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For The Garden

Living Stones

Author: Cathy Cromell
Issue: November, 2012, Page 73
Photos by Richard Maack

Doug Dawson (above) grows a variety of unusual desert plants in his greenhouse, but his favorites are lithops, also known as living stones.



doug dawson fulfills his passion for plants, rocks and geometry in a backyard greenhouse

As a mathematician, Doug Dawson is drawn to the geometric shapes of cacti and succulents, and grows thousands of them from seed in his Ahwatukee, Arizona, garden. He is fascinated by Lithops, a genus of succulents commonly called living stones. “Most lithops mimic the rocks and pebbles they grow among in their native habitat in South Africa, Namibia and a small area of Botswana,” he explains.

Dawson travels to these areas annually to observe lithops in their natural settings. “They grow in gravel fields, often with a lot of quartz strewn about,” he relates. “At first, it’s difficult to see lithops because they blend into the surface, but after a while you develop a mind-set for the hunt, and they become easier to spot.”

Lithops display muted colors—tan, brown, gray, green, orange, rust and rose—with intricate markings on their tops. They are small (about the size of a dime or quarter), with a crease down the middle that splits the plant to form a “leaf pair” with almost no separation between the succulent halves. “Each spring, the old leaf pair begins to shrivel, the crease splits open, and a new pair emerges,” explains Dawson. The new pair obtains its energy to develop from the old, until the old eventually withers to a bit of gray tissue resembling dried onion skin.

Pictured in the pot above are blue-hued Lithops schwantesii var. urikosensis ‘Nutwerk’.
Dawson notes that a neat feature about this life cycle is that a damaged lithops will be renewed. “For example, a cactus that is pecked by a bird will always display that scar, whereas a bird-pecked lithops will be brand-new next year.” In Dawson’s yard, birds make it unmanageable to grow lithops outdoors, as they like to peck at the succulent plants. Most of his collection is safe in his greenhouse or shade house, although he devised a protective method to experiment with some outdoor pots. “I poke bamboo skewers into the pot to confuse birds and prevent them from landing. Sunlight is still able to reach the plants through the skewers.”

GROWING LITHOPS
Observing lithops in their natural African surroundings has helped Dawson to grow them successfully in Arizona. Lithops do not like “wet feet” and will rot if soil is too moist. “Examine each plant,” he advises. “If there is any horizontal wrinkling on its side, give it a small drink— just enough water to soak down one inch. I water year-round, about every two weeks, but never drench the soil. Also, lithops are fresh-air fiends, and good air movement seems to help prevent them from rotting.”

Summers in the low desert can be tough on lithops, especially if they are over-watered or monsoon rains soak the pots. “Really hot temperatures plus wet soil equals mushy lithops,” observes Dawson. Corrugated fiberglass rooftops on his greenhouse and screen house prevent monsoon rains from soaking his plants. Even so, our intense heat is too much for some lithops species, such as rosy-hued Lithops optica rubra, so he transfers them into his home during summer.

Photos - Clock-wise from top left: Described as exhibiting the color of red wine, Lithops salicola ‘Bacchus’ offer up a range of purple and green-blue hues. • The markings on the tops of lithops help camouflage them in the wild from foraging animals. Pictured here are Lithops aucampiae subsp. euniceae. • Doug Dawson holds a pot of Lithops hallii ‘Green Soapstone’. He uses tweezers to remove plant debris. • The intricate markings and unusual orange tops of Lithops karasmontana ‘Summitatum’ are characteristics collectors find desirable.
 
RED CUP SOCIETY
Through trial and error, Dawson determined that lithops he starts from seed have better survival rates than plants shipped to Arizona from California growers. “Imports from dissimilar growing conditions are not prepared for our blast of summer,” he says.

With a tongue-in-cheek play on the Red Hat Society, Dawson refers to his successful method of seed germination as the Red Cup Society. He uses plastic disposable cups as containers and cuts the tops off of plastic soda bottles to fit snugly as “hats” for the cups (see Starting Lithops from Seed, Page 78). “The advantage of this method is that it maintains moisture, so I don’t have to spray throughout the day, as a nursery would,” explains Dawson. “Like any other type of seedling, if you miss watering and it goes dry, even a succulent will die.”

The gardener’s “Red Cup Society” holds many plants he started from seed.
In the Phoenix area, lithops bloom October through December with white or yellow flowers. Dawson hand-pollinates them to selectively breed plants with intense color or glitzy markings. He positions small artists’ brushes conveniently in pots around the shade house and greenhouse, so as flowers open, he is ready to brush pollen from one to another. “There are about 40 species of lithops, and many subspecies and varieties. So there’s no end to what you can do to create variation, just like hybridizing roses or other plants,” he remarks.

“I used to collect rocks, and I’ve always liked plants, so what better plant for me to grow than living rocks,” observes Dawson. “Lithops display such genetic diversity that it’s like rock collecting in my own greenhouse.  

LEARN MORE
If you are new to cactus gardening, or would just like to learn more about it, consider attending a Central Arizona Cactus and Succulent Society meeting. The monthly events include a speaker, Q&A sessions, how-to demonstrations, plant giveaways and more. Meetings are held the last Sunday of most months at 2 p.m. at Desert Botanical Garden in Phoenix, dbg.org. Guests are welcome. Find details at centralarizonacactus.org.

Photos - From left: Doug Dawson photographed these lithops on a trip to South Africa. Lithops
otzeniana
(above left) was photographed in Northern Cape. A flowering Lithops optica (above right) was shot in its natural habitat on the Namibian coast.

STARTING LITHOPS FROM SEED
Sow seeds in October, which allows plants to develop to sufficient size before the summer heat. Doug Dawson sows seeds in “mini greenhouses” created with plastic disposable cups and the tops of clear plastic 2-liter soda bottles. (Plastic cups maintain more consistent soil moisture than terra-cotta or ceramic pots, he says.)

1. Poke 8 drainage holes in the bottom of each plastic cup.

2. Pour in sand to a depth of 1 inch.

3. Fill cup to within 1 inch of its rim with soil mix for succulents. Dawson creates his own using 2 parts sand, 2 parts pumice and 1 part desert soil (without clay). Never use clay soil or commercial mixes with lots of organic matter for lithops,” he advises. “Both retain moisture and promote rot.”

4. After filling, wipe down the cup’s exposed interior to remove dust. Top off with 1/2 inch of very fine, sterilized soil mix that is lightly moistened.

5. Distribute 50 to 60 of the tiny seeds over the top of the soil. (Visualize one sesame seed as being equal to about 20 lithops seeds to help with measuring.)

6. Scatter a thin dusting of fine sand on soil surface for seeds to nestle in.

7. Set the cups in a water bath about 2 to 3 inches deep for at least one hour or overnight. Water will be absorbed into the soil through the drainage holes.

8. Place the soda bottle dome, with screw-on cap tightly closed, over the cup.

9. Set your planted cups in filtered light, but never in direct sun, which will “cook” them. Seeds should germinate in four to 14 days.

10. A few weeks after germination, remove the screw-on cap. Sprinkle fine gravel, water  seedlings, and replace the clear dome. In a few months, remove the dome completely. Allow seedlings to grow for nine to 12 months before transplanting.
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