University of Vermont Extension 
Department of Plant and Soil Science

Anytime News Article


Dr. Leonard Perry, Extension Professor
University of Vermont
In a recent survey of Vermont gardeners, only about one third grew their own potatoes.  Yet this vegetable is easy to grow by several methods, and following a few tips.  Growing your own you can have varieties that you wont find elsewhere, ones with better flavor, and ones that you know are safe to eat. 
Commercially, in large fields, growers can be faced with several problems that they often control with chemicals.  This gives store potatoes a listing on the “dirty dozen”—those vegetables reported to contain the most pesticide residues (  Of course buying from local organic farmers you can avoid such concerns, but even they may use organic chemicals you wouldn’t need in a home garden. 
There are so many varieties, too, that you just won’t find in stores or even from many local growers.  Potatoes can be grouped by use, size, or color and vary in texture and flavor.  The russet types are ones you see in stores with the brown skin, large elongated shape, and are used for baking.  “New” potatoes are ones harvested small and immature, and aren’t necessarily red as often believed.  Red potatoes (on the outside) can be red, white, or yellow on the inside.  White potatoes (on the outside) can be white or yellow inside.  Then there are purple potatoes, both outside and inside, which may turn blue on cooking.  Finally there are the fingerlings, shaped more like fingers or stubby carrots.
Potatoes can be grown from true seeds, similar to tomatoes, in which case you’d want to sow them indoors about 8 weeks before the last frost date when you’d plant outside.  Usually though they are grown from “seed potatoes” which aren’t seeds but pieces of a potato with sprouts, buds, or “eyes”.  You’ll find these in garden catalogs and stores in spring, but not on the seed racks!  Look for certified disease-free seed potatoes.  Don’t use store potatoes, as these usually have been treated with an inhibitor to prevent sprouting, and might have diseases.
Potatoes are a storage organ of the plant called a “tuber”.  For golf-ball sized tubers of seed potatoes, you can plant them directly.  Large tubers should be cut into pieces about 2-inches thick, or weighing about 2 ounces, and containing a couple of the new shoots or eyes.  These should still be short, just sprouting, and not with stems on them yet.  If they have started growing, handle very gently to avoid breaking these tender stems.  If cutting a large tuber into sections, before planting allow the pieces to harden-off in a cool (55 to 65 degrees F), well-ventilated area for a day or two. 
Plant outside about 3 weeks before the last frost date, about the time daffodils are blooming and soil temperatures are at least 50 degrees (F).  While frost won’t hurt the seed pieces in the ground, it can damage new shoots above ground.  Cover these with a frost cloth or similar protection if needed. 
The principle to keep in mind when planting is that you want the new potato tubers that form to be in the ground, out of the light, so they don’t turn green (this makes them bitter and slightly toxic).  There are several methods of  keeping them in the dark under soil.  Traditionally, seed potatoes are planted about 3-inches deep in trenches, about a foot apart, and with rows about 3-feet apart.  Then, as the plants grow, you mound or “hill” up soil (or compost or straw) around them, covering about half to two-thirds of the plant.  If using the straw method, first cover with a couple inches of compost before applying subsequent straw layers.  Straw may
not be good to use if you have mice in your yard or nearby, and may result in lower yields.          
A variation on straw hilling begins with a foot-deep trench, planting the seed potatoes in the bottom about three inches deeper.  As plants grow, first add a few inches of compost, then just straw, filling in the trench. 
Short on space?  Don’t want to go on a treasure hunt digging later in summer?  Or do you only have full sun, which they need, not where you might plant in the ground?  Then consider planting in containers.  This is the method I use, with potatoes growing in thick felt-like bags just for growing such crops.  Although bags hold about 15 gallons of mix, I only use about 12 gallons.  I start with about 6 to 8 inches of a compost and potting soil mix, then as the plants grow add more until the bag is about 3/4 full.  A square wooden frame or wire mesh cage could be used similarly.
Although a low pH or acidic soil is recommended by some to avoid scab disease, potatoes often grow well over a range from 5.0 to 6.5, with 5.5 to 6.0 perhaps ideal.  Soils should be well-drained and not soggy.  Potatoes need some fertility, but not too much, which will result in mainly leaves and shoots.  In a fertile soil, compost may be all that is needed.  Avoid manures as these can lead to scab.  Otherwise, add a garden fertilizer according to soil test recommendations.  Lacking these, you might broadcast over the bed and mix in a quart of 5-10-10 fertilizer per 25 feet of row.   A main key to good yields is keeping plants well-watered, especially after bloom until shortly before harvest, while new tubers are forming.  Mulches help.
One main disease with potatoes is a bacterial one called “scab” from the appearance of the corky dark lesions on the surface.  Potatoes are still edible but must be peeled.  As already noted, avoiding manures and alkaline soils help to prevent this organism from growing, as does proper watering.  Avoid planting potatoes in the same spot for three years (called “crop rotation”), or where other root crops such as carrots, beets, and turnips have been planted.  Some varieties that are resistant to scab include Russet Burbank, Norgold, Red Norland, and Superior.
A fungal disease potatoes can get, and in fact spreads to related crops, is late blight.  This is the famous disease of the Irish potato famine of the 1840’s.  Crop rotation helps with it, as well as other diseases, including not planting in the same area as tomatoes, peppers, eggplants, and strawberries for three years.  Don’t leave any tubers in the ground or save them from previous years if late blight has been present. Also, use certified disease-free seed potatoes.  There are sprays for this disease, including organic ones.
The main insect of potatoes in general is the pretty, somewhat rounded Colorado potato beetle.  Watch for it soon after the first leaves emerge, and handpick off.  Look under leaves for clusters of the bright orange eggs, and destroy these as well.  These hatch the larvae that eat the leaves.  Covering plants with floating row covers (very thin fabrics sold as this) goes a long way to keeping this beetle away, as well as other insects such as leafhoppers, flea beetles, and aphids.    

You can harvest “new” potatoes about 2 months after planting, mature potatoes for storing when the tops yellow and mostly die back—about 4 months after planting, or after killed by fall frosts.  Gently lift from soil with a garden fork. Brush soil off the tubers but don’t wash them until ready to eat.  Store at high humidity (75 to 90 percent) and cool (40 to 50 degrees). 
Store in a root cellar or similar location at 40 degrees or below (but above freezing).  Mine, stored in very slightly moist compost, last well for 6 months or more.  Some varieties stored just above freezing may become sweeter.  Leaving them out at room temperature for a few days may help if they are too sweet to taste.  Before cooking, cut off any green or damaged areas.

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