Tuesday, August 19, 2014

Growing Potatoes


Much has been written about growing potatoes (methods, varieties and so on), but some of the basic facts about potatoes do in my opinion not get enough attention.  In this blog post I will focus on them, because then everything else falls into place.

How potatoes grow

A good starting point is a photo I took early in the season after carefully digging out a potato plant:

This photo shows the original 'seed potato', the one put in the ground by me, and what happened after that.  The seed potato has grown in size (the seed potatoes you buy are small).  It has formed a stem and foliage above ground (not in the photo) and is now beginning to form new potatoes.  The really important information that can be taken from this photo is that all the new potatoes are above the original seed potato.  This is not just the case with this particular plant in this particular photo.  Potato plants form new potatoes only above the original potato the plant started with.

Last season I put a new raised bed on top of an existing garden bed. This year potatoes are coming up in the raised bed from down in the original soil below the bed. I did not want them in that spot, so dug them out and this is what I got. The stalks are 30 cms long, so if you plant spuds that deep below the surface, they will come up. That is good to know because new spuds always grow above the seed potato you planted. Planting spuds deep means you don't have to hill so much later on to get a good crop.  
 

What potatoes need

Here is a photo of seed potatoes ready to be covered with soil:


Each potato row is around 15 cm down from the top of the hill that is parallel to it.  I am not going to use the soil from the hill to cover the potatoes.  I am going to take totally composted compost from my compost heap and cover the potatoes with that.  The hills will stay as they are at present and I will fill the trenches with soil, compost, mulch, whatever material I have, so the potatoes will be 15 cm deep underground.  That gives my potatoes 15 centimetres of space to form new potatoes in AND it puts me 15 centimetres ahead of potatoes planted at ground level, using the 'no-dig method'.

Potatoes, just like all other annual vegetables, should not be planted in the same spot every year.  I know that some Tasmanian potato growers grow their potatoes in the same place every year and sooner or later this will lead to crop failure or disease or both.  My guess is that questionable non-organic practices allow them to get away with it.  Their crops will not be nutrient-rich.  If you like to know more about crop rotation and where potatoes fit in a good rotation system (not hard) click here for a Food Garden Group blog post on this issue.

What kind of soil do potatoes like best?  I have heard it said that 'they grow Pink Eye potatoes in the dunes at South Arm, so they can't need much'.  The potatoes grown in that area are grown on slopes (good drainage) up-hill from the dunes, in fine loam, not in sand.

Potatoes need good slightly acid soil (pH 6 - 6.5) that is well-draining and not too nutrient-rich.  If grown in nutrient-rich soil they grow, but the foliage becomes spectacular (a metre high or more ; I have had this ; very impressive), with all the energy taken up with forming leaves and little used to form potatoes.  A potato crop grown in soil that is too rich can be a real disappointment.  Once again, it is good to fit potatoes in a crop rotation system, so they don't follow your legumes or are planted straight after fertilising your soil.

Chitting

Chitting is the term used for allowing potatoes to sprout by putting them in a cool but light spot.  Chitting is not essential for success.  Potatoes will sprout if you plant them without hitting them first, but if potatoes already have small sprouts they have a head-start when put in soil.

The 'no-dig' method

I know that growing potatoes using the no-dig method is popular and I understand why: it is less work and you do not disturb the soil.  It is less work because you just make your soil weed-free, then lay your potatoes in rows and cover them with soil, compost and mulch.  Not disturbing the soil is also a plus, because it means that worms, microbes and so on continue their activity rather than being disturbed or worse, being killed.  However by planting at ground level it is very likely that your crop will not be large because you will need a really large amount of soil, compost and mulch to create the space above the seed potatoes where new potatoes will form and most home-gardeners will not have enough material to create a 15 centimetre or higher layer above ground.

No matter how you grow potatoes, the problem is that any potato that is exposed to the air will go green.  Green potatoes are poisonous and should not be eaten.  So during the potato growing season it is always a challenge to stay ahead of your potato plants and add so much soil, compost and mulch around your potato foliage so that no newly forming potato ever sees the light.  Not an easy task if you only have limited amounts of soil, compost and mulch.  Growing potatoes using the 'no-dig method' is fine, but it makes this task so much harder.  If you like to try the no-dig method consider putting a frame that is around 30 centimetres high around your potato patch, so when you fill it up with soil your potato patch becomes a raised bed.

