Preparing for the arctic deep freeze this week reminded me that many of us have seasonal or tropical plants that we bring indoors at the end of the season to overwinter. This practice allows us to have some living color during the bleak, gray days of winter and perhaps even a little fragrance or bloom.
The most common plants brought indoors belong to the citrus family (lemons, limes, grapefruit, kumquats, tangerines). However, transitioning citrus plants to indoor life can present some challenges. I recently visited a struggling lemon tree and was inspired to share a few best practices to keep your citrus plants happy during their indoor winter “plant-cation.”
Select a variety that is well adapted to growing in a container and indoors. According to the University of Minnesota Extension fact sheet “Growing Citrus Indoors,” the following species perform well as indoor houseplants with proper care and management:
• Calamondin orange (Citrofortunella mitis).
• Citrus limonia or Otaheite orange-lemon/tangerine cross.
• Tangerines (Citrus reticulate). Satsuma oranges, which are really tangerines, are exceptionally good and produce a fragrant bloom.
• Lemons, such as the Ponderosa or Meyer varieties.
• Citron (Citrus medica) and kumquat (Fortunellla species).
Treat your citrus plant as a large houseplant. Upon transfer indoors, monitor your plant for common pests (scales, whiteflies, spider mites, aphids). Keep leaves clean by periodically washing the foliage, and acclimate your plant appropriately.
Select a suitable growing medium. Citrus plants prefer a slightly acidic, well-drained medium. A good choice is a cactus mix or commercial medium with up to 1/3 inorganic material (small pea gravel, pumice, turkey grit, etc.) for improved drainage. Do not use a mixture designed for moisture retention.
Since citrus plants prefer a well-drained growing environment, select a container with sufficient drainage. Select your container based on the size of your plant; start with smaller pots for smaller plants and repot as the plant grows. A deep pot is better than a shallow one. This helps to balance the plant as it grows larger and top-heavy. It is suggested that plants be repotted every one or two years.
Watering your container citrus can be tricky. Citrus plants prefer regular watering so that the soil is moist, never soggy or wet, and slightly dry between waterings. The amount and frequency depends the size of your container, size of the plant, humidity, temperature and growing medium. Plan to reduce watering during the plant's nonactive growth periods, i.e. during the winter months. Common symptoms of too much water are cupped or yellow leaves.
Manage sun exposure and winter light. Citrus plants do best when the plant receives as much bright light as possible. Make sure to place your plant in a south or southwest indoor area to maximize sunlight exposure. Citrus trees do not enter dormancy like other plants, but do slow their growth habits during the low-light months of winter. Supplemental lighting and some humidity is necessary, especially if you are aiming to produce fruit.
Follow preferred temperatures and acclimation periods. The best temperatures for citrus plants are between 55 and 85 degrees Fahrenheit. Sudden, drastic shifts in temperature are not tolerated well. A 5- to 10-degree difference in day and nighttime temperatures is required for flowering.
Citrus plants can return outside once temperatures consistently remain above 50 degrees. Keep in mind that a one- to two-week transition period is needed when moving indoor plants outdoors or outdoors plants inside. Acclimation should include a gradual move of the plant from a sheltered, partly shaded area into full sun. Not acclimating the plant properly may cause sunburned leaves, and/or leaf, flower or fruit drop.
Once acclimated, consider relocating the plant to a sunny location with protection from the wind where it will receive a desirable amount of water. Avoid areas where water accumulates or near watering or lawn sprinkler systems. Additionally, consider a landscape microclimate, such as near a building where heat is reflected from a patio or walkway, for seasonal outdoor placement. Move citrus plants indoors before night temperatures reach 40 degrees.
Feed your plant properly. Citrus plants require large amounts of nutrients, and need higher amounts of nitrogen over phosphorus or potassium. Specialized fertilizers are available for citrus, but a good all-purpose or acid-loving plant fertilizer can be used.
Be sure to choose a fertilizer with at least a 2-1-1 NPK ratio. Granular, slow release formulations are best, but frequent dilute applications of soluble fertilizer can be made when the plant is actively growing (April-September). Be sure to follow all label instructions.
Heather Neikirk is a Stark County Extension educator in agriculture and natural resources for the Ohio State University Extension. Contact her at 330-832-9856 or firstname.lastname@example.org.