Citrus trees (Rutaceae)
While citrus trees are commonly associated with hot climates, they can also thrive in milder temperatures or be grown in pots, producing a significant amount of fruit. Among the many varieties available, the most familiar are basic lemon, mandarin, and orange. When purchasing a citrus tree, choosing a variety that produces fruit you enjoy is essential, as there are notable differences in taste, size, and growing requirements.
For instance, I have a mandarin tree that yields small, sweet fruits. However, other varieties, often grown in my region, produce large, dry, and quite bitter fruits. These types are well-suited to colder climates, so if you ask for a variety that can survive cold winters and be planted outdoors, you might end up with one. This is why careful selection is essential to ensure the tree meets your expectations.
Lemon Trees
Lemon trees are more cold-sensitive than mandarins, so these are more suited for warmer climates or indoor growth. They can tolerate short periods of frost if protected. Varieties like Meyer lemons are more cold-tolerant than others.
I grow lemon trees in pots, which allows me to keep them in the greenhouse during autumn and winter. I then put them outside when the temperatures rise. Like this they stay in ideal ambient and I don’t have to pollinate them manually (wind and rain does its work).
Growing requirements
A lemon tree needs a direct sunspot with at least 6 – 8 hours of daily sunlight and well-draining, slightly acidic soil with a pH between 5.5 and 6.5.
Grow as smaller trees (4–6 meters / 13–20 feet) and are ideal for pots or small gardens.
Watering
Young Trees: Keep the soil consistently moist but not soggy.
Established Trees: Water deeply but allow the soil to dry slightly between waterings.
Potted Trees: Water more frequently, as pots dry out faster.
Fertilizing
Use a citrus-specific fertilizer rich in nitrogen. Feed the tree every 4–6 weeks during the growing season (spring and summer). Avoid over-fertilizing in autumn and winter to prevent weak growth.
Mandarin Trees
Mandarin trees are usually more suitable for colder climates; they can withstand mild frost for short periods when planted outdoors. Anyway, we can easily grow them in pots.
Growing requirements
Thrive best with prolonged, direct sunlight for sweeter fruit. Prefer soil pH closer to 6.0 to 7.0 for optimal growth.
Slightly smaller trees (2–4 meters / 6–13 feet) and often bushier, making them suitable for smaller spaces or pots.
Watering
More drought-tolerant than lemons and oranges, needing less frequent watering once established.
Fertilizing
Need slightly less fertilizer than lemons, as their growth is slower and less nutrient-demanding.
Orange Trees
They prefer consistent warm climates and are slightly less tolerant of cold than Mandarins. They can survive light frost but require protection in colder regions.
Growing requirements
Thrive best with prolonged, direct sunlight for sweeter fruit. Prefer soil pH closer to 6.0 to 7.0 for optimal growth.
Grow larger (6–10 meters / 20–33 feet) and require more space, though dwarf varieties are available for smaller gardens or containers.
Watering
Require moderate, consistent watering—neither too much nor too little.
Fertilizing
Similar feeding needs apply to mandarins, focusing on balanced citrus fertilizers with periodic supplements of potassium and phosphorus.
Standard care requirements for citrus trees
Lemons usually produce fruits year-round; mandarines and oranges vary from a single harvest season (usually during autumn and winter) to two seasons (usually dwarf varieties).
Usually, the plants should not be fertilized during the cold dormant season because they would be stimulated to grow and produce fruit, even if they should have time to conserve their energy for the growing season.
Pruning
Prune in late winter or early spring to remove dead or damaged branches. Trim to shape the tree and allow sunlight to reach all parts. Remove suckers (shoots growing from below the graft) to focus energy on fruit production.
If the branches and leaves are overgrown, it creates excess shadow to flowers and developing fruits and creates a perfect humid environment for diseases and pests.
Pests and diseases
Citrus trees grown in pots are very susceptible to pests. Control your plants regularly to avoid severe damage.
Common pests include aphids, scale insects, and spider mites. Use insecticidal soap or neem oil as needed.
Prevent root rot by avoiding overwatering and ensuring proper drainage.
Watch for yellow leaves, which may indicate nutrient deficiencies or overwatering.
For example, scale insects are prevalent, highly reproducing pests that feed on plant sap. When plants have these pests, you will see sap coming out of the plant (like if the trunk would be wet). Then, you will see these small white insects hiding in damp and hidden areas (between branches and down the leaves). Remove all of them using the correct procedure and repeat it until there is not even one (eggs can often remain after one procedure). Also, proper pruning is highly recommended.
Pollination
Many citrus trees, such as oranges, lemons, and mandarins, are self-pollinating (or self-fertile), meaning they can set fruit without requiring pollen from another tree.
Pollen from the male parts (stamens) of the flower can fertilize the female parts (stigma) of the same flower or another flower on the same tree – naturally happend with the help of wind and rain.
Cross-Pollination
Some varieties, especially hybrids (e.g., tangelos and certain mandarins), benefit from or require cross-pollination to produce higher yields or better fruit quality.
Cross-pollination occurs when pollen is transferred between flowers of different trees, usually of the same or compatible species.
For varieties requiring cross-pollination, having compatible trees nearby (within 15–30 meters or 50–100 feet) increases the likelihood of adequate pollination.
External factors for pollination:
- Bees: The primary pollinators for citrus trees are bees that are attracted to the fragrant flowers and collect nectar while transferring pollen from one flower to another.
- Other Insects: Butterflies, beetles, and other insects can also contribute to pollination, though they are less common.
- Wind: While not a significant factor for citrus cross-pollination, the wind can sometimes transfer light pollen.
Factors influencing pollination
Flower Timing
Citrus trees produce many flowers in spring, ensuring a high chance of successful pollination.
Not all flowers will develop into fruit, as trees naturally shed some to focus energy on a manageable crop.
Environmental Conditions
Temperature: Pollination is most successful when temperatures range between 18–26°C (65–80°F). Extreme heat or cold can affect flower development and pollination.
Rain: Excessive rain during flowering can wash away pollen and hinder pollinator activity.
Wind: Strong winds can damage flowers or reduce pollinator visits.
Human-assisted pollination
In cases where natural pollination is insufficient, especially for indoor or greenhouse citrus trees, hand pollination can help:
Hand pollination in 3 steps
- Use a small brush, cotton swab, or finger to collect pollen from one flower’s stamens gently.
- Transfer the pollen to the same or another flower’s stigma (the central sticky part).
- Repeat the process across multiple flowers to ensure a higher fruit set.