Agave leaves turning yellow

Agave plants are best known as succulent plants with large leaves that end in spiny tips. At first glance, you probably wouldn’t call agave plants rosettes, although they are. So many of the common ones are spiny succulents, with leaves that jut out in often dangerous spikes. There is a lot of variety in the agave genus. There are the large, stiff specimens that can grow to 20 feet in diameter. There are also small dish-sized agaves, and agave plants with soft leaves and no spines, although most do have leaves that end in a sharp point.

  • Leaves: Agaves are all stemless, or nearly so, with strappy, succulent leaves that end in sharp points. Foliage tends toward a blue-green in hardier varieties and a gray-green in warm climate varieties. There are also some that are variegated with gold or white markings.
  • Flowers: When the plant matures, a tall, flower-stalk grows out of the plant’s center. The flowers are bell-shaped and long-lasting, in shades of white, yellow and green. For most agave species, once the flowers produce the berry seed pods, the plant dies.

Botanical Name

Agave

Common Names

Agave plants are generally referred to as agaves. Agave americana as the Century Plant and that common name is sometimes confusingly used for all species of agave.

Cold Hardiness Zones

Most agave plants are not frost-hardy, but there are some, like Agave parryi, that are reliably perennial to USDA Hardiness Zone 5. However, the majority of them are only hardy in USDA Zones 8 or 9 and up.

Light Exposure

Agave plants need a spot in full sun to partial shade. The hotter the climate is, the more shade they can handle.

Mature Size Of Agave Plants

There is a lot of variety in the size of agave plants. They can mature from a few inches tall to 20+ feet in diameter.

Agave Bloom Period

Agaves are grown for their dramatic foliage, not their flowers. That’s a good thing because they bloom only once when they are fully mature. That can be anywhere from 5 to 40 years. Agave plants tend to bloom earlier in cultivation than they would in the wild. Most plants die after flowering. However, there are usually small offset plants at the base that can be replanted.

Garden Design Tips for Agave Plants

One large agave is all that is needed to make a sculptural focal point. Just make sure there is plenty of room to walk around it, so no one gets stabbed.

They can also make a nice border grouping, either by planting several of the same species or a tapestry of different varieties. They are textural and sculptural and make a vivid contrast with other plants. Pairing them with ornamental grasses softens their hard edges.

In warm climates, agaves are popular around pools and patios. Their leaves don’t brown and drop frequently, and they stay attractive all year. A spineless variety, like the Foxtail Agave (Agave attenuata), is a safe bet around heavily used areas.

Smaller agave plants are excellent for containers, indoor or out.

Suggested Agave Varieties

  • Agave attenuata – A popular spineless variety also known as the Foxtail or Dragon-Tree Agave. It grows about four to five feet tall and a bit wider.
  • Agave parviflora – Leaves have white, graphic markings and curling filaments that give it a hairy look. It only gets about six inches tall and blooms in six to eight years with green flowers on a four-to-six ft. spike.
  • Agave tequilana azul – Weber’s Blue Agave is used to make tequila, in Jalisco, Mexico, but it is also a very attractive garden plant, reaching upwards of six ft. tall and flowering in six to eight years with a 15 ft. spike of yellow blooms.
  • Agave victoria-reginae – As the plant matures, the broad leaves cup inward, forming a dome. It reaches a height of about 12 inches. Cream flowers appear in 20-30 years.

Diagnosing and caring for ailing agave

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We stood next to the driveway studying a rather stunted Agave americana. Farmers would call this plant a “poor doer” because it’s never become established in that two-year old landscape. In fact, it may have actually shrunk in size. “I wish there was a book that tells me how to take care of these plants,” the client lamented.

He was right, I do need to help readers with these details.

So now that summer is almost here, with just the yearround residents in town, it’s a perfect time to explore plant diagnostics. I honed my skills by maintaining newly-installed landscapes for Rogers Gardens back in the early ’80s, figuring out why the plants weren’t doing well and either fixing the problem or replacing the plant.

