If you’ve ever grown geraniums, odds are pretty good you’ve asked yourself, “Why on earth are my geranium leaves turning yellow?!” It happens to the best of us, but it is manageable and, yes, even preventable. There are several reasons why geranium leaves may begin to turn yellow and drop off. Common causes include geranium diseases, light exposure, and nutrient deficiencies. We’ll take you through them one by one to make sure your geranium plants remain lush and beautiful.

Why grow annual geraniums

Annual geraniums offer big, blowsy colorful blooms, interesting foliage, and, in the case of scented geraniums, eye-opening fragrances like chocolate mint, rose, and citronella, among others. Some different annual geraniums to try include “Chocolate Cherry” zonal geranium, “Crocodile” ivy leaf geranium, and “Grey Lady Plymouth” scented geranium.

Now, it’s worth noting that “geranium” can refer to hardy geraniums which can be planted in outdoor beds and treated as perennial plants. But there are other “geraniums” which are actually a kind of tender annual geranium relative from the Pelargonium genus. Unlike hardy geraniums, in most climates Pelargoniums must overwinter in a protected greenhouse or be grown indoors as houseplants.

What to do about geranium leaves turning yellow

If you notice geranium leaves turning yellow and your plant is growing in a pot that can easily be repositioned, start by taking stock of your plant’s access to light. These sun-loving plants need about six hours of direct sunlight per day. Without adequate light, geraniums have difficulty completing photosynthesis, resulting in spindly, yellowing growth. Fix any lighting issues you may have, and the plant’s green color should improve.

6 causes for geranium leaves turning yellow

The most common reasons for geranium leaves turning yellow include infections, lack of nutrients, pest infestation, too much water, too little water, and physical damage from, say, exposure to frost or even herbicides. In conjunction with yellow leaves, you might notice other troubling symptoms such as wilting, brown spots, and dropped leaves. Here are six of the most common reasons for geranium leaves to turn yellow:

Cause & Fix 1: Geranium diseases

Geranium leaves may look yellow and stunted when attacked by bacterial blight, Botrytis blight, and Verticillium wilt. (Botrytis—sometimes called “gray mold”—is a fungal infection. So is Verticillium wilt.) 

When it comes to these highly infectious diseases, it’s game over for your plants. Remove and discard them and instead focus on prevention, moving forward. When watering, avoid splashing plant leaves, since this is a common cause of pathogen spread. Also, space plants so that light and air can circulate around them.

Cause & Fix 2: Nutrient deficiency

Unsure about the nutrients and pH levels in your soil? Soil testing may be advisable—particularly for new planting beds. Send samples to your area extension agency to see if you have specific nutrient deficiencies that need to be corrected. If you notice the lower leaves on your geranium plants starting to yellow, they may have a nitrogen deficiency. This sometimes causes plants to cannibalize missing nutrients from their own older leaves. A magnesium deficiency, similarly, affects older leaves first. Look for yellowed areas beginning near leaf veins.

Although annual geraniums aren’t heavy feeders, supplemental fertilization has its place. To keep plants healthy, water in an all-natural balanced fertilizer a couple of times each season.

Cause & Fix 3: Geranium pests

Another reason you see geranium leaves turning yellow? Common pests like aphids and spider mites sometimes target annual geraniums. Besides the aphids and (tiny!) spider mites themselves, look for evidence of the sticky honeydew and fine webbing that each respective pest leaves behind. Pick off small infestations by hand or control with an insecticidal soap or peppermint spray.

Cause & Fix 4: Overwatering geraniums

Overwatering just might be the most common reason for geranium leaves turning yellow. Annual geraniums dislike wet feet and prolonged exposure to standing water can contribute to root rot. In other words, all the extra moisture in the soil smothers and subsequently rots plant roots. In time, the affected plant’s leaves turn yellow, die, and drop off.

Allow waterlogged plants to dry out and, before watering, check the top few inches of soil to determine whether water is needed. Use your finger to gauge moisture levels.

Cause & Fix 5: Underwatering geraniums is a common reason for geranium leaves turning yellow

While excess water is a problem, you don’t want to under-water your annual geraniums either. Many hardy (perennial-type) geraniums are relatively drought-tolerant; however, annual geraniums are often less so. Make sure they get at least an inch of water per week during hot weather.

Also, any annual geraniums you’re growing in containers need to be watered a little more frequently, since they dry out more quickly than their in-ground counterparts. Finally, when watering, try to keep the foliage dry and instead direct water straight to the root zone. I use a long handled watering wand to direct water to the growing mix.

Cause & Fix 6: Weather or herbicide damage

If you live in a climate with periodic frosts and you put your annual geraniums out in very early spring or late fall without thinking about your first and last average frost dates, you run the risk of exposing your plants to frost damage. This causes plant leaves to turn yellow and die back. Have an unexpected freeze in the forecast? Protect plants that are already in outdoor garden beds or pots by temporarily covering them with frost cloth or floating row cover.

The chemical drift from herbicides is a risk to human, pet, and plant health. If you see that your geranium leaves have begun to yellow—and you’ve checked into all of the other possible variables—you might be seeing the result of unintentional herbicide damage. If you suspect this is the case (perhaps from a neighbor?), water the plant well to try to dilute the concentration it’s able to take in through its roots.

How to stop more geranium leaves turning yellow

First, trim off any yellowed leaves you see. (This will make keeping tabs on any new or emerging problems easier.) Next, retrace your steps to identify what went wrong. Was it too much or not enough water? Do you see signs of fungal or bacterial disease or insect activity? Once you’ve mitigated the problem and your plant is looking good, make sure to provide ideal growing conditions.

Proper growing conditions for geraniums

Providing ideal growing conditions can help to prevent the all-too-common problem of geranium leaves turning yellow. If you plan to grow your annual geraniums in outdoor garden beds, make sure your soil drains well. Amend the soil with sand and organic matter like finished compost in order to improve its overall fertility and structure. If you’ll be growing your plants in pots, use only those with drainage holes and choose a lightweight, nutrient-rich potting soil. (Potting mixes containing perlite help to improve both drainage and root zone aeration.) As for light, aim for six hours per day—morning sun with some afternoon shade is best.

More tips for geranium success

• Boosting blooms—Remove spent flowers to encourage additional, new blooms.
• Encouraging bushier growth—If plant growth looks leggy, make sure it’s getting enough light. Also, pinch or clip back the leggy sections to encourage bushier, more compact growth. 
• Adding winter light—For plants overwintering indoors, consider using supplemental grow lighting as needed.

The fix is in for geranium leaves turning yellow

If you see your geranium leaves turning yellow, now you know there are several potential causes, including overwatering, under-watering, insect infestation, certain pathogens, and nutrient deficiencies. Your plants can also suffer damage from exposure to cold snaps and herbicides. Fortunately, now you also know how to fix these issues and, better still, how to prevent the problem of geranium leaves turning yellow in the first place.

Remember, for consistently healthy foliage, your annual geraniums need plenty of sunlight, a regular watering schedule, and well-draining soil. Good air circulation and routine disease and insect pest checks are a big help, too.

For more articles on growing annual plants, be sure to check out these articles:

• Dichondra Silver Falls: A grow guide
• The easiest flowers to grow from seed
• When and how to plant sweet peas
• How to grow calendula