I dig 15 centimetre deep trenches.  I realise I disturb the soil when I do, but I am reconciled with this because I use a four-year crop-rotation system and therefore disturb every patch in my veggie garden just once every four years.

Potato varieties

There are early and late potato varieties, some varieties store well, others don't and are best eaten fresh. Some varieties are 'all-rounders', some are 'waxy' and others are 'floury'. The differences between the many varieties is bewildering.

A Guide to Potato Varieties on this blog may help you choose a variety that suits your needs.

Growing potatoes in containers

Potatoes are a cool-climate crop.  This is why in Australia the best potatoes are grown in Tasmania.  In South America, where they come from, they don't grow in warm areas.  They grow higher up in the mountains.

What does that mean for growing potatoes in containers ('grow bags' or pots)?  Growing potatoes above ground-level in pots or bags is possible if you are able to keep the new potatoes that form out of the light (non-transparent bag or pot) and cool.  Your plants may literally cook on a hot day in the sun.  Some people use containers on wheels and move them in and out of the sun as required.  Making sure the soil is always moist, but not wet, is also crucial.  You will need to plant your seed potatoes deep and add soil as the season progresses.

All three methods of growing potatoes (underground, no-dig and container) can work if you realise what potatoes need and make sure they get it.

When to plant

Potato leaves go black if affected by frost (and plants may die), so, if you have frosts in your garden, plant potatoes once the chance of frost is low.  Mulching young leaf growth with for instance straw can help prevent frost burn.

By planting potatoes as early as possible you give plants the longest possible growing season.  I plant mine 15 - 20 centimetres deep, with 30 centimetres between plants and rows, but that is because I don't have a lot of space.  If you have a big garden put 50 centimetres between rows.

In theory you could use some of your own last-season potatoes as seed potatoes for your next crop if you did not have any diseases.  However, most people buy certified seed potatoes because they are guaranteed disease free and not expensive.  Best moment to plant is when they begin to sprout.  Don't be alarmed if nothing comes up for a while.  Potatoes planted 15 centimetres deep will take 3 to 4 weeks to reach the surface.

What to do next?

After planting tubers begin to form stems and leaves.  Don't be impatient.  It may take a few weeks for anything to appear above ground if you plant your potatoes deeply.

When they appear above ground you can spray them with liquid seaweed once a month, but in most cases this is not necessary.

Flowers will begin to form around 3 - 4 months later.

At this stage most new potatoes will be formed and this is a crucial time to hill your plants, i.e. add as much soil, compost, mulch, whatever you have, around each plant.  You can take some of this from between the rows, but tubers can form some way away from plants, so don't scrape away too much.

Keep the soil moist, but not wet.

In Tasmania you don't have to worry too much about potato diseases if you started with certified seed potatoes, your soil is well-drained and your soil does not contain an excess of lime.

When can potatoes be harvested?

Many people 'bandicoot' potatoes in January or even earlier.  They carefully dig and take one potato from each plant, leaving the plant intact.  Officially potatoes are ready for harvest when the foliage has died off.  That is likely to be in March, but you can leave them in the ground for a few more months until you need them.

Given the right conditions a small potato plot can yield a lot of potatoes:

After years of not very spectacular crops and learning along the way, this is what this year came out of just 3/4 square metres of my garden.  Not all potato varieties are equally productive.  The variety above is Dutch Cream.

This year my potato patch yield was four of these buckets, so I am now experimenting with storage methods.  In a cool dark place under our house I put two very large laundry baskets.  After digging up the potatoes, they were left to dry for a few hours, then, without too much cleaning, they were put in laundry baskets in layers, with newspaper in between (see below).  I covered the baskets with blankets and the area they are in is dark and cool.

I am told that I should check each layer fortnightly and remove shoots.  This apparently prevents stored potatoes from going wrinkly.  I will let you know how effective this method turns out to be.


2 comments:

  1. hello! i've just found your blog - it's great to find a local gardening site! i can't wait to read thru your previous posts, there looks like lots of great advice (i've just printed out your calendar of gardenings chores/things to plant) so i'm really inspired by your local knowledge.

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    1. Thank you for your comments. Did you realise that this is more than a blog? We are a group that meets in someone's garden once a month and we also have a Facebook page. Please let me know if you like to join.

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