Whenever I see an ailing Agave americana, the first thing I suspect is agave snout weevil. This cousin of the boll weevil loves this species of agave the most. The female weevil punctures the central cone of leaves and releases toxins before laying her eggs there. Toxins alter the plant tissues so the hatching larvae can better consume it. Once the larvae start feeding, they interrupt the moisture channels to the roots, cutting off this connection to the head. It gradually dehydrates until the leaves simply fall flat.

This poor doer agave showed signs of dehydration, which are rare. The center of all agaves should have plump firm skin, but when the base of the leaves develop deep wrinkles, you know it’s having a moisture problem. The key is figuring out the cause, not just alleviating the immediate symptoms because unless you solve the original problem, it will come back.

To help narrow down whether it’s a weevil or not, I inspect the central cone of the plant for signs of weevils. They puncture the skin leaving a small wound that may be just 1/8″ or less in diameter. That may be all there is to tell you weevils are inside.

But maybe that tiny nick in the skin of this particular agave was made by something else. Maybe the wrinkles are actually a sign of inadequate irrigation water. However, it’s rare to see agave dehydration at the end of spring because it’s an end of summer kind of problem. So I move the gravel out of the way to see and feel the soil to determine whether it’s getting water from the irrigation system.

Since this is only a two-year old landscape, I’m always suspicious of inadequate irrigation because sometimes end of the line emitters are shorted pressure or clog with particulate matter that is pushed to the furthest head. With really drought resistant plants, it can take a season or two for symptoms of difficulty to be readily apparent.

Because all container plants grow in a specialized soil mix, it can become very dry and resist absorption, particularly in the very center of the rootball. If the irrigation is right, it will saturate that organic potting soil which is able to hold a great deal of moisture. If it’s not right, the root ball dries out and so do the roots.

When the water delivery is pin pointed through drip irrigation, roots grow there and nowhere else. Roots of container grown plants further from this water delivery point dehydrate and die for lack of moisture. It takes time for those few roots within range of the emitter to grow large enough to support the entire plant, hence a delayed growth rate. But if the emitter is moved closer to the center of the plant where it moistens that nursery soil, then the rest of the roots can benefit as well.

Like a physician, diagnosis often depends on how the patient responds to a certain test action. In this case I instructed the client to flood the entire root zone of that agave with a slow running hose set at the base of the plant. Once the root ball is saturated along with soil immediately adjacent to it, the agave will take in enough water to plump itself up again within just a few days. Those wrinkles at the leaf bases will vanish. But if those furrows remain despite the flooding, you know the plant can’t take it up. The reason is likely weevil larvae have severed root from shoot.

Prognosis is poor; replace this plant with a non-succulent shrub since weevil larvae are now present in the soil and will infest any of its favorite succulent plant food plants installed there.

Why are the leaves on my agave turning black?

From: Austin

Question: Dear Mr. Smarty Plants- We have a ~5-year-old agave americana that began to have leaves turn yellow (to black in some areas) just this past spring (2008). A neighbor’s tree had started to overhang the plot it was in, putting it in substantial shade, so I cut away several large branches from the tree, thinking that lack of sun could be part of the problem. Is there anything else I can do?

Answer:

We really hate it when someone asks us about an obvious problem with a plant, and when we do research we are told this plant has “no serious pests and diseases,” which is pretty much what we got on your Agave americana (American century plant) spots. One thing we did find out, from our own webpage (link above) is that the Agave can tolerate light shade, but really needs sun. But, we did find two websites that admitted there could be anthracnose, a fungal disease, in agaves that could cause those spots.

