Growing potatoes from seeds

Q. Do root vegetables like sweet potatoes count as vegetables or starches, and is it true that all the nutrition is in the skins?

A. Potatoes have fallen from grace in recent years, as health authorities have argued that starch-filled spuds shouldn’t be counted as a vegetable in the diet. The USDA recently proposed reducing the amount of potatoes served in school lunchrooms. But the attack on potatoes leaves some confusion: Should sweet potatoes and other tubers and roots also be lumped into this category?

Linda Antinoro, a registered dietitian at Brigham and Women’s Hospital, says that when evaluating meals, she and her colleagues consider both the potato and sweet potato to be starches. Like white potatoes, sweet potatoes have a high amount of starch — an abundant carbohydrate found in all kinds of plants — compared to other vegetables, which means that a portion of sweet potatoes has about triple the calories of a similar volume of carrots or other vegetable.

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However, Antinoro adds, “we would encourage people to eat a sweet potato rather than other starches.’’ By replacing your white potato, rice, pasta, or bread with a sweet potato, you’re adding a whopping dose of beta-carotene, as well as vitamin C, potassium, and other vitamins and minerals.

If you eat sweet potatoes with their skins, you also get a lot of fiber, which can help keep blood sugar levels from spiking after a meal and may also discourage overeating by contributing a sense of fullness. The American Diabetes Association lists sweet potatoes as one of 10 “superfoods,’’ which carry a high nutrition content without sending blood sugar soaring. While it’s not true that the skin contains most of the vitamins and minerals, it contains a large portion of their fiber. Antinoro says it’s always better to eat fruits and vegetables with edible skins to get the most nutritional advantage from their fiber content.

Other high-starch vegetables similar to sweet potatoes include yams, cassava, pumpkin, and winter squashes (e.g., butternut). Antinoro says that most other root vegetables like carrots, beets, turnips, parsnips, and rutabagas have a lower starch content and caloric density than potatoes and sweet potatoes, and can be counted as vegetables rather than starches in your meals. The overall balance to strive for, she says, is a plate that contains about half vegetables, one-quarter starches, and one-quarter protein-rich foods.

What Is True Potato Seed: Learn About Potato Seed Growing

If you have ever grown potatoes before, you are familiar with the process of planting seed potatoes. The term “seed potato” is actually a misnomer and a bit confusing, when in fact, it is actually a tuber and not a seed that is planted. This confusion leads one to ask, “Do potatoes produce seeds?” and, if so, why isn’t potato seed used for growing purposes?

Do Potatoes Produce Seeds?

Yes indeed, potatoes produce seeds. As with most plants, potato plants bloom, but usually the flowers dry and fall from the plant without setting fruit. You’re more likely to see potato seed growing on plants in regions where temperatures are on the cool side; these cool temps combined with long days promote fruiting in potato plants.

Additionally, some cultivars are more prone to fruiting than others. Yukon Gold potatoes are one example. This potato seed pod or berry is referred to as a “true potato seed.”

What is True Potato Seed?

So, what is true potato seed and why don’t we use it instead of tubers (seed potatoes) to propagate?

Potato plants produce small green fruits (berries) filled with hundreds of seeds and about the size of a cherry tomato and with much the same appearance. Although they resemble tomatoes and are in the same family as tomatoes, the nightshade family, this fruit is not the result of cross-pollination with tomatoes.

The fruit, although similar in appearance to a tomato, should never be eaten. It contains toxic solanine, which can cause headaches, diarrhea, cramps, and in some cases, coma and death.

True Potato Seed Information

While potatoes grown from tubers or seed potatoes produce and exact genetic clone of the mother plant, those grown from true potato seed are not clones and will have different characteristics than the parent plant. True potato seed is most often used by plant breeders to facilitate hybridization and fruit production.

Potatoes grown on commercial farms are hybrids selected for their disease resistance or high yields that can only be passed on through “seed potato.” This assures the grower that the desired qualities of the hybrid are passed down.

