growing potatoes organically: when and how to plant, hill and harvest

Raised bed of potato plants A FRIEND I BUY seed potatoes with and I were scratching our heads as we filled out the order form, blanking on the line where it said “preferred ship date.” How early do we want them to arrive, we asked ourselves as we do every year. Time for a review of that and other questions about when and how to plant, hill and harvest potatoes. (That’s a row in my raised beds here, seen in late spring one recent year.)

Many companies ship extra-early, based on rough frost-date estimates for each area that may not be exactly what’s going on at your place, but is that really when I want the starts to arrive? I asked for advice from Alley Swiss of Filaree Garlic Farm, a longtime certified-organic farmer in Okanogun, Washington, whose main crops—garlic, shallots and potatoes—are favorites in my garden, too.

(Disclosure: I’m proud to have Filaree as a seasonal advertiser from time to time. You might recall the popular garlic-growing Q&A we did together last year; I’ve learned a lot from our ongoing conversations–including that it’s OK to wait a little while for the seed potatoes to arrive.)

potatoes dug from the garden

how to grow potatoes, with alley swiss

Q. When is the right time to plant—is there a cue in nature to remind us, or a soil temperature or calendar date we’re looking for?

A. At the earliest, I recommend planting two to three weeks before your average last frost date. Seed potatoes can rot if planted too early in cold water-logged soil.  If your potatoes do get a heavy frost after they emerge, they will put up new shoots, but every time they die back they will produce a smaller and later harvest.

I like to wait for the soil to warm up a little at which point they emerge quickly and grow steadily without stress.  Late March to early May is a good time to plant potatoes in the northern states.  In the warmer areas of the South they can be planted in late fall or early winter.

Where I farm the local point of reference is to plant your potatoes when the snow is almost melted off the mountain.  Whether it’s the first dandelions blooming or a particular bug emerging; if you talk to gardeners where you live they will probably have a local reference, too.

Q. Sometimes when seed potatoes arrive, some are nearly a tennis ball and some are mere eggs.  Should I cut the larger ones up, and do I have to let them callous before planting if so?

A. Many people choose to cut their larger sized-seed potatoes into pieces.  The advantage of doing this is your seed will go further and likely produce a higher overall yield.

If you do choose to cut your larger potatoes, make sure and leave at least two “eyes” for every piece.  Use a clean, sharp knife to cut the potato into several large pieces shortly before planting.

Leaving the cut pieces in a cool and humid space overnight will give them enough time to callous before planting.  The callous will help prevent infection from soil contact.

We plant our seed potatoes whole to minimize worm damage.  If you have problems with wireworms, maggots or other pests, planting whole potatoes may be a good idea. Pests are attracted to the juicy exposed flesh of a cut potato.

Q. I have read so many variations about soil prep for potatoes. Is there something they do want, and anything they don’t? (For instance, I’ve read to avoid using manures on the potato bed.)

A. The ideal soil for growing potatoes is a loose and deep loam that holds moisture and also drains well.  Luckily, for those without “ideal” soil, potatoes are hardy and adapt well too many difficult soil types.  Lots of organic matter is recommended for the best yields. It is best to incorporate organic matter or compost into the soil in the fall so the soil has time to balance the added nutrients.

Fresh manure can activate the pathogen “scab,” which makes for unsightly, yet still edible, potatoes.  For this reason I use only well-composted manure when preparing soil for potatoes.  If you do not have access to composted manure, a well-balanced fertilizer can be used (I use an organic 4-2-2).  Too much Nitrogen will delay root production and you may end up with huge plants with little potatoes.

Q. So I’m ready to plant, following your above prep guidance. Now what? Proper depth and spacing—and is it the same whether a big baker or a smallish fingerling?

A. Dig a shallow trench about 6-8 inches deep. This can be done with a rake in loose soil, but you may need a shovel or hoe in heavier soils.

Place cut potatoes 10-12 inches apart in the trench. If larger potatoes are planted whole they will produce larger plants and should be given a little extra room, 12-16 inches.

A spacing of 36 inches between rows in adequate but if you have the extra space, further spacing will make hilling easier.

Fingerling and other small potatoes can be planted closer, but no less than 8 inches between plants.  Cover the plants with about 3-4 inches of soil, leaving the trench partially filled.

Q. The hilling thing is probably the most confusing part (and the most work). When and how deep and often do I hill, and where is all that extra soil meant to come from? Can I use straw or composted leaf mold or some other “mulch”?

Potatoes hilled a second time, with straw
A. Hilling is the most crucial, tiring and fun part of growing potatoes.  When your potatoes reach about 8-10 inches high, bring soil up around the vines from both sides.  This can be done with a rake in loose soils. If your soil is hard, you may need to cultivate the soil before raking or use a hoe.

Make sure not to cultivate too closely to the young plants as to not disturb the new roots systems.  Hilling brings loose soil around the vines where the potatoes will form as well as deepening the roots into cooler soil.  With the first hilling, I like to cover the vines up so that only the top leaves are exposed.  This allows for a shallower second hilling done 2-3 weeks later with an additional 2-4 in of soil brought around the vines.

