The Environment Potatoes Prefer
Potatoes require full sun to grow. Because they are aggressively rooting plants, storing larg amounts of mass in the soil, they will produce the best crop when planted in a light, loose, well-drained but moisture retentive loam. Potatoes prefer a slightly acid soil with a pH of 5.8-6.5..
Fortunately, however, Potatoes are very adaptable, and will usually produce a respectable crop, even when the soil conditions are less than perfect.
Potatoes Need Rotation Just Like Tires Do
Potatoes should be rotated on a 3-year program. Additionally, they should not be grown in the same area that any other Solanaceae or night shade family member has grown. This would include common food plants such as peppers, and eggplant.
Where To Get Seed Potatoes
I find saving my own potatoes is best. I get the healthiest potatoes that way. I prefer not to cut them, so I look for potatoes that are the size of an average hen's egg .
The best place I have purchased organic seed potatoes has been a company called Wood Prarie Family Farm.
Preparing Your Potatoes For Planting
A week or two before your planned potato planting date, set your seed Potatos somewhere where they will be exposed to some warmth (between 60 and 70 degrees F.) and lots of light. This will induce them to begin sprouting.
A day or two before planting, use a sharp, clean knife to slice the larger seed Potatoes into "seeds". Some folks dust sulfur over the cuts, but I usually don't. Each seed should be approximately the size of a hens egg, and must contain at least 1 or 2 "eyes" or buds. Smaller Potatoes that are egg size may be planted whole. In fact, I simply save potatoes for seed potatoes that are that size, so I don't have to cut any open and take the chance of diseae taking hold. In the next day or so, your 'seed' will form a callous over the cuts, which will help to prevent it from rotting once planted.
If you want lots of smaller potatoes, let all the sprouts stay on the potato. If you want bigger potatoes only leave a couple of the sprouts on the potato. Basically, the more sprouts coming out, the more potatoes that will be grown and if they have to share energy, they get smaller.
Planting Your Potatoes
Potatoes can be planted as soon as the ground can be worked in the early spring, but you must use good judgment. Potato plants will not begin to grow until the soil temperature has reached 45 degrees F. Potatoes won't grow well in hard, clay type of soil. They need to be able to stretch their legs easily and move around. Clay soil will also hold the water in and may lead to rot. The soil should be evenly moist, but not wet or soggy. If the soil is waterlogged when you dig, not only will you risk "caking" the soil, your seed Potatoes will probably rot before they even get started. Potatoes can tolerate a light frost, but you should provide some frost-protection for the plants when they are young. This can be a loose covering of straw, or a temporary plastic tent. (Be sure to remove or ventilate the plastic on sunny days!) If you plan to store Potatoes through the winter, you can plant a second crop as late as June 15.
Space the potatoes about 12" apart. Some potatoes have heavy set of potatoes and they need 15" - 18" to allow the spuds to get fully sized up. Place the sprouts or eyes facing up. The eyes are where the sprouts come from. Those sprouts will be the stems of the potato plant. Place them 4" in the ground. As they grow, you will hill up the area around them.
Some people plant potatoes in the fall. However, depending on how deep the ground freezes that might not work. Additonally, rodents may eat them all if you have a lot of rodents in the ground. I have lived mostly in areas where you can plant fall potatoes, but I also have had such a serious rodent issue, that I have had to create raised beds with 1/4 inch hardware wire attached to the bottom of the perimeter boards, to keep rodents from eating my roots and tubers I plant. For people who have potato beetles, and lack the rodents and hard winter freezes, they say planting in the fall is great as there are rarely potato beetles in the spring when they are able to start harvesting the young, new potatoes.
If you do plant in the winter and you have a lot of rain, you might want to consider making a ditch alongside the potatoes at a deeper level than you plant the potatoes. This will move water away from the potatoes and keep them from rotting in the winter.
I usually mix a little bit of epsom salts and if needed, phosphorus and boron. I live in an area with no boron. Additioinally, I add some compost. Not green compost but well made and cured compost. Potatoes don't like excessive nitrogen, so be careful or you will get scab. They do great with some compost though.
When the plants are 4-6" tall, begin to make a hill of dirt around them. The potato tubers will grow in this hill. Try not to cover the potato leaves up. I usually have a hill 10-12" deep. Another way, I have done this is to dig a hole down about 8-12" down, and put the potatoes in there with a little soil over them and add the dirt from beside the hole as they are growing. The potatoes in the photo to the right were grown this way. After adding dirt, the ground is flat rather than hilled up, if you use this method. It is more work to collect them at harvest though.
Besides soil, I have used straw or leaves to cover them, but find too much sun may get through the straw, so be careful to use thick straw if using it rather than soil. I have also added straw with dirt on top, boxes on top, basically, anything to keep the sun off the tubers.
Usually, I don't use much to feed the potatoes unless I have poor soil. I add some seaweed to all my soil. The potatoes get some too. They get a little compost, but not much. That usually takes care of their feeding needs. If necessary you could add some type of foliar spray on the leaves such as seaweed tea, liquid fish fertilizer or aerated compost tea. Make sure they have enough calcium, phosphorus and boron in the soil. You will need to have a soil analysis or leaf analysis to know what is needed. I get soil analysis in a new location but once I know what is needed in an area, I rarely look again.
Potatoes like to have regular water while growing, but don't make them soggy. When the foliage starts to turn yellow and die back, stop watering them.
