Potatoes are one of the staple plants of a spring garden, and there are many reasons to grow your own rather than supermarket stock. This year we will have 32 varieties in stock, far more than the two or three you can find at a supermarket!
Potatoes can be broken down into three growth types and two-three texture types, the growth types determine how quickly the plant grows and when potatoes should be harvested whilst the texture types help tell what the potato can be used for.
First Early potatoes are harvested early and are often used for boiled or salad potatoes, they are avoidant of blight as they are often harvested before it has made an appreciable appearance. They have an average time of harvest of 10 weeks although some may be left later to mature slightly giving them a stronger taste and sometimes shifting them more towards the floury scale. They are often smaller plants than other potatoes and can be planted closer together. Plant these potatoes in March
Second Early potatoes are planted at the same time as first early, in March but they mature for longer at about 13 weeks. They are often heavier croppers than First Earlies but not as heavy as main crops. These lean more towards the floury side of the scale and are often mid-range, although as always there are exceptions to the rule.
Main Crop potatoes are much more productive than the earlies however they also have a natural susceptibility to blight so should be looked after. These often are the most flavoursome potatoes with larger floury tubers that are ideal for baking. They can take up to 15 weeks to be ready for harvest. They ideally are planted in late March / April.
2nd Main Crop potatoes do exist, these are often planted late April and can take up to 20 weeks to mature however they are very prone to blighting and therefore are not often grown in this country. These often have very large tubers which are packed with flavour. Unfortunately as potatoes are not suited to grow in greenhouses (the warmth inhibits tuber growth) they can be very problematic in blight prone areas.
The texture of a potato is the most important thing to consider when cooking potatoes, If they are floury then they can be prone to breaking up when boiled (as they absorb water with ease) whilst if they are overly waxy they may be able to be boiled for hours on a low heat but they make poor roasts. The middle of this scale is called firm, where the potato has enough dry matter to make a good roast but dose not break up readily when boiled, making it a good general purpose workhorse.
Floury potatoes have a high dry matter content meaning they produce fantastic light roast, baked and mashed potatoes. This is both a benefit and a problem as the floury starch absorbs butter and milk with great aptitude however they also have a tendency to collapse when boiled as they absorb too much moisture.
Firm potatoes are a midway point between the waxy and floury potatoes, they are usefully for many purposes, as they provide more taste and a better texture as roasts than waxy but are more likely to withstand boiling than floury. They are ideal for chips and wedges.
Waxy potatoes tend to be early as they have not fully developed the starchiness of main crop potatoes however there are exceptions. A waxy potato often has a thin slightly translucent skin which is easy to rub off. These are ideal for boiling as either new potatoes or as salad potatoes. Some varieties can be boiled for hours, making them ideal for restaurants where there can be long waits between meals.
Potatoes are normally grown from seed potatoes from elevated North Scotland (as the main vector for diseases is the aphid which is entirely unsuited to the climate) However it is possible to use saved potatoes for planting and it is even possible to take stem cuttings from any misplaced potatoes from last year (as long as their still in good condition). To do this the potato must have started sprouting and often the tuber has started to whither. At this point then take the stems off the plant with a sharp knife (weak stems could do with a small chunk of potato as this is after all a food store) and are planted, stem point down into damp compost kept inside a house (ideally multipurpose as it is lighter and easier for new roots to develop in).
It is important to keep the soil lightly moist however never wet, the potatoes should quickly root within a few days if kept in a warm location. These potatoes can be planted out along with your early potatoes and will mature quickly, having had a head start therefore providing a tasty precursor to your later croppings.
Potatoes are among the easiest plants to grow, part of the reason they are so wide spread and popular among armature growers. There are several methods of how to grow them, however relevant to all of them are a few basics:
First and most importantly- Never use contaminated potatoes or potatoes thought to have been infected with disease, especially blight.
Secondly, potatoes grown in the light produce green skin which is poisonous (not deadly just unpleasant)
Thirdly, potatoes grown in overly warm conditions stop producing tubers, therefore potatoes grown in pots produce lower yields
Finally, potatoes should in most circumstances be 'earthed up' therefore promoting more growth and reducing the chance of green potatoes
Potatoes are one of the few vegetables that prefer a loose soil to a heavy and having an acidic soil is not only their preferred environment (5-5.5 pH) it also reduces greatly the likelihood of powdery scab. It is worth, especially if planting in soil to plant potatoes with a thick mulch of grass clippings as these will acidify and lighten the soil whilst providing a good dose of nitrogen as they break down. With potatoes avoid over-watering until tubers start to form as this will promote a lot of foliage growth at the expense of the tubers. After they have started to form however. water as much as you want.
