Potato Plants Turning Yellow: why?

If you’re new to growing potatoes, at some point you’ll ask yourself, “Why are my potato plants turning yellow?”. Most likely, this is a natural part of the lifecycle, and means the plants are mature.

But sometimes it can be a sign of disease, nutrient deficiency, or over-watering

Potatoes are an amazing crop to grow. They are relatively easy to grow, store well, are an excellent source of calories, and can be cooked a million ways. Growing your own potatoes can be a new gardening challenge, a step towards becoming more self-reliant, or a great way to grow uncommon potato varieties. 

Potato plants turning yellow

Regardless of why you’re growing potatoes, it’s good to brush up on some background knowledge. Especially to know whether your yellowing potato leaves are a sign they’re mature or a sign that something wrong. 

More often than not, yellow leaves mean your potato plants are ready to harvest. Should there be something wrong, however, it’s important to know when to intervene. This overview will give you all the information you need to know whether your yellow potato leaves are a positive or negative sign.

Disease in potato plants

If your potato plants are turning yellow before they are mature, it can be a sign of disease. Wilt and blight are the most common diseases facing potato plants.

If you’ve ever grown tomatoes (another plant in the Solanaceae family), you might be familiar with wilt and blight. Both of these diseases can be challenging to address in a home garden and early action is key. 

Fusarium wilt and verticillium wilt are two soil-borne diseases that affect potato plants. Older leaves hanging close to the ground will yellow first followed by the rest of the plant. 

Potato Blight

Potato blight is another common disease potato plants are vulnerable to. Blight causes browning of the leaves with dark spots. 

Potato plant showing black circles of potato blight on the leaves
Image above showing the first stages of potato blight on the leaves as black circles. This then kills the entire leaf and moves through the infected plant and entire crop in days if unchecked.

Should you suspect wilt or blight to be the problem, it’s important not to contaminate other parts of your garden. They can stay alive over the winter in the soil or in stored tubers. 

Prevent the disease from affecting your plants next year by: 

  • Do not use potatoes from this harvest as seed potatoes for the future.
  • Don’t toss the leaves in the compost. 
  • Never plant potatoes (or tomatoes) in the same spot for at least 3 years. 
  • Choose specific varieties that are disease resistant. 

Treating potato blight can be difficult for home gardeners. Many good chemical blight sprays require licences to use.

There are some products available without a commercial grower license such as Bonide Copper Fungicide. This can help prevent and delay the spread of potato blight in your crop.

 

Mineral Deficiency

Yellow leaves in potato plants can indicate a lack of vital minerals. Magnesium and nitrogen are essential minerals for healthy plant growth. The magnesium is used by the plant in the production of chlorophyll and nitrogen is essential for plant growth.   

dying potato plant leaves due to excess spray
Suspected magnesium deficiency or over application of some sprays

Often magnesium deficiency causes yellowing leaves in potato plants because it cannot produce chlorophyll (what makes plants green). 

Lack of nitrogen can also cause the leaves to lose their colour because the plant isn’t able to grow. Without nitrogen, plants can’t make new cells and are effectively stunted.  

Cal-Mag Plus is a Magnesium plant supplement additive that can be added to water for plants showing deficiency.

Yellow leaves

Correct yellow potato leaves due to nutrient deficiency by amending the soil or applying fertilizer. To introduce nitrogen, apply composted manure or a nitrogen-rich fertilizer. To correct for a magnesium deficiency, apply rich compost or through a foliar spray for quick-results. 

When introducing amendments into the soil take into account that they may take time to be accessible by the plants. Some slow solutions, such as compost, will take months until all the nutrients are soluble. 

If you aren’t able to correct the mineral deficiency issues in time, don’t despair. You’ve gotten to know your soil a little better and can prepare for the future.  

Waterlogged soil

Too much water in the soil can cause your potato plants to turn yellow. Whether it be from excess rainfall or overwatering, over wet soils are a breeding ground for trouble.

Waterlogged potato plant showing yellow and dying leaves
Waterlogging can cause stress on the plant leading to leaves yellowing and dying.

Overwatered plants will develop root rot and are a lot more susceptible to diseases such as wilt and blight. Excess water will leach out nutrients and waterlogged soils make it difficult for roots to access oxygen. 

If you know your area gets a lot of rain, choose potato varieties with higher disease resistance. In small areas, you can modify your soil to make it drain better or consider growing potatoes in large containers with good drainage. 

Potato plants turning yellow

When potatoes mature their leaves naturally begin to change colour. Potato plants turning yellow indicate that it is almost time to harvest. They signal to the grower that the plants are redirecting their energy from growing lush foliage to maturing the potatoes. 

When you’re potato leaves turn yellow late in the growing season, it’s a safe bet they’re ready to harvest. Pull the first plant out of the ground, check the tubers, and if you’re happy harvest and store the rest. 

Potato plants ripening

When potato plants are mature and ripe for harvesting, they will show this through yellow leaves. Yellow leaves are a welcome sight when they indicate that it’s time to pull your potato crop out of the ground. 

Sometimes potato plants can begin to yellow early if there are temperature fluctuations that force them towards yellow maturity. Monitoring the weather will help you determine if this could be a cause. Warm temperatures early in the season, for example, can sometimes force the plants into early maturity. 

Should this happen, it’s not a big deal. Simply harvest your potatoes and take advantage of the space to seed a quick-growing crop in that space. 

Conclusion

There are many probable causes for why your potato leaves are turning yellow. Most likely, the change in colour means they are maturing and almost ready to be harvested. As the potato plant finishes its life cycle, it puts more energy into growing the tubers than maintaining the leaves.

There are a few other issues such as nutrient deficiency and waterlogging that can also cause potato leaves to turn yellow. Understanding the possible causes of yellowing potato leaves will help you determine whether they are a natural occurrence or a symptom of something gone wrong. 

Understanding why your potato leaves are yellow will help you know how to respond. Is it time to harvest? Do they need less watering? Or does the soil need to be fertilized?

a healthy field of potatoes with one plant with yellow leaves
A healthy field of potatoes with one plant with yellow leaves – nothing major to worry about.

There are many courses of action to address yellowing potato leaves. Use the information in this article to monitor possible causes. When you understand the cause, you can respond efficiently and potentially save your potato crop harvest.