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GROW GUIDE - POTATOES

Updated: Mar 7

Potatoes are a staple of the spring garden, and there are many reasons to grow your own rather than heading to your local supermarket. This year we will have 32 varieties in stock, far more than the two or three you can find at a supermarket!


Different types of Potato

Potatoes can be broken down into different growth and texture types. The growth types determine how quickly the plant grows and when potatoes should be harvested, and the texture types suggest what the potato can be used for.

First Early potatoes should be planted in March and harvested at approximately 10 weeks. This makes them avoidant of blight as they are often harvested before it can make an appearance. Some First Early potatoes may be left to mature, which gives them a stronger taste and a more floury texture. There mature plants are often smaller and can be planted closer together. First Early potatoes are best served boiled or in salads.

Second Early potatoes are planted at the same time as first early, in March, but they mature for longer and are harvested at 13 weeks. They often produce more crop than First Earlies, but not as heavy as main crops. Usually these are more floury and mid-range than First Early potatoes.

Main Crop potatoes are much more productive than the earlies, however they also have a natural susceptibility to blight as they can take up to 15 weeks to be ready for harvest. These often are the most flavoursome potatoes that are ideal for baking. This variety should be planted in late March/April.

2nd Main Crop are often planted late April and can take up to 20 weeks to mature, meaning they are prone to blighting and not often grown in this country. However, they do produce large tubers which are packed with flavour.

When cooking potatoes you should take into account its texture. A floury potato will break up when boiled but make an excellent roast, whereas a waxy potato will boil nicely but make a poor roast. In the middle of this scale are firm potatoes, where the potato has enough dry matter to make a good roast but does not break up readily when boiled, making it a good general purpose workhorse.

Floury potatoes have a high 'dry matter' content, meaning they produce an excellent roasted, baked, or mashed potato. The floury starch absorbs butter and milk nicely, however they do have a tendency to collapse when boiled due to absorbing too much moisture.

Firm potatoes are a midway point between the waxy and floury potatoes. They provide more taste and a better texture for roasts than the waxy variety, but are more likely to withstand boiling than floury. They are ideal for chips and wedges.

Waxy potatoes tend to be Early Crops and do not develop the starchiness of Main Crop potatoes. A waxy potato often has a thin slightly translucent skin which is easy to rub off and are ideal for boiling as new or salad potatoes.


How to Grow

Potatoes are among the easiest plants to grow, part of the reason they are so wide spread and popular among amateur gardeners. Some basics everyone should know are:

  • Never use contaminated potatoes or potatoes thought to have been infected with disease, especially blight.

  • Potatoes grown in light conditions produce green skin which is poisonous (not deadly, but still unpleasant).

  • Potatoes grown in overly warm conditions will stop producing tubers, therefore potatoes grown in pots produce lower yields.

  • Finally, potatoes should, in most circumstances, be 'earthed up' which promotes more growth and reduces the chance of green potatoes.

Potatoes are one of the few vegetables that prefer a loose and acidic soil (5-5.5 pH). To increase the acidity of soil you can plant your potatoes with a thick mulch of grass clippings, which will increase the acidity and provide a good source of nitrogen as it breaks down. Avoid over-watering your plant until the tubers begin to form, but once they start to appear you may water them regularly.


Chitting

Chitting is the act of making the potato sprout before being planted in the soil, this effectively gives the potato a head start as it is already active when planted. The usual method is to place a potato in an egg container and keep it in a warm, light position. One particular benefit of this method is that exposing the potato to light can turn the skin green, which may stop animals attempting to dig and eat it. This method is best used with earlies but can also be useful with main-crop potatoes.

It is also possible to divide potatoes if they are large enough. As long as each piece has at least one active eye you can replicate it as a vegetative clone, although it should be noted that this works best if the sections are larger than a golf ball and have 2-3 active or sprouting eyes. Avoid planting your split potato immediately. Give it time to dry and seal itself which will make it more resistant to infections attempting to attack the wound. Don't worry if it appears to go black or shrivel slightly - that's normal!


Traditional Method

The 'Traditional Method' is still the most common today - it is well established and provides greater yields with less care than either the pot or no dig method. This method focuses around the initial planting and a constant earthing up (either with soil or mulch) to effectively extend the tuber producing underground stem of the potato and to minimise green skins.

