By Eddie Ayers, County Extension Agent
Just as we communicate through facial expressions and the spoken and written word, plants communicate as well. It is important for gardeners to understand the language of their plants. This is true for treasured indoor houseplants and plants in the landscape. When leaves start turning yellow that is a plant’s way of telling you that it needs your attention. The top 10 reasons for yellow leaves are under watering and overwatering (which top the list), lighting, temperature, soil condition, nutrients or lack thereof, insect pests, disease, transplant shock, and age.
Whatever the cause, remember that it may take weeks or even months for your plant to recover and return to normal growth. The reality is that if you can’t provide the proper environmental conditions for your particular plant’s needs (water, light, nutrients, and temperature) then it can’t thrive. This week I will discuss four of the reasons for yellow leaves.
Let’s start with overwatering. Overly moist soil is often the result of well-intended, but overzealous, watering. Overwatering leaves the plant’s roots saturated and unable to “breathe” because of the excessive soil moisture. In essence, you’re drowning your plants. If your plant is in a container, make sure it has drainage holes and water less frequently. If there’s a green crusty appearance to the soil surface, this is algae and it too is an additional symptom of overwatering. If the plant isn’t too far gone, you’ll probably want to repot it into new soil. Check the roots: white roots are an indicator of healthy plants; black roots that appear to be decomposing are a death knell. When repotting an overwatered plant with rotting roots, trim back those roots that are in decline leaving the healthy roots to recover.
If you feel that the cause is not enough water, the remedy is obvious. Make sure you’re watering your plants properly: wait until soil begins to dry, then drench it fully, and wait until the soil begins to dry out before watering again.
Temperature and light of course play a significant role in plant health. If your leaves appear more faded than truly yellow, this could be a sign of lack of sunlight. Plants need proper light for photosynthesis to occur, the lifeblood of any plant. For plants in containers, be sure to rotate the pots periodically so that all the foliage is exposed to sunlight.
Research the light needs of your specific plant and make sure you’re providing the right type of light. Some plants like bright, but indirect, light. Others prefer full sun, yet others thrive in low light. If your plant is getting too much or too little light it will let you know. Plants with too little light also tend to become “leggy” as they’re reaching for more light with stems becoming atypically long with the leaves growing undersized. Sometimes the leaves may even fall off.
Though seen more often in landscape plants than houseplants, a significant temperature change can leave leaf tips looking “burned.” This typically occurs in spring, when there is a late freeze after tender new growth has emerged. If this is the case, trim off the “burned” foliage and allow new growth to re-emerge.
Houseplants have preferred temperature ranges. Some like it cool, around 50-60 F, others prefer 70s and 80s. Some prefer high humidity, others not so much. Some plants will drop all their leaves as a stress response to change when moved from one location to another, only to subsequently rebound with new growth. Ficus are particularly known for this.
Tune in again next week for the remaining reasons that plant leaves turn yellow. Susan Jasan, horticulturist and landscape architect, and State-By-State Gardening contributed to these articles.