It is, however, possible to grow potatoes from true potato seed. It is wise to use heirloom potato varieties, as potato seed pods from hybrids will not produce good quality spuds.

To grow potatoes from true potato seed, you need to separate the seeds from the rest of the fruit. First, gently mash the berries, and then place in water and let sit for three or four days. This mix will begin to ferment. The resulting floating fermentation should be poured off. Viable seeds will sink to the bottom and should then be rinsed well and allowed to dry on a paper towel.

Seeds can then be labeled and saved in a cool dry place until planting season. The seeds should be started indoors in the winter since plants started from seed take longer to develop than those started from tubers.

Seed Potatoes

Small seed potatoes can be planted whole, but larger ones should first be cut into pieces with at least one eye or recessed dormant bud. The pieces should be blocky and 1-1/2 to 2 ounces in weight. If you cut each piece to the size of a large ice cube it will be about the right weight.

Seed pieces can have several eyes each, and be larger or smaller than recommended. Larger ones produce plants that yield a high number of medium to small potatoes. Smaller ones will yield fewer, but larger, potatoes.

While it may be tempting to plant smaller pieces in the hope of getting big potatoes, stick to the middle-sized pieces. Small pieces have less starch stored up to nourish the developing plant, so their food supply is quickly exhausted. Larger pieces have more energy to offer, which can help a young plant recover from an early-season injury. For example, if you plant very early in the season, a late frost could injure the plants after they’ve sprouted. Plants from a good-sized seed piece can continue to draw on the stored energy of the piece to recover more rapidly and resume normal growth.

The Wait Debate

There’s always talk around the neighborhood at planting time about whether to cut seed potatoes and plant them right away or whether to cut them and store them until the cut pieces heal over.

You can do it either way, but you may have more success if you cure the seeds after cutting them, giving them time to develop a protective covering over their exposed surfaces. Researchers suggest you store or cure the cut seeds for two or three days in a humid environment around 70° F. This will promote fast healing of the surface and keep the seed pieces from drying out. When you plant them, the protective covering will retain moisture and energy and serve as a barrier against rot organisms.

Other people feel you should plant the seed immediately after cutting. In a book for home gardeners, the U.S. Dept. of Agriculture urged cutting and planting right away saying, “Otherwise, viability will be lowered by loss of moisture and entrance of rot organisms.” This theory is good advice when the soil is relatively warm — when you’re planting late in the spring, for instance. In early spring, however, the soil is cooler and more moist — conditions favorable for rot organisms in the soil — so be sure to cure the seed pieces for a couple of days.

Protecting Cut Potatoes

There are other ways to protect cut seed potatoes, too. Sulfur powder is a natural, inexpensive seed protectant available at most drugstores. A couple of ounces protects approximately 10 pounds of seed potatoes. Put several seed pieces in a paper bag, add a tablespoon or two of sulfur and shake the bag. The powder sticks to the pieces and protects them from rot organisms in the ground. It will protect against rot in the ground and help give you a better crop. Follow directions carefully when using fungicides or any other chemical.

To avoid the controversy, order seed potatoes from mail-order companies or on-line that supply seeding tubers just the right size for planting.

How to grow potatoes you can harvest from summer to fall

Mounding and hilling are the time-tested ways of growing spuds. But if you’re only going to be growing a few, or if you love “new” summer potatoes, this simple method is worth a try.

Step one — Prepare the seed potatoes

Cut the potato into several 1-in. chunks, as in the photo above. Include an “eye” on each piece. This is the growth point where the new plants emerge.

Don’t cut the pieces too big. A smaller chunk of potato encourages the plant to get busy and put down its own, strong roots, rather than live off the stored foods in the seed piece.

And don’t try to get a lot of eyes on a single piece. Each eye will produce several stems. If too many grow together, they’ll compete with each other for sun and nutrients and make a shaggy mess.

Let the pieces chit, or air-dry, for 24 hours. This toughens the outer layer of the potato and helps it resist disease.

