This column is for the novice growers interested in dipping their toes in the deep fascinating ocean that is Haworthia. By haworthia, I am referring to the "window" haworthia. For many years the term Haworthia was associated with common hard leaved haworthia, like H. attenuata "Zebra plant". Those plants are now considered to be their own genus "Haworthiopsis," and are no longer considered haworthia (for more, see my previous blog "What is and what isn't a Haworthia"). The "window" haworthia are slower and more challenging than their Haworthiopsis cousins.
"Are Haworthia difficult to grow?" I get asked this question a lot. The answer I always give to this question is "No, BUT they have certain requirements that need to be met to keep them healthy and looking nice." Haworthia are certainly easier and less likely to suddenly die on you than some other ornamental succulents such as lithops.
"How big will it get?" is another question. Usually the answer is: "Not much bigger".Their small size is an advantage - they don't take up much room. Haworthia compete with the lithops as being the reigning unusual African succulent miniatures. Lithops are more unusual no doubt. But haworthia are more beautiful in my opinion.
"Do haworthia make good house plants?" Haworthia love to live in greenhouses, especially ones with good cooling systems. But, until last year, all of my haworthia were kept outdoors in my home in Northern California, where they looked great. Haworthia make good houseplants if certain requirements are met.
Requirements for good growth:
Soil: my favorite mix for haworthia is pumice (a volcanic rock, not to be confused with perlite or red lava rock, which are not as good) with just enough coir (a coconut-based soil) to keep it from drying too quickly, plus a touch of decomposed granite for mineral nutrition. Artisan Plants sells a high quality soil mix perfect for haworthia. See here for more information.
Temperature: Haworthia don't like too much heat or too much cold. If it's above 85 degrees F or 30 degrees C they go dormant. If it gets above these temperatures, move them into shade and don't water them too much. Haworthia can tolerate temperatures around the freezing point, but I've noticed they are not happy if the temperature dips to or below the freezing point for too long. In general, I have noticed that if Haworthia are too hot they will lose their roots because of rot; If they are too cold, the outer leaves rot.
Light: Morning sun is best. In my home, my haworthia get morning sun with shade starting around 11 AM. Hot noontime sun will burn haworthia.
Water: I water haworthia about once every 1 to 2 weeks all year. Water pH can be an issue. Most tap water is intentionally alkaline to prevent corrosion of pipes. But almost all plants like slightly acidic conditions. You can add a tiny bit of white wine vinegar (1 teaspoon or 2 per gallon of water) or use a commercially available pH adjusting kit (I use the General Hydroponics kit) to adjust your water to a more plant friendly pH. Fertilizing will usually lower the pH into the plant friendly zone as well.
Indoors vs. Outdoors. If you live in a place like California where the winters are mild, you can grow haworthia outdoors all year. If you live in a climate with snowy freezing winters, you will have to either put them in a greenhouse or keep them indoors over winter.
Growing haworthia indoors. What do you do if you are in a snowy cold winter climate and bring your haworthia indoors during the cold months? Will Haworthia be happy indoors over the winter? What if you live in an apartment in Manhattan and have no outdoor space? Can you still grow haworthia? I've never tried, but the answer is yes if you address two factors: light and air circulation. Haworthia need good light, otherwise colorful haworthia will turn boring green and stretch out to become spindly. If grown indoors, supplemental lighting may be required, especially over the winter, to keep haworthia looking compact and healthy. These days, there are many options for supplemental lighting, including the classical cool white fluorescent lights and newer LED lighting systems. I wish I could offer more guidance to specific systems but I don't have enough personal experience. I can point people to conversations on Facebook where this issue is discussed, however. The other important factor is air circulation. Haworthia need good air circulation to thrive. It's as important a factor as anything else and can be addressed with a simple inexpensive fan. Air circulation makes a HUGE difference in the growth rate of haworthia.
Fertilizer: I mix a small amount of slow release fertilizer into my soil mix, and also add decomposed granite which provides minerals. These days, succulent growers can take advantage of all of the hydroponic stores that cater to the Cannabis growers. They have an amazing range of fertilizers, grow lights and other useful products. I fertilize my haworthia with General Hydroponics 3 component mix which provides all the nutrients plants require. I also occasionally use a silica fertilizer. Silica has been linked to increased resistance to pathogens. When using silica fertilizer, you must monitor pH carefully as the silica will increase pH quite a bit.