Michigan State University Extension Agave Disease Problems

Arizona Cooperative Extension Problems and Pests of Agave — This is a PDF document, and you will have to page down to Page 6, lower right hand column, for “Fungal Lesions.” Anthracnose of agaves is discussed as a problem during moist conditions or occasionally when the garden is overhead irrigated, as in a sprinkler system or too much rain (hardly a problem right now in Austin). Unfortunately, a plant in too much shade will be more prone to fungal diseases because the sun would ordinarily retard the fungal production, drying out the moisture on the plant. The advice given for treatment is to remove the diseased leaves. And let us warn you, we have discovered that there can be severe and uncomfortable skin blistering from contact with the juices in the leaves when they are cut. Go prepared in long pants, long sleeves, heavy leather gloves, closed-toe shoes and maybe even protective goggles. Once a leaf has gone black, you can be pretty sure it is dead and needs to be removed and disposed in such a way as to prevent further spreading of the fungus to other succulents. This site did suggest one possible chemical treatment, but stated that its actual efficacy is not substantiated. We tried to find pictures of agaves with the anthracnose spots, so you could compare them to your plant, but were unsuccessful. In summary, more sun, less water, and cut out the affected leaves – VERY CAREFULLY!

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News

Originally from Mexico, the Agave Americana, also known as the century plant, is typically very hardy. It can live from 10 – 30 years; reach a height of 5-7 feet and a spread of 8-12 feet. It blooms once at the end of its life cycle where the stalk may reach up to 26 feet. The plant dies after flowering, but will produce shoots from its base.

The Agave Americana may look fine one day and show no signs of stress and quickly the base leaves begin to droop and curl under. Snout nose weevil infestations usually don%u2019t become apparent until much damage has occurred and it is too late to save the plant.

The adult agave snout nose weevils become active and remain active through the summer. The female weevil searches for a place to lay their eggs and will often seek agaves that are about to bloom, but can also attack non-blooming plants. The females chew their way into the plant base creating tunnels to lay their eggs. Their bite leaves a small dose of bacteria which quickly spreads and rots the plant. Later when the eggs hatch the larvae burrow and eat their way into the heart of the agave. As the larvae start feeding on the plant base and roots, the leaves begin to wrinkle and droop. Usually a majority of the leaves will fall to the ground and the central spike will remain standing. The damage is often fatal.

What to watch for: Wilting or curling leave, sparce growth, small holes in the leaves, and leaves that pull away easily from their base. You can try watering the plant several times to test for lack of water, if they do not perk up, chemicals are usually recommended. Control of the agave snout weevil is difficult.

Systemic insecticides with the active ingredient Imidaclorprid have been fairly effective in preventing and controlling infestations. It’s also suggested the Orthene (Acephate) may help in prevention. The product is injected around the base of the plant and is absorbed by the roots and carried throughout the plant.

