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SEED POTATO PLANTING GUIDE - Organic Heirloom Gardens

SEED POTATO PLANTING GUIDE - Organic Heirloom Gardens

Posted by Organic Heirloom Gardens on Feb 14th 2018

Cut The Seed Potato Or Leave It Whole?

An in depth study on Russet potatoes states:

“Cut seed produced a higher yield of tubers > 51 mm diameter in comparison to all whole tuber seed sizes, with the exception of the 28 and 56 g sizes. In terms of total yield, the 28 and 42-g whole seed tubers yielded significantly less than all other seed sizes examined”.

  • Whole & cut seed both produce potatoes to harvest though varying in size & yield.

In the study, cut seed was producing a higher yield of LARGE tubers over 51mm at harvest in comparison to ANY sized whole seed potatoes in the study except two.

  • In terms of total yield weight, cut seed produces just as much as whole seed on average.
  • Do NOT confine yourself to thinking a “seed potato” is one certain size & planted whole.

Note: Always allow cut seed potatoes to “heal” or “scab over” before planting. After cutting let them sit out for several days until they dry some on the outside and form a new “skin”. The leathery dry surface that forms helps protect the cut seed from disease. Use a sharp blade to make slices, cuts with dull blades stress the seed more.

What Size Should A Seed Potato Be?

(In Weight - Cut or Whole)

Nora Olsen, Ph.D., extension potato specialist at the University of Idaho Kimberly Research and Extension Center and president of the Potato Association of America tells

“We do not recommend planting a seed piece or whole tuber smaller than 1.5 ounces,” “If you plant a whole seed or seed piece below this size, the resulting plant may not be as vigorous and large as desired and may yield fewer and smaller tubers.”

  • Your size should always be over 1.5 oz., cut or whole.
  • Try to get the weight between 1.5-3 oz.
  • Over 3 oz. still works fine, you just use more seed material per plant.
  • Be practical, if it is a larger potato you want to cut it to make several smaller seeds.

How Many Stems Per Seed/Plant?

(Cut or Whole)

A study at the University of Idaho College of Agriculture states:

“For Russet Burbank, an average of 2.5 to 3.5 stems per plant is considered optimum for maximum performance in commercial plantings. The number of eyes per seed piece influences stem numbers per plant.”

This can vary a bit across the different varieties but it holds pretty true. If you have about 2-4 stems coming up from a plant you will not have overcrowding. This is going to give the plants enough room to produce large tubers. If you have more stems you are going to obviously produce more potatoes, however they will be smaller in size due to crowding.

Big Potatoes - 2-4 Stems per seed piece. You will get more large potatoes per plant.

Smaller Potatoes - 5+ Stems per seed piece. Smaller potatoes but more of them.

Note: Eyes/stems should always be facing the sky. Potatoes grow upwards not downwards.

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Seed Age & Aging The Seed (Or Not)

Seed potatoes will come to you in various stages of physiological age and are impacted by many factors in the aging process. This could turn into a very in depth part of the planting guide, but I just want to try to cover a few points here.

My Seed Potato Doesn’t Have Enough Eyes Sprouting When I Received Them!

Not to worry, this just means your seed potato is young in physiological age. Some people like to have a bit of growth or even A LOT of growth coming out of the eyes before planting. This is actually not needed.

Here is a break down of what seed age young or old means. Both have their advantages.

Young Seed - Slow emergence, Fewer stems per hill, Low tuber set, Longer tuber bulking period, Long tuberization period, & Larger tubers at harvest.

Old Seed - Rapid emergence, More stems per hill, Higher tuber set, Shorter tuber bulking period, Uniform tuber set, & Smaller tubers at harvest.

Aging The Seed - If you want more growth from the eyes before planting this is not hard to achieve. Place your potatoes one layer deep in cardboard boxes. Place the boxes in a closet or other dark place. You want the temp to be at least 55-60 degrees or even warmer. This is going to speed the aging of the tubers and cause growth. The cardboard keeps the air more dry to avoid promoting mold. Check on the potatoes in about a week or two, growth will have begun.

NOT Aging The Seed - The best temperature to store seed at to avoid aging is 38-40 degrees. Keeping the temperature steady is also important. Big changes in temperature will cause the seed to age more rapidly.

Planting - When, Depth, Spacing, Trenches, & “Hilling”

There are several methods of potato planting. No matter which one you use, you want to follow these basic guidelines.

When To Plant - Planting for potatoes can start about 3-4 weeks before your last frost. You need to be very careful with this if you live in an area prone to refreeze late in the season. The reason you can plant about a month before your last frost is that the plants are going to be covered by soil and not exposed to the freezing temperatures. You need to think about where you live and how the weather works there. If you are having weeks in the 40s and 50s where temps barely dip below freezing at night, THAT IS IDEAL! If you are still having temperatures that do not CONSISTENTLY get over freezing in the day time, or temps still falling into the lower 20s and teens at night, THIS IS NOT IDEAL!

Seed Depth - Seeds should be placed 4-6 inches in depth and covered with soil. Ultimately you want the potatoes to be about 8-12 inches under soil, eventually. If your soil is ideal and VERY loose you can dig them down to that depth, place them and cover them with dirt. However if it is not VERY loose soil it is NOT recommended digging your trench or hole too deep into compacted soil. This is going to make it much harder for your plants to produce tubers.

Plant & Row Spacing -

Larger Potatoes But Less Quantity Per Square Foot

  • Row Spacing @ 36 inches
  • Plant Spacing @ 11-14 inches

Smaller Potatoes But More Quantity Per Square Foot

  • Row Spacing @ 27 inches
  • Plant Spacing @ 7-9 inches

Trenches - The most common method of planting potatoes is using a trench forming a row. Unless your soil is VERY loose you want to dig this trench down only about 4 inches deep. All the soil you dig out should be loosened and broken apart before covering up your potato seed. Potatoes depend on VERY loose soil to produce tubers properly.

Hilling - After planting your potatoes and covering them up with about 4-6 inches of loose soil you will need to let them grow for a few weeks until the leaves start to pop out the top of your trench rows. Let them get about 4-6 inches out of the top. At this point it is time to do what is called “hilling”. You are going to loosen and break up the soil on either side of the rows and pile it onto the rows to the point to where only the top leaves are sticking out. By doing this you will be causing what looks like a hill to form. This is also true if you have used a non-trench/row method. You want to make sure any potatoes that grow are completely covered by soil. If they are exposed to the sun they will turn green and have a bitter taste.

Note: In a home garden bringing in bags of loose soil for covering potatoes when first planted and/or hilling is a viable option. Some people also use straw, sawdust, and other mixes to achieve the loose soil that is desired. Make sure you do your research if you choose anything out of the ordinary.