Potatoes in Your Vegetable Garden - How to Grow Them
Potatoes prefer cool conditions (53 - 75 degrees F), deep well drained fertile loam and sandy loam soils with a pH of 4.5 to 7.5. Good levels of soil organic material is good, but really high organic levels and manure can be detrimental to potatoes. Potatoes can grow in other conditions than these with adjustments and at time a yield reduction. Varieties differ in their needs and variety selection can overcome less than optimal conditions at times.
Seed
Good seed can be the single most important factor to good potato yields. Potatoes, unlike most crops, the true seed is not planted. Instead the tubers are planted. The right variety for your conditions and needs is important. Potato seed in good condition is also very important. "Aged" seed is seed that is soft and flaccid and a result of poor storage conditions. Aged seed will produce more stems, a plant that will die early and produce less. Seed needs to be stored in a dark, moist and cool to cold area (depending on the length of storage). Modern potato production seed storage are temperature and humidity controlled to store the seed at 95 - 100 % humidity and 36 - 42 degrees F. Tubers from the grocery store may have been treated with a sprout inhibitor and thus not grow properly, thus this is not a good source of potato seed.
Seed size should generally be the size of a hen's egg or 2 to 3 ounces and planted whole. Large tubers can be cut before planting, but this can lead to spreading diseases and losses to other soil diseases. Applying lime to the cut surface can help reduce seed decay problems. The warmer the area the less advisable it is to cut seed tubers.
Warming up the seed tubers can help with a faster emergence and avoid some seed piece and early sprout soil disease problems. Allowing the seed tubers to sprout a bit is a common practice in Europe and can increase the stand and yield. This pre-sprouting or chitting is simply spreading the seed tubers in indirect light in a warm area (70 degrees F). Seed should be planted when sprouts are 1/4 to 3/8 inch long. Don't allow sprout to get too long or you will weaken seed and sprout will break off too easy.
For a catalog of seed available to home gardeners click here.
Soil Preparation
Its important to loosen the soil well for a potato crop. Work the soil to a depth of 18 inches if possible. This allows good root and tuber development. Some humus can be very beneficial for potato production. Potatoes prefer slightly acidic soil, alkaline soil can lead to somewhat scabby potatoes. Potatoes respond to calcium and a balanced fertilizer program of nitrogen, phosphorus and potassium. 15-15-15 would be a good commercial fertilizer to use at a rate of 1 - 2 lbs. per 100 square feet which is 33 feet of row at a 36 inch row spacing. Some varieties prefer splitting the total nitrogen application. For example 1/2 on at planting and 1/2 applied at hilling. Some of these varieties include: Norkotahs, nugget, Burbank, and legend. Consult the varieties profiles for details. In this case apply 3 to 7 ounces per 100 square feet ammonium sulfate before hilling and work it into soil with a how while hilling.. If you want to grow organically, working in 100 lbs. of compost in 100 feet of row will produce a good potato crop. In both cases work the fertilizer in well before planting. Fertilizer can also be banded beneath the seed at planting time which works very well in alkaline soils.
Planting
Potatoes don't grow in soil temperature less than 45 degrees F. Optimal soil temperatures are 50 - 70 degrees F. Seed tubers can rot in wet cold soils, so wait till it warms up enough and pre-water before you plant, but wait 2 - 3 day after watering or a good rain before planting. Potatoes can be planted before the last frost date since their first 25 - 40 days are spent underground protected by the soil from frosts. If the frost burns the plant down, it will regrow from the seed tuber, but this takes time and plant energy. Three feet between rows is generally the best spacing, but this can be shortened to 32 inches. Spacing between plants is generally 12 inches, but in the case of red potatoes where you want smaller tubers plant them closer at 8 inches between seed pieces in the row.
Dig a trench 6 to 8 inches. If you are going to band fertilizer, apply the fertilizer in a band in the trench and cover with 2 inches of soil. Place the seed in this trench, it doesn't matter which side is up with potato seed tubers. Cover the seed with 3 - 4 inches of soil and press the soil down firmly for good soil seed contact. There will still be a slight trench when you're done.
Cultivating and Hilling
Hilling is very important for good tuber development. The new tubers form above the seed tuber so more soil is needed above the seed. You want 6 - 8 inches of soil above the seed when finished hilling. Planting the seed this deep at the start can lead to poor emergence of plants and disease problems. Sprouts will emerge in 2 weeks or so and plants will emerge shortly afterwards. When the plants are 6 - 8 inches tall hill soil around the plants, careful no to cover too many leaves. Another final hilling may be needed in another 2 - 3 weeks. Make the hills broad and flat so the tubers have room to develop and not push out of the hill later and turn green. Don't hill after tubers are 2 inches long. Fertilizer (nitrogen) can be applied right before hilling and incorporated into the soil during the hilling process. This can benefit some varieties greatly. During the hilling process weeds are removed and covered with soil.
