort leaves and affect overall health and fruiting. If you’re growing your tree in a container and bringing it inside during Winter, pay extra attention to pest issues as they are typically more prevalent indoors. 

• Aphids: Use rubbing alcohol (65%) diluted with water to control aphids. Spray it on both sides of the leaves. Repeat every 5 days if eggs are present.
• Mites: Consider using Azatin (Neem oil extract) or Botaniguard as both an insecticide and fungicide.
• Scale: use rubbing alcohol to wipe active scale off of leaves and branches. Scale tends to collect by the leaf stem, underneath leaves, and where branching begins. If you notice ants crawling on your tree you probably have scale. Wipe them off with alcohol and repeat at least twice in 5 day increments even if you don’t see new scale present. This ensures the eggs will also be controlled. 
• General Pest Control: Use Murphy’s Oil Soap to smother pests like mites and aphids. It can also help shine the leaves.
• Horticultural Oils: A mixture of horticultural oil, Botaniguard, and silicone (Silmatric) can help control a range of pests.

Growing Citrus Indoors & Under Glass

• Light: Citrus trees need bright sunlight to thrive. If you're growing them indoors, ensure they receive as much light as possible, and rotate them regularly to ensure even growth.
• Humidity: In dry indoor environments, consider mist spraying the leaves, or place a plastic bag over the tree at night to maintain humidity.
• Temperature: Protect citrus trees from drafts or sudden temperature fluctuations, especially during the winter months.
• Hardening Off: If moving trees from indoors to outdoors, transition them gradually by placing them in semi-shade first to acclimate to the outdoor conditions.

Winter Care

In colder climates, citrus trees should be brought indoors before temperatures drop significantly. Hardier varieties like Satsuma or Meyer lemon can tolerate light frost but should still be sheltered from freezing temperatures.

• Location: Place the tree in a warm, sunny spot. Near a south-facing window is ideal (be mindful of placing the plant too close to the window pane especially if it’s an older, drafty window that gets cold at night). 
• Humidity: Low indoor humidity during winter can cause leaf drop. Use a humidifier or mist the leaves occasionally to maintain humidity.
• Winter Dormancy: Citrus trees tend to slow down during the winter months. Avoid fertilizing during this time, and wait until spring growth resumes before repotting or pruning.

Rootstock Information:

Carrizo Rootstock is a hybrid of Washington Navel orange and Poncirus trifoliata (trifoliate orange). It’s often used for its cold tolerance and nematode resistance.

• Fruit Quality: Trees on Carrizo rootstock tend to produce medium-sized fruit with a smooth rind and high juice content.
• Compatibility: Carrizo is compatible with most varieties of navel and Valencia oranges but incompatible with Eureka lemons (which may develop a yellow ring at the bud union).
• Tolerances: This rootstock is resistant to phytophthora, nematodes, and Tristeza, but it doesn't like high pH soils, clay soils, or waterlogging.
• Maturity: Fruit maturity is earlier than other rootstocks, making it a good option for certain climates.

Macrophylla or Tahitian Lime rootstock is good for indoor citrus because it doesn’t go dormant like trifoliate and many varieties benefit from the non-dormant nature of this rootstock.

Flying Dragon Trifoliate (also sold itself as a cold-hardy citrus) is a good dwarfing rootstock for citrus. 

By following these guidelines, you can successfully grow citrus trees both indoors and outdoors. They require some attention, but the rewards—fragrant blooms, lush green foliage, and sweet, homegrown fruit—make it all worth it!