One great thing about having a sago palm (Cycas revoluta) is that your kids, grandkids and great-grandkids won’t have to worry about it outgrowing its surroundings. These prehistoric conifer-and-fern hybrids take up to 50 years to reach 12 feet. A major drawback to having one is that it's toxic enough to cause liver failure in both people and animals. If you decide to work one of these tiny, exotic and dangerous charmers into your garden, be prepared to defend it from crown rot.
Suitable for growing outdoors in U.S. Department of Agriculture plant hardiness zones 9 through 11, sago palms tolerate some frost, but suffer damage below 23 degrees Fahrenheit. Temporary frostbite harm includes black-spotted fronds dropping from the plants. The real cold-weather danger occurs when frozen trunk tissue starts rotting from its damaged outer layer to its healthy inner ones. The rate of decay increases dramatically with the return of warm weather, so it's technically possible for frost damage to kill a sago palm in summer. You'll know your plant is in trouble if it has no new spring growth following a freeze.
Preventing Freeze-Related Crown Rot
A layer of mulch around your sago palm's trunk keeps its roots warm and prevents soil moisture from freezing. When the forecast predicts frost, bundle an in-ground plant in a frost cloth, which you can buy at a garden center. If you don't have frost cloth, a bed sheet makes an acceptable substitute. One of your home's outside walls -- preferably one with an overhang -- provides good shelter for a potted sago too large to bring indoors.
Fungal Bud Rot
Fungi -- usually Phytophthora palmivora or Thielaviopsis paradoxa -- may invade a sago palm's crown through the newest, smallest fronds and advance to the older ones. The faded, wilted browning fronds eventually collapse, pulling away from the crown easily to reveal decaying, brown, foul-smelling bases. Thielaviopsis rot may also invade the trunk. Only a laboratory analysis can determine which fungus has attacked your plant.
Preventing Fungal Bud Rot
Prevent bud rot fungi from getting a foothold by giving your sago palm well-draining soil, because these pathogens require moisture for spore production. Water carefully so you don't splash spores from the soil onto the plant. Weeds harbor insects that spread fungi and snails moving from plant to plant can also transport the spores, so schedule regular weeding sessions and snail-hunting forays with the kids. After pruning your palm, disinfect your pruning tools in a solution of 1 part bleach to 9 parts water.
Chemical Bud-Rot Control
Chemical fungicides are effective only on young sago palms in the earliest stage of bud rot. If your palm’s spear leaf -- its youngest, unopened frond -- pulls away without resistance, your only option is to remove the plant so it doesn’t spread the disease. For a plant diagnosed with Phytophthora, apply fosetyl-al foliar spray every three months for a year. Wearing protective clothing, socks and shoes, spray the fronds thoroughly with a solution 4 to 8 ounces of fosetyl-al concentrate -- or the manufacturer's recommended amount -- in 10 gallons of water. The only fungicide effective against Thielaviopsis, thiophanate-methyl, is an EPA-listed toxin.