Sweet Potato Leaves Turning Purple

If you’ve noticed your sweet potato leaves turning purple, it’s natural to be concerned. This unexpected color change can signal several things, from a simple natural process to a cry for help from your plant.

Let’s look at the main reasons behind this purple hue. The color comes from pigments called anthocyanins. These are the same pigments that make blueberries blue and red cabbage red. In sweet potato leaves, they can appear for both good and not-so-good reasons.

Common and Harmless Causes

Often, the purple color is completely normal. It’s part of the plant’s character.

Varietal Trait: Many sweet potato varieties naturally have purple-tinged or even fully purple leaves. ‘Blackie’ or ‘Marguerite’ are examples. Check if the purple is consistent and the plant looks otherwise healthy.
Sun Exposure: Just like we tan, plants can change color with sun. Intense sunlight can trigger anthocyanin production as a natural sunscreen. Leaves facing the sun might turn purple while shaded ones stay green.
Cool Temperatures: Chilly nights, especially in spring or fall, can prompt a purple flush. It’s a temporary stress response that usually fades as temperatures warm.

Nutritional Deficiencies Causing Purple Leaves

When the purple is combined with stunted growth or odd leaf shapes, it’s often a nutrient issue. The plant isn’t getting what it needs from the soil.

Phosphorus (P) Deficiency: This is the most common nutritional cause. Phosphorus is vital for energy transfer. Without it, older leaves can turn a dull, dark purple or even bronze, starting at the edges and moving in.
Potassium (K) Deficiency: While less common, a lack of potassium can cause purple spots or patches on the undersides of leaves, along with yellowing edges.

How to Fix Nutrient Problems

Don’t just add fertilizer blindly. First, try to confirm the issue.

Get a Soil Test: This is the best step. It tells you exactly what your soil lacks. Your local extension office can help with this.
Adjust Soil pH: Sweet potatoes prefer slightly acidic soil (pH 5.8-6.2). If your soil is too acidic or too alkaline, nutrients get “locked up” and plants can’t absorb them, even if they’re present.
Use the Right Fertilizer: For a suspected phosphorus deficiency, use a balanced, slow-release organic fertilizer or add bone meal. Avoid high-nitrogen fertilizers, which boost leaves at the expense of tubers.

Environmental Stress Factors

Sometimes, the environment itself is the problem. These stresses can trigger that purple pigment.

Water Stress: Both too much and too little water can cause problems. Overwatering leads to soggy roots that can’t take up nutrients, mimicking deficiency. Underwatering puts the plant in general survival mode.
Root Bound Plants: If your sweet potato is in a container, check the roots. Circling, dense roots can’t access enough water or nutrients, leading to stress and purple leaves.

Step-by-Step: Diagnosing Your Plant

Follow these steps to figure out what’s going on in your garden.

Observe the Pattern: Is the purple on new leaves or old leaves? Is it on the top side or underside? Is the whole plant affected or just sun-facing leaves? Take notes.
Check the Stems and Veins: Sometimes, stems turn purple first. Also, see if the leaf veins are purple or if the color is between the veins.
Review Your Care: Think about recent weather. Have their been cold snaps? Has it been unusually sunny? How have you been watering?
Inspect the Roots (Carefully): Gently check the soil moisture and, if possible, look at a few roots. They should be firm and white or tan, not mushy and brown.
Compare to Variety Description: Look up the specific variety your growing. Does it mention purple foliage?

Action Plan and Solutions

Once you have a likely diagnosis, here’s how to respond.

If It’s Natural (Variety or Sun):

No action needed! Enjoy the beautiful foliage. The tubers will develop normally.

If It’s a Deficiency:

Amend soil based on a soil test recommendation.
Apply a side-dressing of compost or balanced fertilizer.
For a quick phosphorus boost, you can use a liquid fertilizer like fish emulsion, following label instructions.

If It’s Water Stress:

For Overwatering: Let the soil dry out more between waterings. Ensure your container or garden bed has excellent drainage. Consider raising your garden beds if soil is heavy clay.
For Underwatering: Water deeply and consistently. Sweet potatoes need about 1 inch of water per week. Mulch heavily with straw to retain soil moisture.

If the Plant is Root Bound:

If it’s early in the season, you can carefully transplant it to a larger container or a garden space. If it’s late, just maintain consistent care and harvest will be smaller.

Prevention for Future Seasons

The best medicine is always prevention. Keep your sweet potatoes happy from the start.

Prepare Soil Early: Mix in several inches of compost or well-rotted manure before planting. This improves drainage and provides slow-release nutrients.
Test Soil pH: Do this a few weeks before planting so you have time to adjust it. Garden lime raises pH; sulfur lowers it.
Choose the Right Location: Plant in full sun, but if you live in a very hot climate, some afternoon shade can prevent sun-scorch stress.
Water Wisely: Use a soaker hose or drip irrigation to water the soil, not the leaves. This prevents disease and ensures deep watering.

Frequently Asked Questions

Q: Are purple sweet potato leaves safe to eat?
A: Yes, they are! They are nutritious and can be cooked just like spinach or kale. The purple color might even add antioxidants to your diet.

Q: Can sweet potato leaves be purple and still produce good tubers?
A: Absolutely. If the purple is from variety or mild sun stress, tuber production is not effected. If it’s from a severe, uncorrected deficiency, yield may be lower.

Q: My plant’s leaves are purple and also curling. What does that mean?
A: Curling plus purple often points to a more severe phosphorus deficiency or possibly an issue with water uptake from damaged roots. Check soil moisture and drainage immediately.

Q: Should I remove the purple leaves?
A: Generally, no. They are still helping the plant. Only remove them if they are truly dead and crispy. Otherwise, diagnose and treat the underlying cause.

Q: Is it too late to fix purple leaves?
A> It’s rarely too late to help the plant. While severely damaged leaves may not turn green again, new growth will come in healthy once you correct the problem. The key is to act as soon as you notice the issue.

Seeing your sweet potato leaves turning purple can be a suprise, but now you know it’s a solvable puzzle. Start by checking the easy things—variety and weather—before moving to soil and nutrients. Most often, with a simple adjustment to water or fertilizer, your plants will bounce back and you’ll be on your way to a great harvest of tasty tubers and greens.