A good average for how tall a potato plant will grow is 24-36 inches. If you’re potato plant is tall and spindly it may not be getting enough sunlight. If a potato plant is excessively tall and bushy, too much nitrogen could be the cause.
Gurney’s Seed & Nursery Co. lists both the average height and width of the different varieties of seed potatoes they sell. The large majority of them are listed at 24-36 inches tall. If you know the variety of potato you want to plant you should be able to find a better idea of how tall they should be.
Do Potato Plants Need Support
Potato plants naturally grow bushy and for the most part should not need support. They have no fruits hanging from their branches that need support. In potato fields the plants grow 2’x2′ and stand up on their own.
If you think support will help a potato plants foliage to get more sunshine and don’t mind the extra task it won’t do any harm and might do some good.
Can You Cut Back Potato Plants?
Yes you can cut back potato plants but there’s not many good reasons for doing so. You do not need to cut back any foliage when hilling and if you choose to cut back potato plant foliage to reduce shade casted it’s likely you will reduce your potato crop yield somewhat.
If you have frost damage in the early spring trim the plant back to about an inch above the soil and it should recover and grow back fine when the weather warms up.
Pinching potato flowers off to give better yields is questionable. The point is to stop the plants energy from going to flowering and producing seed but it might just stress the plant out more then it helps redirect energy towards tubers.
The most common cutting back of potato plants is done two weeks before harvest. You cut the plants off at their stem 2-3 inches above the soil to kill the plant off completely. This tells the tubers it’s time to harden up and their skin becomes thicker and the potatoes store better for a longer time.
Potato Plant Too Tall & Bushy
Potato plants with excessive vegetative growth happen when the plants are given a nitrogen heavy fertilizer at the tuber bulking stage, about the time of flowering. In this case there is too much foliage growth above ground and not enough tuber growth below. If a potato plant is under fertilized it will start to turn yellow long before it’s time for this and new growth will be emerging yellow.
Potato Plants Falling Over
There are a number of reasons why potato plants could be falling over including the plants reaching the end of their life cycle, a bad storm with high winds, poor soil nutrient levels, over or under watering, a harsh season (temperature or rainfall), or pests and disease.
With a little common sense and observation we can get to the cause of the potato plants falling over. Depending on the cause there will be zero cause for concern, or something that could cause a lower yield come harvest time, or potato plants could be at the end of their life cycle.
Sun vs Shade – During hot spells with temperatures over 85 degrees it’s a good idea to shade the plants during the hottest hours of the day. Shade cloths are designed for this but you can use bed sheets, outside umbrellas, or anything you can think of.
Plants Reaching Maturity – If you’re plants are reaching maturity it is normal for them to start to die off. The plants will start to turn yellow and brown and lie down. This is completely normal and not a problem at all.
Keep dates written down so you will know when you planted and how long the variety you’re growing takes to reach maturity. Another way to know it’s this time for your potato plants to die off is around 6 weeks after they have flowered.
When you have two weeks left before you plan to harvest stop watering completely and cut the plants down leaving only a couple inches above ground to know where the potatoes are. This will send a signal to the tubers that the plant is completely done growing and the potatoes skin will toughen up and they will store better.
The Season – If you planted your potatoes late or get hit with an extra hot early season you may face problems. Potatoes are cool weather plants and grow best in moderate climates. If you’re facing highs above 85 and lows above 70 consistently you could see heat exhaustion above ground with wilted leaves and yellowing and little tuber production below ground.
This is why it’s so important to get your potatoes in the ground as soon as possible in the spring when the weather is perfect for potatoes. Less likely is having excessive rain with your soil not draining well leaving your potato plants in a constant puddle. If this happens you could face root rot and the plants dying off completely.
Soil Nutrient Levels – If your soil is low in nutrients you may see stunted growth, yellowing of plants too early in the season, and new growth emerging yellow.
Gardeners can create a problem by feeding plants with fertilizers high in nitrogen at a time when the tubers should start bulking. At this stage to encourage tuber growth and not foliage growth try and use fertilizers with an N-P-K ratio of 1:2:2.
Watering – You want even and deep watering aiming for 1 to 2 inches of water a week. Water with 1″ a week during the vegetative stage and 2″ a week during flowering and hot weather. Cut back to 1″ of water a week when the flowers disappear and the plants start to die off and stop irrigating completely two weeks before harvest. Watering before or after a mild to moderate rainfall to get a deeper watering.
A rain gauge will give you an accurate rainfall in you garden and if you use sprinklers how much water they give off in certain time frames.
Pests – The most common pest to your potatoes is the Colorado potato beetle. These will not cause your plants to fall over but can completely defoliate them. If you find your potato plant completely severed at the base and lying flat on the ground the culprit is most likely cutworms. Cutworms are also a common nuisance and most easily neutralized with collars around the base of your plants.
Disease – A common disease that can affect your potato plants is blight. Blight comes in two varieties, early and late, and can affect plants in the Solanaceae family including potatoes, tomatoes, peppers, and eggplants. Both varieties spread rapidly in damp weather with outbreaks commonly taking place after extended rainy periods.
Early blight will show up first on older leaves towards the bottom of the plant as brown spots surrounded by yellow coloring. Late blight is responsible for the Irish Potato Famine of 1840 and will show up on the plant as dark water mark like spots on the leaves towards the bottom of the plant and the tips of the leaves.
Please comment below with your own experiences or thoughts about how tall potato plants get.