Whether you grow potatoes in the ground, in a bag, or a container, your crop can be affected by these issues in any of these scenarios.
1. Blight (early or late) — Early blight shows dark rings, brown spots, or lesions that spread through the plant. It can prevent tubers from reaching full size, and potatoes have dark and sunken lesions. The fungus spreads in hot and dry weather where the leaves of potato plants are wet from watering. Remove any leaves or stems affected. Avoid early blight by watering crops from the bottom, and avoid splashing water on the leaves when watering. Late blight attacks potatoes’ foliage and tubers in the summer and is common during warm, wet, and humid weather.
When the weather has two consecutive days over 50F, and with 6-10 hours of 90% humidity, that is the prime time for the spores to develop and spread quickly. Blight symptoms include brownish-black spots or blotches appearing on leaves and stem, starting on the tips of the leaves and causing them to collapse and wither. The disease, if unchecked, will travel down the plant and infect the tubers, causing a red-brown decay and then rotting.
If you spot signs of blight, it is best to cut down all affected plants and destroy the foliage. Please do not add them to your home compost, as it can spread the spores around the garden in the soil next year. Leave the tubers in the ground for a few weeks and then dig them up to use, but make sure not to store potatoes from affected plants.
You can buy fungicidal treatments engineered specifically for blight management – both early and late blight – such as Bonide Copper Fungicide, which we carry here at Wilson’s (keep in mind this product is harmful to
2. Small Tubers — Potatoes love fertile soil and a sunny spot. The plants want to capture that sunlight and absorb all the nutrients it needs to grow in size and develop tubers. An absence of some nutrients, or an excessive quantity of any, can cause problems and a smaller harvest. The plant needs a balanced mix of nutrients from well-rotted manure, compost, or fertilizers.
Most chemical fertilizers you buy for potatoes are relatively balanced in nitrogen, phosphorus, and potassium – usually equal amounts of the first two and around half of the potash. Check the plant fertilizer number on the label for the exact breakdown. However, getting that balance wrong in your soil can have devastating effects. For example, just applying manure will put far too much nitrogen in the soil, hitting the development of tubers, delaying the setting of skin on the potatoes, and leaving the plant more vulnerable to disease.
In addition to healthy moisture balance, potatoes require well-balanced fertilization. Nitrogen promotes lush foliage, but we’re seeking root development in potato farming. An overabundance of nitrogen can cause plants to put all their energy into leaf development rather than bulking their tubers. Seek moderately balanced nitrogen, potassium, and phosphorous ratio for optimal growth.
3. Yellow Leaves —Potatoes like moisture in the soil to grow; however, it is very easy to overwater them, leading to significant potato growing problems. When any plant is overwatered, the spaces in the soil that generally hold oxygen get filled with water instead. Eventually, roots will suffocate and die. Signs of overwatering include yellow leaves and dieback – which can be challenging to recover from.
Potatoes need 1-2 inches of water weekly from rainfall and irrigation. Take care not to over-saturate the ground, and use your finger to check the moisture levels around 6 inches deep. If you use irrigation, then ensure to take any rainfall into account. Other potential methods to prevent overwatering include planting the tubers in raised beds or digging drainage trenches between the rows.
4. Frost Damage — Potato plants can be susceptible to damage from Frost either due to planting the crop too early or the climate throwing up unexpected late frosts. Damage happens when temperatures drop below 30˚F. The signs of frost damage are leaf margins going black or the foliage dying. Avoid planting your potatoes too early, holding off until the soil is consistently above 40˚F before planting your crop.
Melvin Cubian, the gardening expert from PlantIn, warns of the dangers frost poses for potato plants and recommends what to do if any late frosts are predicted in your area. He says: ‘Frost injures the plant as the water molecules freeze, forming sharp ice crystals piercing through cell walls. As a result, fragile leaves (mainly the top shoots) and the young tubers would show water-soaked lesions and wilt.
‘After hearing a frost advisory, waste no time earthing up the exposed tubers and putting grass straw mulches to insulate them from the cold.’
If you are growing your potatoes in a bucket, container, or bag, then you should move the plants to a more sheltered spot if there is a forecast for late frosts in your area.
5. Green Potatoes — One of the main tasks throughout the potato growing season is to hill up plants as they grow. When the potato foliage grows around 8 inches above the ground, hilling up involves mounding more soil or organic matter around the plants – until only the tips appear. Hilling up is done repeatedly throughout the growing season as it helps to increase the yield. Tubers must remain covered and in darkness as they grow. If potatoes break through the soil surface and are subjected to light, it can cause the development of chlorophyll – which can cause problems if consumed. Throw away any green potatoes that show signs of glycoalkaloid production. This task may be harder to accomplish in a pot—keep the soil covering the potatoes until it reaches the top of the container.
6. Hollow Centers — Known as hollow heart disease, although not an actual disease, it causes a cavity to form in the center of the potato tuber. Rapid changes in the growth rate of a tuber may cause this deformity.
Growers need to ensure no extended periods of overwatering or underwatering that can stress the tubers. If there are periods of extreme heat predicted, then consider mulching potatoes to keep them cool to avoid succumbing to hollow heart disease. If you are growing potatoes in a bag or container, move them to a sheltered spot in periods of such heat.
7. Pests — While containers may reduce some garden pests, they won’t protect your potatoes from every potential invader. That’s why you must check your plants occasionally for any signs of problems.
Wilted plants, yellowing or discolored leaves, leaf holes, leaf stippling, and other issues may all be signs of pest activity. Or you may spot the pests themselves wreaking havoc on your plants. Insects like Colorado potato beetles, aphids, and cutworms are common potato pests and may crop up in your container garden.
Handpicking pests is one way to keep your plants safe, but you may also want to try out companion planting, which can naturally keep pests away. Sowing onions, leeks, chives, coriander, tansy, or sweet alyssum near your potato plants can repel pests or attract beneficial insects that will feed on pests and keep your plants protected.