Yucca? Agave? What's the difference? Many folks find it hard to tell one big round rosette of sword-like spiny leaves from another big round spiny plant.
The easy answer is they are all related, anyway. They are all kin to grasses and lack wood (a designation that also applies to palms). They all also grow in an elegant spiral, the crown forming a lovely rosette. The main thing to know is that agave, century plants, flower once then die, while yuccas flower every single year, and often live for years longer than agaves.
Yucca flowers are great. Produced in giant clusters of big, bold, creamy white flowers on tall stalks, the flowers open at night and last a number of days. Every night the base of each flower fills with nectar while they release a sweet fragrance to entice their favorite pollinator, the yucca moth.
Yuccas come in many different sizes, forms, and degrees of "stickeryness." Some have narrow pointed leaves, others have broad relaxed leaves. Consider what effect you are going for in your landscape before you plant one.
There are many ways to classify yuccas, but since this discussion is about them as pleasing landscape plants, let's look at their overall forms. These can be divided into four main groupings.
Tall trunk and branching yuccas with multiple branches. This group includes the famous Joshua tree (Yucca brevifolia) from the Mojave Desert. Joshua trees slowly grow to reach 30 feet high and 30 feet wide. For a more tropical look, choose the spineless yucca (Y. elephantipes), with bright green leaves; this plant also reaches 30 feet but only around 15 wide. Tropical indeed, it looks like it has been living in tropical Margaritaville. Not the right selection if you like tidy plants.
Tall trunk yuccas that don't branch very much include the soaptree yucca (Yucca elata), reaching 20 feet tall, with graceful green leaves. These make tidy, bold and striking accent plants. The roots are used for shampoo. Blue yucca (Yucca rigida) from the Chihuahuan Desert has upright silvery blue leaves. It reaches 12 feet and spreads its arms to five feet, and looks dramatic in a yard that has blue tones.
Short yuccas that form clumps with many heads include the very sharp Spanish dagger or aloe yucca (Yucca aloifolia) with individuals to 10 feet tall and five feet around. Mojave yucca (Y. schidigera) has olive green leaves which look nice with creosote bushes. Individuals generally reach around six feet tall and three feet wide.
Short yuccas that very rarely branch or pup but often get very big around include Our Lord's candle (Yucca whipplei), reaching three feet tall and six feet wide with striking, rigid, gray-green leaves. The pendulous yucca (Yucca recurvifolia) is a fast-growing yucca reaching six feet tall and around with softly recurved, faintly bluish leaves. The banana yucca (Y. baccata) also falls in this group, reaching three feet tall and five feet wide. Best of all, the banana yucca produces highly edible young fruit. Steamed, they taste similar to artichoke hearts.
Just remember that some of these yuccas can get very large, and plan your planting accordingly. The good and bad news is that most yuccas can not be pruned. The branching ones could have a limb removed if you wish, but yucca quickly die if their central rosette is injured. The practice of cutting off older dead leaves is also hazardous to yucca health. They need those leaves to shade their trunk. If you give an old dead leaf a gentle tug and it falls off, then that species can have its dead leaves removed. If it won't come off, "leaf" it alone.
Jacqueline has been writing about gardening in the Southwest for close to three decades. She is currently working on a book on growing and using the herbs of Father Kino's Mission Gardens.