Why Are My Sago Palm Leaves Turning Yellow?
Beautiful in the landscape and in containers indoors and out, sago palm trees produce a crown of whorling evergreen leaves. Each long leaf holds symmetrical leaflets, giving them a feathery, fronded appearance. The tropicals thrive in warm climates and also make easy-care houseplants.
Sagos aren’t true palms but cycads, belonging to the ancient family Cycadaceae and more closely related to pines and spruces than palms. Cycads pre-date the dinosaurs and even served as a food source for the prehistoric herbivores. Longlived and low maintenance, today’s sago palms make an elegant accent along foundations, in shrub and perennial borders, and as container features.
While mostly problem-free, sago leaves turning yellow is not uncommon. Yellowing is a sign of stress resulting from imbalances in key growing conditions. With a few adjustments, the enduring specimen can return to its crowning glory.
About Sago Palms
Originating in Japan’s subtropical southern islands, Cycas revoluta lends a tropical flair and contrasting texture among other broadleaf plantings. The islands are humid and sunny, with rainy seasons and typhoons. They experience warm summers and cool, moist winters. Outside their native environs, they’re hardy in USDA zones 9-12.
Sagos are very slow-growing, taking several years to reach a few feet tall and wide and 50 years or more to reach a maximum size (eight to ten feet). Some of the oldest species are over 200 years old. They stay small in containers and in bonsai applications. The cycads boast Royal Horticultural Society Award of Garden Merit status for their all-season appeal, minimal maintenance requirements, and pest and disease resistance.
In sago palms, some yellowing leaves are normal as they mature. Young plants produce leaves intermittently, but mature selections only produce one per year. As lower fronds age, they stop absorbing nutrients and make way for new upper growth. Let yellowing fronds remain in place until they completely turn brown. These continue to absorb nutrients and photosynthesize for the core. Prune to remove dead brown fronds anytime.
Sagos contain cycasin and are toxic to people and pets if ingested, especially the seeds. Use caution in placement indoors or out with children or pets nearby, and use gloves when working with the spiny-tipped leaflets.
Too Much Sun
For sago palm trees growing in full sun, harsh direct rays, especially from the afternoon sun, can damage foliage. Sunscorch can damage tissues, causing leaflets to yellow, brown, and fray.
The tropicals thrive in bright, indirect sun and partial shade (four or fewer hours of sunlight daily). Locations where they get morning sun and filtered afternoon light in hot climates are ideal.
Indoors, place them near a sunny window that receives four to six hours of filtered light (like through a curtain) and rotate the plant occasionally for even exposure. They adapt to less light, but plenty of bright, indirect light is best.
Manganese Deficiency
Manganese deficiency is a leading cause of sago leaves turning yellow. The deficiency is common, especially in more alkaline soils. Causes are a lack of the micronutrient in soil, poor drainage, alkaline soils, and under or overwatering.
A lack of manganese presents as yellow or brown streaks or spots on leaves, and they may yellow entirely. New growth may distort, stunt, and quickly turn from yellow to brown. Growth on the upper portion of the plants may dieback completely. The fronds take on a frayed, frizzy wear.
Manganese is a micronutrient necessary for all plants and is most available when soil pH is between 5.5 and 6.5. Sagos thrive in acidic soils and rely on it for healthy growth. Fortunately, this problem is easy to correct. Amend with palm fertilizer or manganese sulfate (different from magnesium sulfate in Epsom salts) if signs point to a deficiency.
Other Nutrients
Sagos don’t usually require additional fertilizer in the landscape. If you have lean soils and want to boost nutrition, opt for a palm fertilizer in spring or early summer. While cycads and not true palms, the nutritional requirements are similar. The same holds for potted specimens, where a granular or liquid feed may support growth in the warm months.
Sandy, humusy, and well-draining soils create an ideal foundation. Good drainage is essential to healthy roots. In containers, opt for a high-quality mix amended with sand or perlite to promote drainage (or a formula tailored to palms).
Add compost at planting, especially in poor soils like clay and sand. Compost helps with aeration, moisture retention, drainage, and nutrition.
Alkaline Soils
Sagos do well with a neutral to slightly acidic soil pH of around 6.5-7.0. Alkaline soils have a pH higher than 7.5 and contain sodium carbonate, raising the pH and limiting access to micronutrients like iron, manganese, zinc, and macronutrients like sulfur. Iron chlorosis is common in alkaline soils.
Alkalinity blocks root access to nutrients, leading to yellowing leaves and a lack of vigor. A soil test helps determine pH levels and helpful amendments, like garden sulfur, to lower alkalinity and raise acidity.
Watering Issues
Fluctuations in water are another cause of sago leaves yellowing. Overwatering damages the roots and leads to their inability to uptake water and nutrients necessary to support growth. Underwatering causes the plant to conserve energy and direct moisture to sustain roots and foliage.
