Agave macroacantha (Black Spined Agave)

Agave macroacantha

Agave macroacantha, commonly known as the black spined agave, black tip agave, or black spine agave, is a medium-sized succulent shrub native to Mexico that features black spines and blue-green leaves. This slow-growing plant will mature to about 3 feet tall and wide over the course of several years; it can be pruned down to keep its size more manageable, if necessary.

Black Spined Agave are grown both indoors and outdoors in warm, dry climates; they do not tolerate cold temperatures or high humidity well, so they should be planted in warm, dry climates with good drainage.

Agave macroacantha grows naturally in Mexico and can grow as tall as ten feet when mature. The plant has fleshy blue-green leaves that range from five to twelve inches long and three to six inches wide and are typically widest near the end of the leaf stalk. The leaves taper at the end, which have black spines that may be up to three inches long and curve inwards toward the center of the leaf stalk.

The black spined agave is a species of agave native to Mexico and Guatemala, as well as being cultivated in South Africa and Australia.

Origin and distribution

Black spined agaves grow naturally in scattered locations in Mexico. The plant is grown by nurseries, which distribute them in many parts of North America. Black spined agaves are often planted as ornamental because of their dramatic foliage and black spines.

Despite its relative ease of growth, it has become a pest to people who garden because it tends to escape from cultivation and become invasive in areas where it is not wanted.

Black spined agaves prefer full sun and well-drained soil with little competition for water or nutrients. They tolerate temperatures down to 15 degrees Fahrenheit but will usually die if exposed to frost.

Agave macroacantha propagation

Agave macroacantha

Agave macroacantha can be propagated by division or seed, but they also spread readily through rhizomes that form on older plants.. This can be done at almost any time of year, although spring and early summer are preferable for large divisions.

YOU MAY ALSO LIKE:
Agave kewensis (Grijalva's Agave)

The cuttings should have at least one healthy leaf on them to survive their first season; try to avoid taking a cutting from an older part of a plant that may contain disease or parasites. Once rooted, a division will generally develop roots throughout its new body and become ready for transplanting in one to two years.

Plants grown from seed may take up to three years before they’re ready for transplanting. In either case, you’ll want to start your newly transplanted agave in a well-drained potting mix with plenty of light and water.

It is important not to overwater young plants as they are more susceptible to root rot than mature ones. If you do overwater your young plant it will likely lose most if not all of its leaves.

Agave macroacantha care information

Agave macroacantha

Black tip agaves require little care beyond light pruning in late winter to remove brown or damaged leaves. Black tips can be propagated from division or by seed. Seeds should be planted immediately in well-drained soil as they are slow to germinate and grow. Division should be performed during repotting as new heads will not appear on old plants.

Light requirement

Agave macroacantha love to be exposed to full sunlight, or at least six hours of bright light a day. If you don’t have a spot for them in your home with lots of light, consider moving them to an outside patio or even outdoors if it gets hot and sunny enough during the summer. Just make sure they’re getting plenty of sunshine or else they won’t grow.

Soil/potting mix

Agave macroacantha like to be in well-drained soil that doesn’t remain too wet for too long. However, if you live in a climate with frost or below-freezing temperatures, make sure you provide your black agave with some protection from freezing temperatures. Because of their slow growth rate, they are not heavy feeders.

They do best in soil that is 50% sand and 50% compost or other organic matter with a pH of 5-7.5. If you want to use fertilizer, look for one with low nitrogen and high phosphorus numbers such as 10-10-10 or 20-20-20. If your potting mix does not contain enough nutrients on its own, fertilize sparingly once every two months during spring and summer.

In fall and winter when growth slows down, fertilize once every four months. Water regularly but don’t overwater; keep the soil lightly moist at all times but never soggy.

YOU MAY ALSO LIKE:
Agave colorata (Mescal Ceniza)

Watering

It is essential to keep Agave macroacantha well-watered, but not drowning. Overwatering can cause root rot and fungal disease. You should be watering your plants once or twice a week, depending on how hot it is and if there are any extended periods of rain or lack thereof in your area. If you’re able to touch your finger down into soil without seeing dry earth or white powder you’re good to go with watering that plant.

Fertilizer

To keep it healthy and strong, feed agave macroacantha approximately 2 times per year with fertilizer that contains adequate levels of nitrogen, phosphorus and potassium. Keep fertilizer at least 6 inches away from the plant.

Over-fertilizing can burn plant’s roots. In addition to using fertilizer in garden soil, add slow-release pelletized fertilizer around the base of the plant for supplemental feeding. Do not use chemical fertilizers or herbicides on agave macroacantha. It is possible to kill your plant if you do so!

