agapanthus

3 causes of yellow leaves on a lily of the Nile

 

The lily of the Nile is such an easy grower (best in USDA zones 9 through 11) but no plant is completely free of problems.

Full disclosure: I get commissions from purchases made through links in this post. I haven’t received any products for free — all of the ones I refer you to are those that I purchase and use.

One of the Agapanthus’ most common maladies is yellow foliage. There are a number of reasons the strap-like leaves may turn yellow so let’s dive into them and see if we can show off those gorgeous purple flowers against a backdrop of green leaves, not gold.

Full disclosure: I get commissions from purchases made through links in this post. I haven’t received any products for free — all of the ones I refer you to are those that I purchase and use.

Lack of iron

Whenever any plant’s foliage begins to turn yellow you should expect iron chlorosis, especially if the yellowing is occurring on new growth yet the veins remain green. Now it’s easy to assume that that the soil is to blame but it may just be that the soil has sufficient iron but the lily of the Nile has a problem absorbing it.

The first thing you’ll want to do is to test the soil to be sure it’s not the culprit. You can do that with a soil testing kit available at Home Depot or Lowe’s or at your favorite nursery and online at Amazon.com. If the soil pH registers higher than 7, lower it to 6.5 or the plant’s roots can’t absorb the iron in the soil. Use a layer of sulfur spread on top of the soil to lower the pH. It’s always best to follow the label instructions but I’ve found that I’ll typically get a reduction of 1 point in pH with 12 pounds (per 100 feet) of a soil amendment containing sulfur. You’ll need to water right after the application and you may need to reapply again in two months – check the soil again to determine.

If, on the other hand, the pH is within the normal range we’ll need to look at other possibilities. How often do you water the lily of the Nile? Too much water leaches iron from the root zone, so if you think you may be overwatering, try cutting back.

Too much or too hot

Yes, agapanthus produces the best flowers when it’s grown in full sun but when the weather heats up that sun may just be scalding the leaves. Is your lily-of-the-Nile growing with a southwestern or southern exposure? Is it getting enough water? These are two other contributors to sun scald.

Bugs

Agapanthus is a favorite cuisine for both mealybugs and red spider mites. These little critters scrape the foliage to create an opening from which to suck out the juices. As you can imagine, a large enough infestation can wreak havoc on the plant’s leaves, turning them quite yellow.

The best way to get rid of these creeps is with insecticidal soap sprayed on the leaves (both sides). Keep applying the soap weekly until the infestation is gone. Follow the label precautions and apply it on a windless day.

Fungus gnat babies (larvae) munch on the lily-of-the-Nile’s roots, disrupting the flow of moisture throughout the plant and turning the leaves yellow. Since they live in the soil, a soil drench that contains Steinernema feltiae (beneficial nematodes). It’s important to keep these guys alive before using them so if you won’t be drenching the soil immediately, refrigerate them.