A mulch that is loose and allows the soil to breath can be applied after, or instead of, a second hilling.  I recommend straw [above photo, a second hilling of straw in Margaret’s garden] because it breathes well, but leaves can be used as long as they are not applied too thickly.

A good layer of mulch can help protect vines from potato beetles by creating a barrier as well as providing habitat for insects that eat the beetle’s larvae. The fun part of hilling is looking at your beautifully hilled rows when you are done!

Fresh-dug early red-skinned potatoesQ. What’s the above-ground signal for when it’s OK to harvest new potatoes? Do all varieties offer this possibility?

A. Potatoes begin to produce tubers after flowering.  Several weeks after flowering, dig into the loose soil at the sides of the vines and you shouldn’t have to dig deep to find thin-skinned new potatoes.  These can be pulled from the plant without harming the development of the still maturing potatoes.

The waxier-textured potatoes are best for immature use.  The variety ‘All Red’ makes for a colorful new potato with bright red skin and a pink streak through the flesh.  ‘Yukon Gold’ is another early maturing variety with great flavor.

Q. How do I know when the crop is done, and how long can I leave them safely in the ground after that?

A. Potatoes are ready to harvest when their vines die back and they lose most of their color.  This can occur with a frost or simply when they have reached full maturity.

I like to mow the vines a few weeks before harvest.  This helps toughen the skins for good storage.

Potatoes can be left in the ground for several frosts, but should be harvested before the danger of a heavy frost that could damage the spuds lying closest to the surface.

101 comments
April 4, 2013

comments

  1. Ruth Tomlin says

    Hi, I have potatoes growing and looking healthy, but couldn’t find enough spare soil to hill them, so today I scrunched up lots of newspapers, and piled them liberally around my potatoes, then covered it with a thick layer of mulched leaves from our pittosporum hedge and gave it some dynamic lifter, and a good water, so we will wait and see how the results turn out.
    Thank you for your website, I love to read it

    • margaret says

      You’re welcome, Ruth. You must be gardening somewhere warm! I usually use compost if I have it in the heap, or straw if not.

  2. Jim says

    I have red skin potatoes that I grew from unused store bought and under the skin there is a light brown. Can you tell me what’s up?

    • margaret says

      I don’t know if you mean spots of brown, and how deep, or brown over all, so start here, at Cornell’s potato diseases ID page. If you scroll down and then click on the blue links (names of diseases) it will reveal a grid of photos keys to each disease, like scab and scurf and ring rot and so on. Keep scrolling to see ALL the possibilities and if any look familiar.

      Potatoes from the market are not ideal for using as starts because they’re not certified as disease-free “seed” potato stock, which I prefer to start with each year.

    • margaret says

      Yes, Kevin, if the containers have lots of good drainage holes and are big enough–like closer to a whiskey barrel more than a small flowerpot or bucket size is better.

  3. Poulsbo Garden Lady says

    After good success using potato grow bags for several years, I thought last year that it would be fun to try the wire cage with straw and compost featured in Fine Gardening magazine last year for more potatoes with a surplus hopefully to donate to our local food bank. Long story short, I planted on St Pat’s day as in previous years (recommended in our PNW area) and was so disappointed. This year, I am planting later and will use the growbag and cage method to better evaluate what went wrong last year. I don’t grow in the ground because our soil can become quite soggy and my other raised beds are full of other cool season veggies.

  4. JENNIFER says

    I have a question about Yukon Gold species. I planted them last year and did exactly what you said but used the straw (not enough soil to hill). I only harvested potatoes from the soil…none from the straw. So I tried to research and one place said YG don’t hill… they only produce in the original soil. Is this true? I have new raised beds this year and would like to try it again. Should I “hill” them? Thanks for the help.

    • margaret says

      I don’t know, Jennifer, but it is a determinate variety with a fairly compact root system compared to other varieties, so perhaps that was the issue – the growth habit of the YG plant, not straw or no straw.

  5. Barbara says

    I have a question. I have a good many kennebec potatoes left from growing and buying some from farmers. They have not only sprouted, but the sprouts have grown so that they “reach out” when one enters the room! I’m in zone 6 and am wondering if I can plant these with the leggy sprouts upright and have a harvest? I brought some up from the basement for cooking last week and the sprouts of the ones I didn’t use turned green, just as if they were growing outside! Thanks for knowledgeable answers. :-)

    • margaret says

      Hard to say if they are prime condition for growing, or if they are too far gone (from not storing in ideal conditions are pushing their growing points too early). I like to start from fresh certified seed potatoes each year.

  6. says

    I planted some potatoes in X-Large “Potato Bags” last year but only managed to hill one bag before I got sick. This bag grew the Ozette Fingerlings, which tasted terrific. I’m growing them again this year, plus some Yellow Finn.

  7. Jean Horne says

    My yukon gold potatoes did not have any flowers last year. I didn’t make any taters. What would cause them not to flower?

    • margaret says

      Hi Jean. Too much Nitrogen will cause lush green plants but sometimes at the expense of flowering, for example; compost is the best soil-additive, not lots of fertilizer. Some potato varieties don’t flower, I have read, so I think it’s more whether they had a full season in the ground, with regular watering throughout, hilling, and etc. as above in the article.

      Did you let the vines die down completely on their own before harvest?

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