Temperature

The ideal temperature is 65-85 degrees Fahrenheit, 21-29 degrees C. In warmer areas, allow plants to dry between watering. In cooler areas, keep plants moist. Plants grown in low light will require more frequent watering. Under ideal conditions, plants may survive a few days without water, but expect the loss of leaves when under drought stress; it’s best to water as soon as you notice your agave looking less than vibrant.

Humidity

Because of its soft succulent leaves, Agave macroacantha thrives in areas with low humidity levels. The ideal home for these plants is one with a relative humidity that hovers between 40 and 50 percent. Without enough moisture in your home, Black Spined Agaves will likely become stressed and are more prone to disease. Mist your plants daily, or opt for houseplants that thrive in dry environments instead.

Pruning

Any time you prune, wait until after it’s flowered so you’re not disturbing an agave flower. The two basic ways to prune are by shearing and by removing a portion of a branch. Shearing works best for small plants, and can be done with hedge shears or hand pruners; remove any leaves that may be in your way as you go.

YOU MAY ALSO LIKE:
Whale's Tongue Agave (Agave ovatifolia)

When using hand pruners, cut at a 45-degree angle just above a leaf node. When cutting back larger branches, use loppers or saws. Make sure to sterilize tools between cuts to avoid spreading disease from plant to plant.

When to repot

Agave macroacantha

Transplant an Agave macroacantha when it has outgrown its pot. When you buy your plant, choose a shallow container that is only slightly wider than its current root ball, and place it in a sunny location.

If your Black Spined Agave gets too big for its container before needing to be repotted, you can replant it in a deeper pot and then move it back to a shallow one once its roots have filled the new planter. The general rule of thumb is to wait until it’s about two-thirds as wide as its current pot before transplanting; if you notice that your plant’s leaves are curling or browning at their tips, however, it may need repotting sooner.

You should also check on your agave regularly throughout the year and make sure that it doesn’t look like its suffering from over or under-watering; if so, adjust accordingly.

Dormancy/Winter rest

During the winter, or any time when it’s too cold to grow and/or set seeds, Agave macroacantha go dormant. This means they look pretty much like a dead plant for several months at a time. The leaves wither and die and often fall off completely, but don’t worry, that just means it’s sleeping!

When spring returns, agaves burst into new growth again. If you want your agave to flower and reproduce, make sure you provide it with plenty of water during its dormancy period.

If you live in an area where temperatures drop below freezing during winter, consider moving your agave inside if possible; otherwise, expect some browning on your plant as temperatures dip below 40 degrees Fahrenheit.

Agave macroacantha flower & fragrance

The fragrant white flowers of Agave macroacantha, up to 3 inches long with violet buds that open pale pink, are born in late spring on arching flower stalks that rise above an individual rosette. The black spines, which can grow up to 8 inches long, cover each leaf rosette and have sharp tips. When you touch one of these spines, it will cause your skin to secrete a white milk-like substance that contains proteolytic enzymes used for self-defense.

YOU MAY ALSO LIKE:
Agave angustifolia (Caribbean Agave Plant)

Growth rate

Agave Macroacantha is a quick grower with a growth rate of 1-2 feet per year. They do best in full sun and very well-drained soil, and are drought tolerant once established. Water only when wilting and allow the soil to dry between watering sessions, but never let it completely dry out. This plant is particularly susceptible to root rot if overwatered or planted in poorly drained soils.

Toxicity

The sap from plants is toxic due to the presence of rotenone, a chemical found in various genera of plants, including members of e.g. genera Oncidium, Philodendron, Colocasia, and Manihot.

It is used as an insecticide and is also thought to have been used by indigenous peoples of Brazil to poison arrows used for hunting. The toxin can be fatal if ingested in high doses; it causes severe gastrointestinal irritation with vomiting and diarrhea being commonly observed symptoms.

USDA hardiness zones

Agave macroacantha thrives best in USDA hardiness zones 9 and 10. In colder areas, it’s possible to grow an agave as a houseplant, but you’ll need to provide it with plenty of light and warmth.

It’s also important to note that agaves don’t like being moved around too much once they are established, so it may be easier to start your black spined agave from seed or a cutting if you live outside its ideal climate range.

Pests and diseases

As is common with succulents, Agave macroacantha are susceptible to pests and diseases. In northern climates, Agave snout weevils, mites, and leaf miners are all threats to your Black Spined Agave. A systemic insecticide or biological control like parasitic wasps can be effective.

Scales, spider mites, and mealybugs can also attack Agave macroacantha. Remove pests with a light hosing of water or spray them off of your plant with an insecticidal soap made for houseplants.

Conclusion

The Agave macroacantha is one of many species which has beautiful and intricate spines to help protect it from predators, making it a plant you can be proud to have in your home or office. While not native to North America, there are many other agaves that are just as beautiful, though these are much more suited for indoor environments. Which plants have you grown indoors? What have you learned about them? We’d love to hear from you!