Plant the potatoes in raised beds (for a high yield), trenches (mulched with grass cuttings), raised mounds (ideal in clay gardens) or raised rows (ideal for allotments). After they have been planted they should be covered over with approximately10cm of soil. Simply rake soil from the surrounding area, thus providing drainage and smothering weeds, however if your soil is particularly heavy, a light compost may be better. This should be done regularly as soon as the potato tip appears. After 4-5 earthings allow the potato to grow, watering as you see tubers appear. With potato mounds, it is possible if they are large enough to check and harvest some of the more mature potatoes without destroying the plant.

Potato Type

Distance (by plant, by row)

1st early

12" between plant - 24" between rows

2nd early

15" between plant - 30" between rows

Main crop

18" between plant - 30" between rows

Pot Method

The 'Pot Method' is best suited to those with limited growing space or people growing first/second earlies. As the name suggests, the pot method involves the use of containers rather than ground planting. A disadvantage of using pots is the reduced yield - there are many reasons for this, such as; the pot warming the soil (warm potatoes do not produce such high yields), water problems (it is easier to underwater potted potatoes), and poor soil structure. This may also cause the plant stress which makes it more susceptible to blight.

There are benefits to the Pot Method. Growing the plant away from the ground quarantines them from diseases and pests that may destroy the crop. If organisms, such as nematodes, are present in the soil beds it can be impossible to plant for several years. Additionally, it is easier to acidify small amounts of soil than an entire garden plot.

The principles of earthing up still apply with the pot method. The higher you earth up the potato, the more productive it is. Rather than planting a single potato it is recommended to plant 3-4 potatoes to maximise production. Potato growbags are available which are useful to collapse and store throughout the winter.


No Dig Method

The No Dig method is derived from the principles of organic gardening and the use of large of mulch as opposed to digging. This method is entirely different to the previous options and is gaining in popularity. It is particularly good for those suffering with a bad back! Tip: If using the no-dig method, start slightly later than usual as your plants will be more vulnerable to frost.



Advantages

Disadvantages

Potatoes are very clean and easy to harvest

Lower yield due to warmth

Very little work is needed to harvest

Requires more watering

Kills most weeds

Hides rodents that will attack crops

No fork damage to potatoes

Potentially more vulnerable to frost damage

Mulch feeds the garden

Uses any excess grass clippings

Very few volunteer (or 'left behind') potatoes

No earthing up

Reduces damage from potato eelworm

Loose soil is ideal for potatoes

Initially, the ground should be hoed (this is avoided in other methods as it causes weeds to grow) to a fine tilth. If the soil is a heavy clay then add a 1" well rotted / composted manure mulch. Ensure the ground is watered and plant the potatoes apart and distanced, as in the traditional method. Next, cover in a mulch of straw 5-6" deep and, to keep the straw in place, use a light cover such as fleece or wire mesh (hay can also be used, but it is finer and more prone to being dislodged and spreading seeds). Water the straw and leave alone until the plants start to poke through.

When plants are visible remove the restraining material and then re-mulch with grass clippings; these are heavier and a good source of nitrogen (shredded paper will also work well, although it is lighter). The mulch should not be packed tight as this may cause too much heat to accumulate and reduce yields. Treat your potatoes as you would with the previous methods, although be sure they are well watered. Before harvesting, you can check the size of your potatoes easily by feeling through the mulch, and can harvest them without destroying the entire plant.


How to Harvest

Potatoes are an easy plant to harvest, but the timing can be tricky. All of the potato groups have a different harvesting period, but this can change with the weather and the growth of the potatoes. The table below gives a rough guide to optimum harvesting times.


Harvesting Type

Harvesting Time

1st Earlies

10 weeks, or when flower buds appear

2nd Earlies

13 weeks, or when flowers are in bloom

Main Crop

15-20 weeks when foliage yellows (cut plant and wait 10 days)

Earlies and salad potatoes can be eaten right after harvesting, but it is better to leave Main Crop potatoes for another 10 days underground after cutting the potato foliage (haulm) to 1". This allows time for the skin to harden them and make them easier to store. After lifting them, allow them to dry for a few hours and then bring them inside. These potatoes should last a significant amount of time in a cool dark place but be sure to allow some airflow.


POTATO PROBLEMS


Potato Blight

Blight (the disease responsible for the potato famine) is a big problem for potatoes. It is prominent in the late summer, mostly affecting main crop potatoes. It is activated by a 'Smith Period' where the air temperature is above 10 degrees Celsius, and humidity is above 90% for a minimum of 11 hours each day, in a 2 day period. The Met office or the Blightwatch site can help you predict the risk of blight within a postcode area.

