Potato plants (Solanum tuberosum) produce leafy tops that grow to 40 inches tall, explains the International Potato Center. The tops perform photosynthesis and manufacture energy that is stored as starch in the underground tubers. Without the tops, your potato plants cannot perform photosynthesis, and tubers will not grow. However, there are times when the tops may need to be selectively cut back. Let’s find out – can you cut the tops off potato plants?
Can you cut the tops off potato plants?
Under normal growing conditions, potato tops do not need to be cut back as they will inhibit the growth of the underground tubers. However, there are some times when cutting back your potato plants may be beneficial. The main reasons are to control growth, remove disease/pests, or make harvesting easier.
Why would you cut the tops off before the potatoes are ripe?
The main function of removing or cutting the tops off your potato plants is to stop your potato tubers (the potatoes) from growing too large. This is only usually necessary when the potatoes under the soil have grown large enough but there is plenty of growing season remaining.
Although pruning or cutting back your potato plants to control growth and keep them from becoming overgrown is not generally recommended or practiced, you can selectively prune a few top leaves to help keep them under control. This is usually done if the potato tops are crowding other plants which were planted too close.
Keep in mind that if you remove too much of the tops, your plants will not be able to perform photosynthesis and manufacture the energy needed to form large, healthy tubers.
As an alternative, pinching out the new growth at the ends of the stems will prevent the potato plant from growing taller and force new growth along the stems. This will cause the plants to become less tall, bushier, and more compact and may make them easier to care for and reduce the chance of them blowing over.
To Control Disease
Potato plants infected with diseases like potato blight may benefit from trimming away the diseased leaves to prevent the disease from spreading to nearby plants.
Gardener’s World recommends cutting the potato foliage to the ground if they become infected with Blight. This will stop the potatoes from growing, but it may allow you to save your potato crop. Cutting the tops off the potatoes may prevent Blight from traveling down the stem and infecting the tubers.
To Remove Insect Pests
Insect pests, like the Colorado Potato Beetle, often lay their eggs on the undersides of potato plant leaves. These eggs can be difficult to remove by hand and often survive pesticide applications. Cutting off leaves with insect eggs can be an effective part of insect control. Likewise, leaves with masses of newly hatched bugs can be cut from the plant and destroyed.
Removing a few leaves from your potato plants won’t affect the plant’s health and won’t stop tubers from forming under the soil.
To Make Harvesting Easier
Many gardeners prefer to cut the potato foliage back to the soil level before harvesting their potatoes. This causes the potato tubers to stop growing and the skins to begin to toughen. If you choose this method, wait a week or two after cutting the foliage off the potatoes before harvesting and curing them.
Remember that potato foliage dies back naturally in the fall when the tubers mature. Unless there is a reason for hurrying the process, such as you are moving to a new home or going on an extended vacation and need to harvest them early, there is no reason to cut the tops back prematurely.
Care should be taken when removing potato tops – you should cut them off rather than pulling them, as pulling the tops increases the chance of pulling the potatoes from the ground. This is especially true if the potato tops have not ripened and naturally begun to detach from the potatoes. If you are using a mechanical flail or topper machine keep it raised up from the soil 12″ and keep your forward speed slow to keep damage and pulled potatoes to a minimum.
How should I dispose of my unwanted potato tops?
Healthy potato tops can be put in the compost bin but beware of composting potato foliage that is infected with disease such as potato blight or tops that harbor insect pests.
According to Gardener’s World, potato tops infected with Blight should not be composted or disposed of near the garden. If possible, destroy the tops by burning them. Otherwise, place them in a trash bag and secure the top tightly before sending them to the transfer station or skip yard.
Likewise, potato tops that harbor insects, like the Colorado Potato Beetle, should be destroyed by burning or disposed of away from your gardening area.
Many diseases and some insects will survive composting and may contaminate all of your compost, especially if the compost is not mature by the end of the season.
Will my potatoes grow back if I cut off the tops?
Some plants (namely, perennial or annual flowers and green leafy veggies like lettuce, spinach, and chard) can be cut to the ground when they become overgrown and will happily send up a new flush of growth. Potatoes aren’t one of those plants. If you cut all the foliage off your potato plants, the plant will die, and the underground tubers will stop growing.
What should I do if my potato plants are too tall?
The most common reason potato plants produce massive tops is overfertilization, especially with a formula high in nitrogen. If you suspect this is why your potato foliage is overgrown, stop fertilizing them for the rest of the season. This will help control the growth of the potato tops and keep them from growing too tall.
For potatoes that are already overgrown with huge tops, there are two ways to try to keep them under control.
Hill the Potatoes
Hill the potatoes by mounding extra soil around the base of the plant. This serves two purposes. It gives the tubers the room they need to grow and prevents them from becoming exposed to the sun and turning green. It also provides support for the growing potato tops.
Don’t worry if hilling covers some of the lower leaves on the plant. The stem will form new roots and anchor the plant more strongly to the soil.
Stake your potatoes.
If you are growing your potatoes in containers, add a stake to the container and tie the foliage to it with plant ties or strips of soft cloth, such as cotton ribbon or a cut-up t-shirt.
For potatoes grown in rows in the garden, erect stakes every two to three feet along both sides of the row. String garden twine or rope along both sides of the potato plants to provide support for the growing vines. For best results, string the twine at several heights, such as every 6 to 8 inches, to corral the potato plants and keep them upright.
Potatoes are heavy feeders and need adequate fertilizer and plenty of water to thrive. However, you must use caution with applying fertilizers with too much nitrogen. For best results, apply 5-10-10 fertilizers when planting your potatoes in the spring to prevent issues with massive tops and few tubers.
In a normal growing season it is not necessary to cut the tops from your potatoes – however, removing potato plant tops is beneficial if your potatoes are large with plenty of growing season remaining, the tops are infected with disease or pests, or if the potatoes have fully ripened naturally the dead fops/foliage can be removed to make harvesting easier. Good luck!