Care of Citrus- The Basics
LIGHT: Full sun, a southern exposure.
TEMPERATURE: Maintain indoor temperatures above 40. During the winter; however, temperatures above 60 are preferred in order for the plant to absorb nutrients and maintain active growth. Exception: The Citrus aurantifolia “Key Lime” is a tropical citrus and requires that indoor temperatures be maintained above 60. It will not tolerate temperatures below that very well.
HUMIDITY: While citrus enjoy 50% or higher, they will tolerate low levels with no harm. Spraying distilled water on plant occasionally will remove any dust and help leaves function better
WATERING: Bring the soil to a state of visual dryness between waterings. Be careful since some mixes are a dark color and look “wet” when they really aren't. It’s best to grow in a clay pot, which will help with increasing air exchange to the root system. When re-potting, don’t over-pot. Keeping them a little under potted creates a healthier environment for the root system.
FERTILIZER: Frequency of fertilization is important. Every 3 weeks in summer and every 6-8 weeks in winter. Use a balanced fertilizer like a 10-10-10 or 7-9-5. Excessive fertilization can create difficulties in culture, so it’s better to dilute and use more often.
PRUNING: Prune young plants to encourage branching. This will help create a bushy plant and stronger limbs to hold the heavy fruit. The best time to prune is late spring after flowering and when in active growth.
INSECTS and DISEASE: For the most part, citrus is not highly susceptible to insects. However, they will attract scale, mealy bugs and mites if infected plants are nearby. Citrus plants in general are more susceptible to root disease, but following the water recommendations and keeping temperatures no lower than 60 will help negate the problem.
Citrus Care - More Detail
LIGHT: Citrus love light and heat. When keeping indoors a south facing window providing 6-8 hours or more of light is best. The next best is a southwest or west window. Be sure to rotate the plant every few weeks so it doesn't grow too heavy on the light side and to balance all leaves getting their share. LED supplement light fixtures are inexpensive on eBay and Amazon and can provide supplemental light for winter months.
HUMIDITY: Is not a major concern for citrus, although the higher humidity will impart a greater sheen or gloss to the leaves. We recommend distilled water to spray plant leaves with because hard water will leave calcium deposits and spots on the leaves. This can cut back the amount of light reaching the chloroplasts that are primary to photosynthesis. Plants can be sprayed as often as daily with no harm.
WATERING: 90% of the problems with potted plants can be traced back to root issues and root health. Correct watering is a major component of that. Citrus like to be moist, not wet and like good aeration to the roots. Terra cotta pots can be good as they draw moisture away from all levels in the container, however they need to be monitored more closely. Glazed or plastic post are ok as long as the dark color ones do not over heat in our sun when outdoors, burning the roots. 100 degrees on the side of a black pot can be 130-140f on the inside inch of soil. This is where 80% of a container plant's roots are located. Using a tray under your container to catch water overflow is a necessity indoors, but be sure not to let your tree sit in water drowning the roots and keeping soil wet. Using a layer of marbles or 3/4” gravel in the tray will help provide humidity but keep the bottom of the container out of sitting water. After a few waterings you will learn the right amount to give your tree. There is some debate whether there is enough chlorine in tap water to be harmful to plants. Chlorine will evaporate out of an open container overnight and some people plan ahead and use this water for their plants. Water that has been run through a water softener should be avoided as many softeners substitute sodium for the calcium present in hard water. In any case once a month you should “flush” your plant to remove any accumulated and excess salts or fertilizers. Take it outside or put in sink or bathtub and run water through it for a minute or so. In small containers up to 5g let the top 1” of soil dry some before watering, 5 g and over the top 2 “.
POTTING or SOILLESS MIX – Citrus like a well draining, highly aerated mixture. The standard potting soils have too much peat in them and will stay waterlogged at the bottom of the container. Surprisingly, while we usually do not like Miracle Gro products, they do make a good Cactus, Palm and Citrus potting mix, with a 3 month time released fertilizer. Lowes has a STA GREEN Tree and Shrub soil (not potting mix) that is ok if you add about 15% perlite. Many hobbyists use what is known as a 5-1-1 mix which is 5 parts screened Pine Bark under 1/2”,1 part perlite and 1 part compost. This is a little hard to source in small quantities and you will need to screen the bark your self. You must use bark, not interior wood and Pine or Fir not others types like cedar or juniper. Some will add a little sand and azomite to this mix along with a touch of lime since it will be acidic. The acidity is not an issue since we are watering with a high ph water most likely and citrus like a ph 6-7 range.
FERTILIZER- Citrus are heavy feeders and containers by their nature flush fertilizers through with watering, right out the bottom of the pot. For this reason we do not use a lot of organic or fish fertilizers since they take time to break down and become available. Ask 100 growers what to use and you will likely get at least 50 different answers. We feel the best program is to use Osmocote plus which gives long term coverage, in case you forget or are a little lazy on fertilizing. We then use Dyna Gro's Foliage Pro on a weekly basis. It's primary N source is nitrate which plants assimilate directly. Urea is a cheap form of N and needs to be broken down or decomposed before it becomes available, and not recommended as a source of Nitrogen. Foliage Pro also contains all the proper micronutrients in the correct amounts. Grow More Soluble Citrus food seems to be another good one and there are others, you just need to read labels carefully.
PRUNING: Can be done any time of year and is usually to promote branching or retain balance in a tree. A heading cut will result in the nodes below the cut becoming branches. Do not use any for of tree sealer on pruning cuts, they will heal fine, sealers can lock in bacteria and fungus causing problems down the road. Broken, dead or crossing branches should be removed for best production.
TEMPERATURE: Citrus love heat, the more the better. In spring after all danger of frost is past, move your plant outside. Slowly harden off since it is not yet used to full sun. After that they can be kept in full sun or shaded from afternoon sun a little if you prefer. Make sure to monitor water needs because full sun will dry container plants quickly. Citrus do best when grown above 50f, their preferred range being 70-90f. In winter indoors, a warm room with southern window will give best growth. Their main growth period is March – October when days are longer. If you have it in a real cold room over winter you can get a waterproof heat mat to put under it. These are inexpensive, often used for seed starting and sell on eBay and Amazon for less than $15.
REPOTTING – If you received a tree grown in a 1 qt container, you should move it up to a larger size right away. We usually sell these when the container is full of roots and ready to repot. You should move your tree up in steps as it grows. The 1 qt size you receive should move up to a 1 or 2 gallon container. Moving to a bigger container will result in the soil stayng too wet for a prolonged period. When the bigger roots are growing out of the bottom, you know it is time to move up to a larger size. At this point when repotting, check the roots. Any dark or black roots should be cut out and show plant is too wet. Roots should be spread out when you move up to a new container. Any circling or bad roots can be cut off and just like pruning, where you cut the root it will cause it to branch multiple new roots. This helps develop a good fibrous root system that will spread in the container. It is best to not remove more than 24% of roots at 1 time and if you do, the top of tree should be pruned to compensate and balance.
We have covered and provided and covered a lot here and there is much more info on the internet about growing citrus in containers as well as Facebook groups dedicated to it. Citrus are actually very easy to grow and rewarding by just following some basics.