Blight is characterised by a rapid blackening of leaves and stem sections with a watery black rot, at which point the tubers are infected and rot in the soil. Late Blight is the most common form of this in the UK and can also infect tomatoes. Unfortunately, once it has occurred it is impossible to stop Blight, although copper based fungicides like a Bordeaux mixture can prevent blight outbreaks. Whilst tomatoes can often be harvested, potato plants and tubers with blight should be destroyed immediately, and it is best to plant entirely new seed potatoes to avoid contaminating a new crop with previously infected plants.

Control:

Blight overwinters only on living tissue, this normally means volunteer potatoes (potatoes that were missed during harvest and remain in the ground). If blight has appeared in your garden have a thorough search for any potatoes still in the ground and remove them. Infected tissue can be composted however it should be well chopped or shredded to speed degradation.

Spores are wind spread and therefore growing crops in a glasshouse or under protection will significantly reduce the chance of disease.

Copper fungicides can be used as a preventative measure, however they are unable to cure an infection that has already been established.

Once infection has set in, it is best to remove the haulm and to leave the tubers in the ground for 10 days before harvesting. Whilst this may mean a reduced yield it also reduces the risk of entire crop failure. Be especially vigilant for the removal of volunteer potatoes.

Chemical Control: Copper based products interfere with the germination of spores and therefore only work before the disease is established.

We recommend Bordeaux Mixture and Bayer Garden Fruit & Vegetable Disease Control.

Cultural Control: Removing excess leaves reduces the humidity around a plant and increasing air flow reduces the temperature and humidity which are blight needs to thrive. After blight has settled on the plant, cutting the haulm down and waiting 10 days stops it penetrating the tubers. Remove all volunteer potatoes and never replant from infected stock.

There is a new family of potatoes, developed from the Sarpó strain, that have a good resistance to tuber and leaf blight. These potatoes are, however, a floury variety and are best used for roasting and chipping rather than boiling.

Common Scab

Common Scab is a relatively harmless disease that is prevalent in alkaline soils. Whilst it may make the surface of the tuber look unappetizing it is no more dangerous than minor dermatitis on a human, and can be peeled off with a potato peeler (Note: please don't try this with humans, you will most likely be arrested).

Control: As scab only occurs in alkaline soil (which potatoes dislike and should not be planted in), the best methods of prevention are; avoid liming the soil before planting, add grass clippings to the soil / trench, and to water when dry. There is no suitable chemical control.

Swollen Lenticels:

A lenticel is a respiration point (like a pore) that can get clogged, and form a white mould. Swollen lenticels are normally found on potatoes that are planted in very heavy soil or over watered. They can simply be rubbed off and cause no taste difference or damage to the potato, although it can reduce storage life.

Control: Plant potatoes in a light soil.

Potato Cyst Eelworm

There are two forms of eelworm, Golden and White. After infection, they can persist in the soil for as long as 20 years and will attack any solanum, including tomatoes, in the area. Whilst potatoes can largely ignore a low infestation, a heavy attack can entirely ruin a crop.

Symptoms of Eelworm include dieback (where the plant begins to die from the tip of its leaf or roots, moving inwards), weak growth, poor crops, and coloured cysts on the roots.

The best control of eelworm is to avoid planting potatoes in infected areas and to rotate the crop you have grown there. This keeps infestations low, but does not control them. Some potatoes have a resistance to the Eelworms, however only a few have resistance to both forms.


Resistant to Golden

Resistant to White

Pentland Javelin

Cara

Maris Piper

Nadine

Nicola

Kestrel

Kestrel

Sante

Sante

Control: Crop rotation will reduce the impact of Eelworm. Infected plants should immediately be destroyed, the roots taken out and ideally burned. Nematocides are not recommended. The No-Dig method can minimise the impact of this pest, and first earlies are normally harvested before they can become a significant issue.

Potato Blackleg

Potato Blackleg is a common disease found mainly when the weather is particularly damp. Leaves turn pale yellow and stems blacken from 10cm above the soil to the roots. With mild attacks the tubers harvested can be eaten, however they are more likely to rot in storage.

Control: Plant in well drained areas, waterlogged soils are likely to encourage blackleg. Cultivators such as Kestrel and Cara are resistant, whilst Estima, Maris Bard, and Wilja are particularly susceptible. Lift crops in dry weather and allow to dry before storage. Main crop tubers should be left in the ground for 10 days after removing the haulm.


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