You can also give the potato pieces a light dusting of sulfur powder or Bordeaux mixture to help prevent fungi from attacking them. Shake the pieces in a bag with a small amount of the powder until the pieces are evenly coated.

We’ve found that the spuds will be fine without chemical treatments if the soil they’re planted in is dry and warm.

Check with your local extension service for the right time to plant potatoes in your area.

Step two — Prepare the soil

With this method, you don’t need to dig trenches or mound soil into hills. Just work a trowel full of compost into a square foot of soil in a sunny, well-drained area of the garden. The soil should be loose enough for the potato to send down roots easily.

Take a piece of seed potato and press it firmly into contact with the soil. Be sure the eye faces up, as in the photo above.

Step three — Mound up the mulch

Build up a 6-in.-deep mound of mulch over the potato. Oak leaf mold is excellent for mounding. Straw will also work, but may bring in weeds you’ll have to take care of later.

Water the mound gently to thoroughly wet the mulch. This will help it hold together. Keep the mound evenly moist.

As the vines start to peek through the mound, begin feeding them with a half-strength foliar spray. Use fish-emulsion or seaweed extract once a week until the flowers open, then stop feeding.

Mound additional mulch around the stems each time they’ve grown about 6 more inches.

Potatoes grow at the ends of stolons that the plant puts out wherever the stems are covered with mulch. So in time your plant will have tubers in several sizes within the mound.

Step four — Harvest potatoes

The best part about this method is that you can “rob” new potatoes, the creamers and steamers, without disturbing the plant. If that’s your goal for your potatoes, the time to go after the first new spuds is right after the flowers bloom, as in the illustration above. Just move the mulch gently out of the way and pop the new potatoes off the ends of the stolons with your fingers.

Only take about 20 percent of the new potatoes at a time. Let the rest remain to keep the plant from being stressed.

Continue watering the plants throughout the season to keep them producing new potatoes.

If you’d prefer to let the potatoes mature and get larger, stop watering them after the flowers bloom. This causes the plant to start concentrating on developing the potatoes. Then, in the fall, when the plant begins to die back, as in the illustration above, move the mulch away and harvest the full-grown potatoes.

Starting a new vegetable garden? Check out our guide before you do!

How Potatoes Grow

Potatoes are usually grown from other potatoes. You plant a whole, small potato, or a piece of a larger one for a new plant. The whole potato or cut piece has several slightly recessed, dormant buds or “eyes” on the surface. When conditions are right, these buds will sprout, whether the potatoes are in the ground or in a kitchen cupboard. The sprouts then develop into independent plants.

Starting From Seed

The cut potato piece or “seed” piece provides the new sprout or seedling with nourishment from its supply of stored starch.

After you’ve planted a seed piece, it usually takes one to two weeks for the main stem and first leaves to appear above ground. The root system develops quickly and begins to absorb nutrients as the food supply in the seed piece is used up.

Top Growth

The top, leafy part of the plant puts on a lot of growth in the first four to five weeks after planting. Then the main stem of the plant stops growing and produces a flower bud. When that happens, the plant will have as many leaves as it will ever have.

With proper sunshine, the leaves eventually produce more food than the plant needs, and the excess energy is channeled downward to be stored in the “tubers” — thick, short, underground stems — which we simply call potatoes. Irish potato tubers develop above the original seed piece, rather than below it like many other underground vegetables.

Storage

In general, the storage process starts five to seven weeks after planting, often when the plants have flowered. Some varieties will produce great potatoes with no flowering at all, but usually flowering is a sign that something is definitely happening underground.

Incidentally, potato flowers don’t produce any nectar, so they’re not visited much by bees or insects. The flowers are self-fertilized, and many potato plants produce small green seed balls about 1-inch in diameter, which contain up to 300 seeds. These seeds are mostly used by potato breeders.

When the tubers start forming, cooler temperatures are a plus. Years ago, research showed that fewer and fewer tubers were formed on the plants as the temperature went from 68° to 84°F. In fact, none formed at 84° F.

