Home gardeners are sometimes shocked to see something quite unusual on their potato plants: fruit! While we may often notice small blossoms in July or August, few people have seen the fruit that look like green cherry tomatoes at the top of the plants.So, should we remove potato fruit from our plants?
Well, if you believe the theory that a potato plant will produce larger and more abundant tubers if you keep it from flowering and fruiting, then yes. But is there any truth to that theory, or is it just a myth? What if we allowed our potatoes to fruit?
What is potato fruit?
Potatoes belong to a small family of plants – the Nightshade or Solanaceous family – along with eggplants, peppers, tobacco, and tomatoes. Not surprisingly, as tomatoes and potatoes are both members of the same genus, they both produce berries.
After flowering, some potato plants produce green fruits about the same size as cherry tomatoes, each containing hundreds of tiny seeds. But while we eat the “fruit” of tomato plants, the berries of potatoes are poisonous, so they’re not edible.
Toxic
They contain high amounts of solanine so you can become very ill if you eat them. Solanine is a toxin that can also be found in potatoes that have been dug up and left in the sun so that the skin turns green.
Besides tasting very bitter and unpleasant, if you eat plant parts that contain solanine, you may experience abdominal pain, diarrhea, or headache. If young children are around, it may be best to remove potato fruit so that your kids are not tempted to eat them.
How toxic are potato fruit?
Potatoes, like all nightshade plants, form toxic substances called glycoalkaloids. They are produced in only small amounts in the tubers, but typically much higher amounts in the foliage and the berries.
In fact, in many commercial varieties of potato, the berries usually have about 10 times the level of glycoalkaloids as the tubers. Potato tubers are considered safe to eat when they contain less than 200 milligrams of glycoalkaloids per kilogram of tubers. Berries may contain as little as 177 mg/kg of glycoalkaloids or as much as 1350 mg/kg or more.
So, just how dangerous is that?
Symptoms
Well, some people begin to experience symptoms of toxicity at about 1 mg per kg of their body weight. So, a person who weighs about 130 lbs could consume somewhere between 1 ½ to 10 ½ ounces of potato berries without developing symptoms, depending on the level of glycoalkaloids in that particular berry.
This means that an adult who eats a few potato berries might not have any symptoms – or at worst, might spend a few hours vomiting and/or with diarrhea.
Of course, the solanine levels in potato berries are much less tested than those of the actual tubers, so you should definitely contact your doctor if you have eaten potato berries. And the situation would be more serious for children, since with their lower body weights, it would be easy for them to “overdose” on potato fruit.
Make sure that they understand that the berries are not edible.
What does potato fruit look like?
While both potato and tomato plants produce flowers and fruit, tomatoes have small flowers and large berries, but potato flowers are large and their berries are small.
Potato fruit are also known as seed balls, potato apples, potato tomatoes, or simply “berries”, which is – botanically speaking – the most accurate description.
They actually resemble small cherry tomatoes, but the skin often does not colour and remains leathery. They can be round or oblong and are typically green, but some can be red or purple. Others are a deep blue, and turn almost black as they ripen.
Potato berries most often grow in small clusters, hanging from one large stem, though some have individual stems. Inside, each berry contains up to about three hundred true potato seeds, although many varieties produce much smaller amounts.
Why does potato fruit form?
Since it’s so unusual to see potato fruit, it must be rather difficult for them to be formed, right? Not necessarily – under the right conditions, many potato plants can bear fruit. There are several factors that are important to berry production:
Climate
Potatoes are native to cool, temperate areas in South America – like the Andes mountain range or near the coast of Chile. Both areas share a cool and often humid climate.
Because potatoes tend to flower and form berries best under their native conditions, if the temperature stays under 80 degrees with high humidity, the plants will fruit much more abundantly.
Disease
Over time, potatoes can accumulate a host of different diseases, particularly viruses. While those viruses decrease the yield of the plant, they also often decrease the ability of the plant to flower and produce fruit.
You are more likely to see flowering on fresh, certified seed potatoes than if you are using tubers saved over multiple years. Certified seed tubers usually have a lower disease burden, leading to a higher rate of flowering.
Genetics
Humans typically choose potato varieties known for heavy yields of large tubers. Over thousands of years of selective breeding, we probably didn’t care much about berries, since we don’t eat them or use them to propagate the plants in most cases.
As a consequence, many varieties of domesticated potatoes rarely or never flower – even in ideal conditions. Some may flower but fail to hold their berries. Only a small percentage of modern potato varieties are reliable flowerers. But wild potatoes often produce a much greater yield of berries than tubers.
Pollination
Potatoes are most effectively pollinated by bumblebees, who vibrate their wings very quickly to dislodge pollen from the flower. Other pollinators don’t do this, so honey bees (for example) are poor potato plant pollinators. If you have noticed a lot of bumblebee activity in your potato patch, it could explain the development of potato berries.