Potato Problems and Diseases
Be sure to only use only certified seed Potatoes! Don't use your potatoes from the grocery store or you may introduce disease into your garden. Potatoes are susceptible to several serious diseases. Even though the Potato you see in the supermarket may appear healthy, they should not be used for your seed. If you had disease in your potatoes, it might be time to get new seed from elsewhere and don't forget to grow them in a new location.
Certified seed Potatoes are disease free, and have been selected to give you the best results with the highest yields. Certified seed Potatoes are available at most quality nurseries and garden centers. There are several different varieties of Potatoes to choose from
Pests And Diseaes
This is a plant I have little trouble with. Rotating my crop and not regrowing any night shade family plant in the same area for three years minimum is probably why. I suggest you do the same. Some people have trouble with potatoe beetles, but I have been lucky so far as to not have seen them. If you see a mass of orange eggs on the bottom of a leaf, that is them and crush them quick. If you see adults or larva they also need to be crush or disposed of in some manner.
I find scab tends to happen if I over-fertilize the potatoes, so I don't give them as much compost as other plants.
They were exposed to sun. This also means they may have high solanine in them which is poisonous. It is best not to eat green potatoes.
Potato Harvest - The When
You can harvest potatoes to eat at any time after the tubers start to develop. I love new potatoes, but usually wait until they get bigger. The tubers are there about the time that the plant starts blossoming. You can dig into the hill a bit and steal a few potatoes at this point. Be sure to recover the tubers still left. You don't want the sun getting on your potatoes.
For storage potatoes, don't harvest until at least two weeks after the vines have withered and look dead. This will allow the potato skins to thicken up. If it is going to rain hard, you may have to harvest early and allow them to thicken outside of the ground.
Potato Harvest - The How
I like to use a spading fork, but the best tool is my hands if the soil is easy to move. This way, I don't nick them with a shovel or sapding fork. You want to handle your crop very gently so they do not get a cut or a bruise.
As you are removing the first potatoes, look at them and make sure the skin is thick and does not rub off easily. If, the skin is not thick, they are not ready to harvest. A thick skin will protect them in storage.
Make sure they cure in a non-sunny area. In fact no light is great. I have put them in a breezeway outside and place a few layers of newspaper over them to keep it a bit dark. Too much light will turn them green, and sunlight exposure also means they may grow high solanine content, which is poisonous. You have to assume a green potato has solanine in it, since you are not going to test it. Therefore, keep the sun off of your potatoes if you don't want to have to throw them away. During the curing time is when any wounds created by digging them up can be healed so they will store okay.
Wound healing and curing should be done at about 60-65, with high humidity and will take about 10-20 days. Without doing this you can get rot if put into storage in a rapid cooling environment, especially if in the absence of adequate air. This can cause black spot and other potato damage.
The skin will harden up a bit more in the curing process and if any of the potatoes had thin easily rubbed off skin, the curing process will be their only hope of getting tougher skin. When the skin looks strong and protective, I rub off any excess dirt, but don't rub too hard. Any potatoes that have wounds that did not heal, or they looked damaged, and/or diseased in any way, are either moved to the compost pile, or if edible, to the table.
Using The Dirt As Storage
Some people will leave them in the ground and harvest them as they need them. This works fine if the ground is relatively dry, you don't have rodents that eat them, and the ground is not going to freeze. They can take a light frost, but get them out before freezing weather starts.
Storage temp under 45 degrees F. will increase sugar formation. The high sugar will cause darkened potato chips and fries.( Some varieties recondition from sugar to starch better than others.) 40-45 degrees is best long-term storage for potaoes. For seed potatoes store at 38-40 F for less weight loss and sprout control. They need 95% humidity at all times. At temperatures below 38 F, potatoes are chilled and tend to become too sweet for most uses. For people with really good refrigeration control they will store at 38-40 for general storage, but in most home refrigeration, you may not have good control and it may dip too low and you get lots of sugar formation, so I keep it around 40-42 myself. I have used everything from closets to refrigerators to store potatoes. If you store outdoors, be sure they don't freeze. I once had potatoes in a refrigerator outside and forgot they were there when it freezed. I should have taken them into my garage as they were all bad.
Different types of potatoes may be handled slightly differently. So, check on conditions needed for your variety. You can find detailed directions for how to handle storage of potatoes depending on what type they are and what they will be used for.
Seed potatoes are usually held at 36 to 38F and high humidity.
Exposing cold potatoes to warm outside air for long will cause a layer of free water to condense on the tubers. This can induce rot.
Do not expose tubers to air at or below freezing.
Potatoes usually do not sprout until 2 to 3 months after harvest even at 50 to 59 F. However, after 2 to 3 months of storage, sprouting can be expected in potatoes stored as cold as 39 F and much more so at 50F. Limited sprouting does not seriously damage potatoes for food purposes.
Humidification, CO2 and Oxygen
A humidity of 95% reduces weight loss and shrinkage markedly. Humidities of 80 to 85% generally results in better quality regardless of the end use. In reality this is not something most home growers can set up, but putting bowls of water in the refrigerator can help a bit. Using a humidifyer is dangerous for your building usually, so I have found simply boxing up my potatoes in a box with little room left and putting them into appropriate cold storage does a good job of keeping them from drying out. The box keeps the humidity up but does not decrease the air flow enough to cause other issues. I open the box often to get potatoes (I rebox them into smaller boxes as needed) and this also ventilates them, removes CO2 and provides oxygen for respiring tubers.