Best Weather

The best potato crops are produced when the daytime temperature is in the 60° to 65° F range, and when night temperatures are below 57° F. When the weather is hot, the top part of the plant respires heavily, reducing the amount of food material that can otherwise be put into storage in the tubers below ground. This helps to explain that while potatoes may be a summer crop up North, they’re a late winter, spring or fall crop in the South.

In a big potato-producing state like Idaho, for example, cool summer days and nights keep energy losses to a minimum. Plenty of starch is stored in the tubers, helping to make the Idaho potatoes terrific, big, mealy bakers.

Best Spuds

As potatoes enlarge underground, the outside layer of the tuber gets tougher and tougher, keeping moisture within the potato and protecting it from outside attacks by organisms that can cause rot.

This toughening of the skin continues even as the plant tops die, the signal to the gardener that the harvest is at hand. Potatoes can remain underground for a little while after the tops die, so that the last energy in the tops can be transferred to the tubers. If the outer skins can’t be rubbed off after the potatoes have been dug, they’ll store well

POTATO PLANT

Potato plants emerge from the ground 2-6 weeks after planting, depending on weather, location, and time of year. The plants grow quickly, and will begin to grow tubers just a few weeks after emergence.

After the plants emerge, the grower has to be very careful to keep his field thoroughly watered. Potato plants can survive periods of dry soil, but drought-stressed plants produce fewer potatoes of low quality. During the hottest weeks of summer, center pivot machines may run 24 hours a day, watering an entire field every 20-30 hours.

After emergence, growers must carefully keep track of the health and growth of their potato plants. They regularly take leaf samples and have them chemically analyzed for the amounts of essential plant nutrients. When the fertilizer they applied before panting starts to get used up, they see this in their leaf sample tests, and begin applying fertilizer to their growing plants. Toward the middle of the growing season, growers stop all fertilizing. This encourages the plants to put most of their growth into tubers for the second half of the season. Too much fertilizer late in the season causes plants to grow huge above ground, with very small tubers.

Many pest diseases and insects attack potatoes. Growers carefully watch their fields for disease symptoms and insects. Scientists track disease and insect populations throughout Washington’s potato-growing region, and provide helpful information to the growers. One of the most important pests of potatoes is late blight. This is the disease that caused the Irish potato famine of the 1840s. This disease can completely destroy a potato field, and can quickly spread to neighboring fields; everybody in the region must control it. Growers treat their crops to protect them from late blight using fungicides that stop late blight infection. They follow the recommendations of scientists who have studied and understand the biology of the late blight fungus.

The green peach aphid is the most important insect pest for potato growers. It is so important not because it directly damages plants, but because it carries a devastating potato disease called “potato leafroll virus” (like people, potato plants can get sick from viruses – but potato viruses cannot hurt people). This virus weakens potato plants and causes the tubers to have brown internal markings called “net necrosis.” Supermarkets and restaurants will not buy potatoes with net necrosis, so it is very important to growers to prevent it in the field. Similarly to late blight, scientists keep track of aphid numbers throughout the region, and keep the growers informed. When growers find aphids in their field, they have the field treated with insecticides. Some modern aphid-insecticides are incredibly targeted – affecting only aphids and a few close relatives, and are less toxic to humans than table salt. These insecticides preserve beneficial insects in the field, and are extremely safe for workers and consumers.

One important pest that many people will never have heard of is the plant-parasitic nematode. Nematodes are minute worms that infect plant roots and potato tubers. Nematode-infected potatoes are definitely not attractive, and growers cannot sell potatoes infected with nematodes. Many fields must be treated with nematicides to control these pests. Until consumers can accept these unnattractive, nematode-affected potatoes, growers will have to control nematodes.

A seed potato is a potato that has been grown to be replanted to produce a potato crop. It’s the usual way that potatoes are made available to farmers and growers – although it is possible to produce potato seeds (also known as True Potato Seed, TPS), it is unusual to do so.

A potato is a tuber, a way for a potato plant to store energy so that it can regrow next year. In spring, potato tubers will start to sprout new growth from growing points called eyes. Each potato has several eyes.