Sterility
Many modern potato varieties have sterile pollen. This means that the “male sterile” varieties will not produce berries unless there is another fertile variety nearby that can pollinate them.
If you’re growing multiple varieties of potato in the same garden, you may notice more berries as your plants have likely cross-pollinated. If you’re growing your potatoes from seed, you could be more likely to see berries on your plants, as they may not all produce sterile varieties.
How does potato fruit form?
Whenever spring and summer weather has been unseasonably cool, potato plants are more likely to produce berries. While we typically use seed potatoes – cut up portions of the tubers – to propagate our crops, potatoes can also reproduce sexually without or without our help.
Potato flowers and fruit are produced because this is how the plants naturally multiply themselves: by seed.
As with most plants, potato plants bloom. Potato flowers look very much like tomato flowers except instead of being yellow, the potato flowers can be white or lavender or pink. In most years, July and early August are hot and dry months, so usually the flowers will dry up and fall from the plant without setting fruit.
Cooler weather during long summer days, and a decent amount of rain or humidity will allow the flowers to remain, pollinate and grow into small potato fruit.
But most of the time, the flowers on a potato plant are not fertilized, and the plant does not produce any fruit. Since commercial potatoes are usually grown from cut-up seed potatoes, the lack of fruit isn’t usually an issue.
Should I remove potato fruit?
Probably not – unless you’d like to try growing potatoes from the seed. Removing potato fruit isn’t a common practice, but if you have young children and you are worried that they might eat the berries, go ahead and remove them.
Some gardeners believe that berry production can reduce the crop yield of your tubers. In some plants, diverting resources into sexual reproduction can decrease the yield, but as both tuber and berry production both begin after flowering, there is no competition for the potato plant’s energy at that point.
Most large-scale potato farmers don’t prune the fruit from their potato crops, even with varieties that fruit heavily, since the cost of the work involved would exceed the value of the difference in yield.
In fact, we’re still not sure to what extent fruiting affects potato yield – and most varieties produce so few berries that you wouldn’t see much difference anyway.
When are the berries ready to harvest?
The easiest way to harvest the berries and extract the seeds is to wait until the berries ripen and fall of the plant and then collect them off the ground. If you find that pests are eating the fallen berries, you may want to pick them after they have hung on the plant for six weeks, when they are still fairly hard and unappealing to animals.
You could also cover the young berries with a mesh bag to protect them and keep them from getting lost.
Any berry with at least a ½-inch diameter probably contains viable seeds, but the seeds will become larger and produce better seedlings if they’re left to mature as long as possible.
Once picked, you should let the berries ripen until they are soft to the touch before extracting the seeds.
Can you grow potatoes from seeds?
Because potatoes are typically grown from seed tubers, you may not have ever thought about the actual seeds of the potato plant.
In fact, it can be a little difficult to find information about potato berries and seeds given that we call the tubers that we plant “seed potatoes.” But when you grow a plant from a tuber, it is actually a clone of the same original plant.
But if you’ve had problems with potatoes diseases, are tired of paying more for tubers that have been certified disease-free, or just like to experiment with your crops, you may want to try growing your next crop of potatoes from true seed.
You see, all new potato varieties are grown from seeds, which may also be called “true potato seeds”, “TPS” or “botanical seeds” to distinguish them from seed tubers.
Cloning
So, while every tuber grown from a seed potato is a clone of the same plant, every seedling grown from TPS is genetically unique and will produce tubers with different characteristics than the parent.
In most cases, the genetics of potato seeds are not predictable, and may produce undesirable traits.
In fact, after so many years of cross-breeding and cross-pollination, each of the hundreds of seeds inside a potato berry could grow into an entirely different variety.
While tubers are the only predictable way to grow the same variety from a parent plant, researchers can use seed pods to develop brand new varieties with new flavors, colors, and characteristics. But it may take several years of cultivation until that new variety is bred thoroughly enough to be grown predictably from tubers.
How do you remove and store the seeds for planting?
The simplest way to harvest potato seeds is to wait until the berries are fully ripe and very soft and just squeeze the seeds out. Or if you want very clean seeds that are suitable for long term storage, you can extract them with a blender and treat them with detergent to break down any substances that could prevent germination.
The easiest way to separate the seeds is to mash the ripe berries and put the resulting mix into a glass of water. Let it sit for 3-4 days to allow the mix to ferment and then strain out the top debris. Any viable seeds will have sunk to the bottom of the glass.
You should rinse them well and allow them to air dry on a paper towel before placing them into a paper bag, and storing them in a cool dry place until you’re ready to plant. Remember that plants started from seed take longer to develop than those started from tubers.
So, should you remove your potato fruit?
As a general rule, you don’t need to remove potato fruit – unless you’re worried that someone may inadvertently eat enough to poison themselves. Or you plan on harvesting the seeds and trying your hand at growing some interesting varieties of tuber. How much fun would that be?