Hi Tina,
Thanks for the link to the article you wrote, very nice, and I enjoyed reading it. You are truly a terrific ambassador for my very favorite of all the agave species. I have far more A. vic-reg than any other in my collection, not by accident, including all the different ones shown in your article with the exception of the crested. And you’re right, it is seriously odd-looking, but in a good way of course. By the way, I’m pretty sure that “Golden Prince” is a corruption of the name “Golden Princess”. Here is what I think is the actual correct information for that name : “Mary Irish proposed the name ‘Golden Princess’ in the Summer 2002 CSSA Journal (74:4) because latinized cultivar names given after January 1, 1959 are deemed not valid. This is a fitting name for this jewel. Tony Avent (Plant Delights Nursery), … now lists it as ‘Kazo Bana’. “
For various reasons, I find the general form of A. v-r extremely appealing. It’s so very symmetrical, and in that sense, very mathematically pleasing to behold. I once did a personal study of my first A. vr “White Rhino” after having grown it for several years, in which I labeled the leaves by order of appearance (I mean age), and measured the angles of each subsequent leaf in relation to a circle. Guess what? VERY fibonacci! I had posted labeled pictures on a certain plant forum with a table of measurements and calculations illustrating adherence to fibonacci sequencing, but unfortunately, I found out there are folks out there who don’t much appreciate math and science, I guess. I was told, that hands down, my post was the dumbest thing that particular agave grower had ever seen. He asked me, in satirical mockery, if he should bring a protractor with him whenever he visits a nursery! I would say, the point of my exercise escaped him entirely. In any case, I proved that that plant’s rosette does indeed follow fibonacci mathematical sequences, and while we may not be cognizant of that aspect when viewing the plant, it does indeed inspire an appreciation for an ordered beauty, even if one is particularly anti-math and science.
As you noted in your article, the medio picta forms are the slowest growing, and the reason is the same for the A. macroacantha variegated. Yes, warm temps (up to a point) improve the rate of chemical reactions going on inside the plant which ultimately convert sunlight to energy to growth. As with other CAM plants (Crassulacean Acid Metabolism), too hot or arid conditions may shut down the normal operation as the stomata may then stay closed at night (if it doesn’t cool down enough) to prevent water loss, in which case the carbon dioxide is recycled (cam-idling), which does maintain the plant, but limits growth. I don’t believe humidity is much of a factor, excepting if there’s too much moisture for too long, the possibility for rot may be increased. The reason for slow growth in medio picta variegation, whether A. victoriae reginae or macroacantha, is that the % of variegation is directly correlated to possible rate of growth. Where a green plant’s tissue contributes entirely to the function of the plant, variegated tissue lacks normal chloroplasts and as such add nothing to the function of the plant, in terms of actual photosynthetic activity. As such, variegated plants are somewhat inefficient, and rather handicapped compared to their green counterparts, leaving them with a hefty disadvantage competing in the wild. If they can survive, they are slow growing, and heavily variegated plants (such as medio picta) are thus very slow growing. Taken to the nth degree, an albino plant doesn’t grow at all, but dies shortly after germination, or in the case of an offset, after it’s removal from the mother plant.
Regarding the “ugly plant” – Hakuro Shiro Fukurin; in the same way that I find A. victoriae reginae beautiful for it’s order and symmetry, I find the A. difformis also beautiful for it’s seeming lack of those same qualities, giving an unruly appearance. It appears to me as a highly artistic form, with it’s irregular, twisty, undulating appearance. The bright white variegated edges contrast strongly as well with the pale green center, and irregular spines only seem to add to the overall appeal for me. I imagine it as a wonderful centerpiece on a table top.
I’m not sure if a low light situation for A. bracteosa would necessarily promote curly leaves, but it’s possible. Insufficient light does cause etiolation, and the leaves grow longer, the rosette less compact. I think it also stands to reason that the longer leaves may well have a tendency to curl, and that is definitely the case with my A. americana sport. I can think of a few other examples of long leaves becoming curly. One A. americana Medio Picta Aurea I have had long curly leaves at first. I had a great deal of difficulty getting it to adjust to partial sun, due to leaf burn. That same plant today, after slow acclimation to stronger light (took over a year of gradual increase of light) now has much more stout and erect leaves, and a much more compact rosette. I can also think of a couple of rather large examples whereby for genetic reasons (mutation), a very large and very long leaved agave also has curly leaves. One would be the sometimes ID’d plant as A. americana Marginata, or A. mapisaga Marginata, and another different plant I’ve found ID’d as A. salmiana Angustifolia Marginata (though not likely an actual salmiana). Anyway, I think one can make a case for excessively long leaves and a curling tendency. Here’s a shot of one of mine brought outside for a photo-op last year. It’s a rather large plant, and seems to enjoy it’s spot in the greenhouse, which is why I keep it there. Although it will get much larger yet, but seen surrounded by other plants in it’s current 5 gal pot, it is easier to appreciate it’s actual current size. I’ve had this plant since 2009, when it’s leaves extended out about double the size of it’s original one gallon pot. The leaves start out very straight and unlikely looking as they separate from the core, and then in short order flop over, and then curl at the ends. I’ve also noticed a tendency for some of the leaves to flop over naturally in the entirely wrong direction, leaving the leaves upside down, and without vigilant supervision and training of the leaves to flop over the “right” way, it would really take on an absurdly haphazard appearance.

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