Although the potatoes in your fridge will start to sprout if you keep them too long, it’s not recommended to plant those in the garden, because they could be contaminated with blight spores and viral diseases. For the same reason it’s also not a good idea to let leftover potatoes (volunteers) sprout in your vegetable garden.

Seed potatoes are guaranteed virus free. In the UK many of them are grown in Scotland, where the climate doesn’t favour the aphids which spread virus diseases elsewhere. Some potato varieties are made available as microplants or microtubers – plants and tubers that have been produced in sterile lab conditions to ensure that they’re disease-free. This is usually done for heritage/ heirloom varieties, not the most popular ones. It’s also now possible to buy dual-purpose plants that grow both potatoes and another crop – e.g. the TomTato and Egg & Chips plants – but note that these plants will need extra feeding and watering to produce a good crop of either vegetable.

Shopping for seed potatoes is a lot like shopping for potatoes in the supermarket – ideal candidates are firm and free from blemishes. Later in the season they will start to sprout; it’s OK to buy seed potatoes that have formed short, green sprouts, but it’s not a good idea to buy ones that have formed long, white and spindly sprouts as these are very fragile and likely to break off when you plant them.

Seed potatoes are generally available to buy from late winter through to mid spring (January to April in the UK), although you can order them online/ mail order as soon as the new season vegetable seed catalogues start to arrive. Order early and you’ll have your choice of varieties; later on you may be able to bag a bargain, but you’ll have to make do with what’s left. Potatoes are such a popular crop, and there are so many varieties to choose from, that Potato Days are popular events where you can buy seed potatoes from the widest possible choice of varieties. Local nurseries and garden centres will stock a limited range.


How do I choose which potatoes to grow?

The potato varieties you choose to grow will depend on a lot of different factors, starting with your location and which varieties have been developed to grow well there. In many areas potatoes suffer badly from late blight disease, which can greatly reduce (or even eliminate) a crop. Choosing a variety with blight resistance, such as the Sárpo varieties bred by the Savari Trust, can save your potato harvest.

The primary distinction between different varieties is when they will be ready to harvest. In chronological order, the categories are: First Early, Second Early, Early Maincrop and Late Maincrop. Salad potatoes are generally early, waxy varieties.


First earlies can be planted from early spring (the end of February in the UK) through until late spring, although earlier plantings will have to be protected from frost. They produce small ‘new’ potatoes in about 10 weeks.

Second earlies are planted a month or so later, and take 13 weeks to produce a harvest, but the goal is the same – small, new potatoes.

Early and salad potatoes are ideal for growing in containers.

The Maincrop potato varieties are more suited to growing in the ground, and the aim is to produce larger crops of larger potatoes in 20 weeks. They can be planted from March (Good Friday is a traditional planting date, although the weather is not always suitable, through until late spring.

‘Second cropping’ seed potatoes are a bit different – they are planted in August for autumn/ winter crops (but must be protected from frost) around 11 weeks later.

Once you’ve decided which type of potatoes you want to buy, it’s down to choosing the individual varieties based on how you want to use them. Variety descriptions will include information on whether they’re good baked or boiled, mashed or roasted, or if they make the perfect chips (French fries).

You can choose from modern or heritage varieties, producing different sizes of potato, with different coloured skins – and even different coloured flesh! For most gardeners it comes down to a choice of which varieties grow well in their garden and the ones with the best flavour or that store particularly well.

Once you’ve chosen your seed potatoes, its normal to chit them, by setting them out in the light to grow short, green sprouts. This gives them a head start before you plant them out, and also prevents them from growing the delicate and spindly white sprouts they would produce when kept in the dark.


Whilst you’re waiting for your seed potatoes to sprout, there’s a whole range of basic gardening advice to get your teeth into. Or you could get adventurous and learn about some potato alternatives. Once you’ve grown your potatoes, I’ve got a lovely recipe for Simple seasoned wedges over on my food blog – or you could just try it now!


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