The island growers prefer regular, even moisture but are drought-tolerant once established. While they tolerate occasional flooding in fast-draining soils, the cycads have a low threshold for prolonged periods of standing water. Overly wet soils can lead to root rot, and they’ll wither in saturated situations. Other than manganese deficiencies and sun exposure, excess water is a top cause of yellowing.
As houseplants, they withstand drying out slightly between waterings. Indoors, water plants thoroughly when the top inch of the medium feels dry to the touch. Stress during dry spells causes leaves to discolor and invites pests like spider mites.
For those growing in containers, make sure the pots are well-draining. Check on moisture often during the warm season since they dry out faster than ground soils. Reduce watering in the fall when the active growing season slows and when containers move back inside. Water in the winter only when the soil feels dry to the touch to a depth of an inch (every three weeks or so as needed). Use room-temperature water during each session to avoid shocking the roots.
Cold Damage
Sagos are hardier than some true palms but may suffer injury during cold snaps and frosts. They withstand short dips into the upper teens, but temperatures below 15°F (-9°C) risk survival. With cold and icy conditions, they may show frost damage through yellow and browning tips and stems.
Mild, warm environments offer the best conditions, with ideal temperatures between 65-75°F (18-24°C). In the landscape, sago palms benefit from a mulch cover to regulate soil temperatures, provide insulation, retain moisture, and suppress weeds. Pine straw, bark chips, or leaf litter make good mulch materials. Pull the mulch layer away from the trunk to prevent disease issues.
Potted houseplants enjoy summers outdoors in high shade or dappled light. Bring them in before temperatures drop in the fall for an easy transition to indoor conditions.
Low Humidity
In addition to warmth, their natural island settings are high in humidity. In dry air, leaves may become patchy and brown. Keep indoor specimens away from heated or cooled drafts that lead to excess drying.
Normally, average household humidity levels are fine. The ideal humidity for sago palms is around 30-50 percent. In drier conditions (winter can bring seasonal variation as we heat spaces), place pots near a tray of pebbles filled with water to raise surrounding air moisture.
Pests
Discolored leaves are a tell-tale sign of a problem, whether as minor as a watering misstep or indicating a bigger issue. Double-check the light, watering, nutrient, and temperature conditions to get to the bottom of changes. In addition, scout for pests.
Cycad Scale
Cycad scale (Aulacaspis yasumatsui) pierce leaves and stems to feed on sap. They have a waxy white armor and usually appear on the undersides of leaves and stems. They favor sagos and can cause detrimental damage.
An initial sign of cycad scale is leaves with yellow blotches. Fronds die back in heavy infestations. New growth may stunt or show deformities, and leaves may appear crusty and white in inundations.
Spray leaves and stems with water early in the day to displace the pests. For a small number of scale on houseplants, follow up with a cotton swab treatment. Dip the swab in isopropyl alcohol and wipe the stems and leaves. This treatment instantly reduces early numbers.
Horticultural oils like neem are treatment options for more severe cases. They may need repeat application to fully rid the plant of scale.
Mealybugs
Mealybugs are soft-bodied and look like little tufts of white cotton or dust on leaves and stems. In an infestation, you’ll see the insect accompanied by yellowing, wilting, and stunted leaves. They feed on sap and lay eggs in cellular tissues. Mealybugs also leave behind a signature sticky honeydew that can lead to black, sooty mold.
To prevent mealybugs, aim for consistent moisture. Avoid overfertilizing, as many pests enjoy tender new growth and high nitrogen levels, and excess fertilizer promotes both.
Use the stream of water method to displace mealybugs. Employ the cotton swab and alcohol rub for early numbers. Horticultural soaps and oils are effective in controlling nymph populations.
Spider Mites
Spider mites are tiny sap-suckers that live on the undersides of leaves. You may not see the tiny insects without a magnifying glass, but their fine webbing on stems and leaves gives them away.
Colonies live near leaf veins and mid-ribs underneath leaves. The females lay eggs, and the larvae hatch to quickly feed on sap and tissues. Adults feed and produce the tight webs.
With spider mites, foliage shows pale spots, light yellowing, and white stippling on surfaces. Leaves become stiff and curl, leading to early drop. Spider mites occur most in warm, dry, and dusty conditions. Specimens that experience drought stress from underwatering are most susceptible.
If you detect spider mites, use the stream of water method. As with scale and mealy, a horticultural soap or oil helps mitigate large populations.
Needs Repotting
The slow-growing cycads perform beautifully in containers and seldom need repotting. They prefer to be slightly root-bound to produce new shoots.
Every few years, refresh the potting soil. If exposed roots are visible through drainage holes or popping up above the surface, move them to a bigger container. Being too crowded limits roots in nutrient and moisture uptake, and yellowing leaves and a lack of vigor can be signs. A well-draining potting mix is essential, and one for palms or cacti works well.