Watering
Potatoes have little drought tolerance mid-season so irrigation may be necessary. After planting and when the plants are small, make sure the soil is moist, but too much water at this point can encourage destructive soil diseases. After the plant is 12 inches tall and during tuber bulking (enlargement) it is important to maintain good soil moisture. Water or rain needs to be applied every 3 - 4 days is small amounts. Over-watering can cause fertilizer losses, certain diseases like leak and yield and tuber quality reductions.
Diseases
Most potato diseases are seed borne so planting disease free seed will eliminate most potato disease problems. Certified potato seed has been inspected and has to conform to regulated low disease levels. Staring with good disease free seed is very important in potato production. These seed borne diseases have no cure once infected. For more information on potato diseases click here.
There are two important potato diseases that spread during the season - Early blight and late blight. For more information on each of these disease click on their name. There control is basically the same - fungicides applied on a regular basis after plants form different rows begin to touch. If you garden is isolated from other potatoes and you rotate your ground (plant the potatoes in a different place in the garden each year), fungicides may not be needed. Fungicides are preventative only. Organically elemental sulfur dust and milk sprayed on the plants can help, but these are only a partial cure. A strong healthy plant is also one of the best disease controls.
Insect Pests
Again a healthy plant helps a plant resist insect damage. Insect pests that are a major concern are Colorado potato beetle, leafhoppers, aphids and armyworms. For descriptions and control measures of potato pests click here. Organic control of insects includes:
For a guide to convert application rates on a per acre rate to a garden size rate click here.
Harvesting
Potato varieties are generally done growing 90 to 150 days after planting depending on the growing area and variety. Some varieties are determinate and will quite growing after a certain number of days. Others will continue growing as long as the weather and plant health permits. Generally when the tubers are big enough its time to finish the plant off - just dig a few fresh tuber up and eat them fresh. Frost is a good way to finish the plants. Tubers must mature or cure if you want to store the potatoes for any length of time. Tubers must sit in the ground for 2 - 3 weeks to harden the skin on the tubers. If the plants are not dying 2 - 3 weeks before your want to harvest them (or tuber size is good) kill plants off by chopping or cutting plants off at the soil level.
At harvest time dryish soil is definitely an advantage since tubers come up a lot cleaner, but too dry and it will be hard to dig. Avoid scuffing or injuring the tubers during harvest or storage and disease problems could occur. Harvest is best in the morning when the tubers are cooler. Place a fork or shovel at the edge of the hill and lift up the hill carefully, avoiding cutting tubers. If the soil is wet, allow the tubers to air dry before sacking them. Field grade or separate to potatoes before sacking them into big and little tubers. Separate any diseased or damaged tubers at harvest and store them apart. These tubers may rot and also rot the good tubers around them in a sack. Its important to cool the tubers down fast and remove the "field heat" for good long-term potato storage. Each plant should produce 3 - 4 lbs. of tubers.
Storage
Potatoes keep best when kept in the dark at 36 to 40 degrees F at enough humidity so they don't dry out. The tubers need to be kept aerated as well - remember the tubers are still alive. Light promotes greening and a bitter taste. Warm promotes early sprouting, and low humidity causes the tubers to shrink and shrivel. Burlap sacks or slotted crates and baskets work well for storage containers. Don't stack sacks too deep or poor ventilation and bottom tubers getting pressure bruises will result. A good root cellar is the best potato storage. Partially heated basements, crawl spaces, garages and back rooms can be used as well. A refrigerator can work as long as the temperature doesn't fall below 36 degrees F and especially below freezing. Below 36 degrees the tubers will get sweet.
Basket or Cage Method of Planting Potatoes
This method each plant has its own planter. Use container about 18" x 18" x 18". Fill with good rich soil. Plant one seed potato in each container. Make a hole 6 - 8 inches deep and cover with 4 inches of soil. As the plant grows fill in around the base of the plant. Keep watered as the plants needs it. Water requirement will be greater in these container plants. Yields should be greater. This is a great way to produce a lot of potatoes in a very limited space.
For another online guide to growing potatoes in your garden click here.
Note: This information should only be used as a guide. Adjustments for local conditions must always be made.