What to Do When Your Plants Are Yellow
Yellowing plants can be common in the heat of summer and are caused by several factors: chlorosis, fungus, and watering issues. Below are to use in order to diagnose what’s causing your plants to yellow and learn how to treat them.
Yellowing from Chlorosis
At this time of year, it’s not uncommon to see a slight to severe yellowing of the leaves of certain plants and trees like Bradford pears, citrus, hibiscus, grape vines, roses, etc. While leaf yellowing can be an indicator for over watering or poor drainage, it is also an indicator of chlorosis, which simply means yellowing of the leaf due to a lack of chlorophyll. Causes of chlorosis include poor drainage, high alkalinity, and nutrient deficiencies in the plant.
Nutrient deficiencies occur because there is an insufficient amount in the soil or because the nutrients are unavailable due to a high pH (alkaline soil). The lack of iron is one of the more common nutrients associated with chlorosis. Manganese or zinc deficiencies in the plant will also cause chlorosis. The way to separate an iron deficiency from zinc or manganese deficiency is to check what foliage turned chlorotic first. Iron chlorosis starts on the younger or terminal leaves and later works inward to the older leaves. However, manganese and zinc deficiencies develop on the inner or the older leaves first and then progress outward. Plants need iron for the formation of chlorophyll. Chlorophyll gives leaves their green color and is necessary for the plant to produce the food it needs for its own growth. Iron is also necessary for many enzyme functions that manage plant metabolism and respiration. Iron becomes more insoluble as the soil pH climbs above 6.5 to 6.7 (7.0 is neutral – below 7.0, the pH is acidic; above 7.0, the pH is alkaline). With most plants, iron can only be absorbed as a free ion (Fe++) when the pH is between 5.0 and 6.5.
The treatment we recommend for poor drainage, iron deficiency and high pH is 1st Step Soil Acidifier, the new formulation has iron and zinc, in addition to sulfur.
Yellowing From Watering Issues
Diagnose whether you’re overwatering or if your soil isn’t properly draining. Yellowing leaves are the typical sign of over watering. Crispy, brown-edged leaves are a sign of high alkalinity and salinity. Salt causes the edges of leaves to burn. The build up of salt in the soil can also cause standing water, which is an indicator that your soil isn’t properly draining. Counteract these problems by treating the soil with an acidifier. Using this product will leach salt out of the plants’ root zone, loosen the soil in general, and release nutrients that are bound up by the high alkalinity. To get back on track, water plants deeply. Running a drip system three times per week for 1.5 hours will keep the soil in the root zone moist enough for most plants.
NOTE: Even in high heat, don’t change your watering schedule to every day. Rather, keep a 2 or 3-day per week schedule and water more deeply. See the adjacent chart. The best way to determine if your plants are getting enough water is to inspect them daily for wilt and dry soil. If the soil dries out (not at the surface but deep by the roots) before the next scheduled watering and the plant is wilted, it needs more water. Give it some interim water and adjust your time clock. If you have questions, contact your local nursery.
|Duration & Frequency of Watering||Veggies & Flowers T-Tape||Vines & Shrubs1 GPH||Shrubs & Trees4′-5′
|Shrubs & Trees5′-10′
|Potted Plants on Drip||LawnsSprinkler|
|Time(Hours)||2-3||2||2||2||4||30 min||10-20 min.|
|Days per Week||2||2||2||2||2||3||3|
Leaf wilt can also be a result of hot winds. If you’re watering seems to be on track, i.e. no standing water, good deep soaks that mostly dry out between waterings, and you’re still experiencing leaf wilt or even some drop off, then the culprit is likely our summer winds. Generally, plants will come back from this in time, but may look a little pitiful in the meantime. When summer is past, trim the plant lightly, fertilize and you’ll see them bounce back.
Queen palms and lawns are the first to show symptoms of common summertime gardening challenges. If your palm has yellowish fronds and new fronds are emerging with accordion-like folds, your palm may be suffering from nutrient deficiencies or heart rot, both of which are common in the summer. Queen palms are tropical palms that love acidic soil and must have iron and manganese to stay healthy and green. If you haven’t acidified your soil and fertilized with a micronutrient mix containing iron and manganese, and your palms are looking yellowish and spindly, apply a soil acidifier and fertilize with a micronutrient mix and a Palm food. If your queen palm doesn’t show significant improvement within three weeks after acidifying and fertilizing, heart rot may be the cause of your palm’s maladies. Heart rot is a fungus transmitted from tree to tree on birds’ feet. This fungus is very prevalent in the Valley and easily treated by applying to the center of the palm a mix of water and a copper sulfate powder which should be available at your local nursery.
Kari Petterson is with Gardener’s World
located at 3401 E. Baseline Road in the South
Mountain District. Contact Gardener’s World at