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The Sago Palm isn’t a palm. It’s a cycad. That’s why it makes a terrific houseplant. It copes fine without extreme humidity. Give it bright light, take care when watering and it’ll grow just fine.
It won’t grow fast because these just never do. Even under perfect conditions, you’ll only see it grow by a couple of inches annually.
Naturally, with a such a slow growing tropical (ish) plant, when you see any of the fronds yellowing, that’s worry sign and one you need to investigate and fix quickly.
The biggest problem is that there’s just so much stuff that can cause the fronds on a sago palm to turn yellow. To find out what’s causing it, you need to play detective by going through a process of elimination to find the culprit, fix it, then nurse your sago palm back to health.
Discover the Causes of Sago Palms Turning Yellow
The biggest culprits that cause the yellowing on sago palms are nutrient deficiencies, waterlogged soil, cold damage, and acidic soil. When the soil’s too acidic, the plant struggles to absorb nutrients, which shows as foliage discoloration.
Asides from the growing conditions being inadequate, a host of insects can stress the plant so much that it causes yellowing on sago palms.
Identifying Nutrient Imbalances with Sago Palms
1 – Manganese
When the soil lacks manganese, the newest leaves turn yellow signaling the start of an early demise. The giveaway sign is when the yellowing starts as spots and streaks, then all the foliage turns yellow. The yellow fronds gradually turn brown, which is when they’re essentially dead.
The problem is the soil being too acidic. Higher than a pH of 5.5, and the roots can’t absorb the nutrients.
The fix is to apply a good dose of manganese sulfate to the soil. How much to apply depends on the size of your plant and the soil acidity. For a relatively small plant in acidic soil that doesn’t have drainage issues, an ounce of manganese sulfate watered in with a half inch of water should work.
Don’t confuse manganese sulfate with the similar sounding product magnesium sulfate. They’re two different things.
2 – Magnesium
A magnesium deficiency isn’t as serious of a threat as soil lacking manganese. Without enough magnesium, the damage is cosmetic. It won’t kill a sago palm, but the green can’t be restored either. You need to prune away discolored leaf parts for new healthy leaves to grow in replacing them.
A classic symptom of magnesium deficiency is marginal chlorosis on mature fronds on a sago palm. The center of the frond will keep its greenery with the yellowing contained to the leaf edges only.
3 – Nitrogen
Nitrogen deficiencies are more prevalent in landscape sago palms. Indoor container grown sagos don’t need all that much nitrogen in the fertilizer. It does need to be slow-release form though.
It should be noted that a nitrogen deficiency alone won’t turn the leaves on a sago palm yellow. Instead, it’ll be a pale light green that’s almost yellow. It looks like yellowing, but the fronds keep a lighter shade of green than normal.
It’s tricky to pick up on because it looks like yellowing that never actually goes yellow.
4 – Iron
Iron chelates is something you need to feed sago palms on occasion to prevent an iron deficiency. Most cycad fertilizers have this. When they lack iron, chlorosis can set in.
When it’s caused by a lack of iron, young leaves turn yellow and on the mature leaves, you’ll notice interveinal chlorosis – the leaves stay green but the leaf tissue surrounding the veins turn yellow.
The longer it continues, the tips of young leaves turn brown.
Acidic Soil Prevents Fertilizers from Working
Before you run off to your local garden store to buy lifeline supplies of iron chelates, manganese sulfate or any cycad fertilizers, check your soil first.
When the soil is too acidic, it’ll prevent nutrients from being absorbed by the plant’s roots.
The soil pH for sago palms should ideally be maintained between 5.5 and 6.5. When the pH is too acidic, like having a pH of 5.0, it won’t matter how much nutrients you put in the soil. The roots won’t be able to absorb it.
You need to know the soil acidity. To test it, garden stores and most big chain retailers, including Amazon.com have super cheap DIY soil test kits or digital meters that’ll give you the readings you need.
Once you know what you’re working with, then you can make adjustments to the soil to increase or decrease its acidity.
Quick tip: If you use a garden incinerator to burn pruned branches, wood ash is an abundant source of calcium and it’s rich in potassium, magnesium, and phosphorous. Work some wood ash into your compost, then work a small amount of that compost into your garden soil to decrease its acidity.
Ideally, soil testing should be done every two to three years, because as materials break down, fertilizer gets added, and the roots become more established, the nutrients in the soil will degrade.
To prolong your soil pH, it’s helpful to know how to organically lower the pH in water, because naturally, the more chemicals are in the water you hydrate your plant with, the worse an effect it’ll have in your soil.
Scale Insects: Nature’s Biggest Miniature Threat to the Sago Palm
Sago palms don’t attract too many insects, but the ones that do find them tasty for the sap in the leaves, congregate in triple digit numbers doing extensive damage fast.
Scale insects do the worst damage, sucking the sap from the fronds and stems, causing yellowing, browning, and eventually stunting growth. For a plant that only puts on two inches at most per year, you can’t have anything threatening that.
The most common scale insect to infest the sago palm are mealybugs. There is another pest that’s a frequent visitor to sago palms grown outdoors, and that’s the Asian Cycad Scale (Aulacaspis yasumatsui).
Mealybugs will typically eat the sap from the leaves. The Asian Cycad scale is similar in size and looks, but it’s tougher to evict because it infests every part of the plant. Leaves, seeds, cones, and roots. No part of the sago is immune.
When these get a start on your plant, they cause yellow spots on the leaves, sort of like what you’d see if bleach was sprayed on the leaves from a distance.
As these are both scale insects, contact miticides like neem oil are effective at killing them. Other insecticidal soaps can be used for coating the leaves, too.
As these feed on the sap, and lay eggs, not to mention ants coming in to farm them, essentially protecting them so they keep on eating your plant to poop out honeydew for the ants to eat, you need to repeat treatments.
Rinsing the leaves in the shower or under a tap can knock the mealybugs off. Washing the leaves with insecticidal soap gets rid of the sticky residue (honeydew), deterring ants.
If you’re growing your sago palm indoors and notice insects, or what looks like their eggs on the leaves, refer to: how to get rid of bugs on indoor plants.
Temperature Fluctuations that Cause Sago Palm Leaves to Yellow
In the midst of the summer, the fronds can get sunburned. When the yellowing is caused by too much direct sunlight, you’ll see patches of yellow, perhaps some browning of the leaves, too.
The simplest of fixes is to give the plant some partial shade. Perhaps put it under a taller plant so that it benefits from dappled sunlight rather than full-on direct sunlight.
Whenever there’s a cold spell forecast, insulate the plant with something, whether that’s a burlap sack, an old bed sheet, or a bath towel rested on top of wooden stakes… it needs cold protection.
Frost bite will cause yellowing when it’s just below freezing for one to two nights. If the cold damage is sustained for longer, the frost bite turns the leaves brown killing them.
Yellowing and brown leaves should be pruned from the plant when the threat of cold is gone.