Chitting is the act of causing the potato to sprout before being planted in the soil, this effectively gives the potato a head start as it is already active when planted. The normal method is to place a potato in an egg container and keep it in a warm, light position, in addition this can turn the skin of the potato green as it produces unpalatable toxins which 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. By cutting a potato, as long as it has at least one active eye you can replicate it as a vegetative clone. It is however best if the section is bigger than a golf ball or ping-pong ball and to ensure it produces a strong plant, 2-3 eyes should be active or sprouting. When the potato is split then it is best not to plant it immediately as if left to dry it will seal itself and therefore it is more resistant to infections attempting to attack the wound. Do not worry if it appears to go black or shrivel slightly that's normal!
The 'Traditional Method' is still the most practised today as it is well proven 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.
You can plant the potatoes in raised beds (high yield), trenches (ideally mulched with grass cuttings), raised mounds (ideal in clay gardens or to reduce work) or raised rows (Ideal for allotments). after they have been planted, in whatever form they should be covered over with ~10cm of soil. The traditional way to do this has been to simply rake soil from the surrounding area, thus providing drainage and smothering weeds however in heavy soils then a light compost may be better. This should be done regularly as soon as the potato tip appears. After 4-5 earthlings then allow the potato to grow, keeping it watered as tubers start to grow. 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|
The 'Pot Method' has its own advantages but also some rather serious disadvantages, this 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. The main problem with using pots is the reduced yield. There are many reasons for this, such as the pot warming up faster (warm potatoes do not produce as high yields) water problems (it is easier to underwater potatoes) and often a poor soil structure all culminating in low yield and plant stress (which primes the plant for blight).
However there are redeeming facets to the Pot Method, in that it isolates the potatoes from the ground, and therefore offers protection from the many problems that may befall them. In addition it is easier to acidify small amounts of soil than an entire garden plot. If organisms such as nematodes which destroy tubers are present in the soil beds it can be impossible to plant for several years.
The same principles about earthing up apply from the traditional method, the higher you earth up the potato, the more productive it is. Rather however than planting a single potato it would be worth planting 3-4 potatoes in an attempt 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 organic gardening's view on soil and the use of large amounts of mulch rather than digging. This method is entirely different to the previous options and is gaining in popularity. If you have a problem with potato eelworm, weeds or have a bad back I would highly recommend attempting No Dig growing. This should be done slightly later than normal as plants are more vulnerable to frost.
|Potatoes are very clean and easy to harvest||Slightly lower yield due to warmth|
|Very little work is needed to harvest||No fork damage to potatoes|
|Kills most weeds||Requires more watering|
|No fork damage to potatoes||Potentially hides rodents that may attack crop|
|Mulch feeds the garden||Potentially more vulnerable to frost damage|
|Uses any excess grass clippings|
|Very few Volunteer potatoes|
|No earthing up|
|Reduces damage from potato eelworm|
|Loose soil is ideal for potatoes|
Initially the ground should be hoed (Traditionally this is avoided as it causes weed germination) to a fine tilth, If the soil is particularly heavy then adding a 1" well rotted / composted manure mulch would be beneficial however it is only needed on heavy clay. Ensure the ground is watered as this is one of the largest potential problems. Plant the potatoes apart as in the traditional method in rows with distances the same as in the traditional method. Next cover in a mulch of straw 5-6" deep and to keep the straw stable it is ideal to use a light cover such as fleece or wire mesh. Hay can be used however it is finer meaning it is more prone to flying and it tends to carry seeds. Again water the straw and leave until the plants start to poke through.
When plants are visible then it is best to remove the restraining material and then re-mulch with grass clippings. These are heavier and are less likely to be blown around whilst providing a mulch and source of nitrogen. The mulch should not be packed tight as that may cause too much heat to accumulate and reduce yields. Treat as normal potatoes (although the plants must be kept well watered). Shredded paper is also very useful as it breaks up into a high nitrogen feed. At harvest time then you can check the size of potatoes easily by reaching through the mulch and may even harvest some without destroying the entire plant.
Potatoes are an easy plant to physically harvest however the timing can be complicated some times, All of the potato groups have a different time to harvest but that can change with the weather and the growth of the potatoes. If they are planted in a light soil it is sometimes possible to feel the size of the potatoes but the following times can be used as a rough guide.
|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 down and wait 10 days)|
Whist with earlies and salad potatoes you generally eat when harvested, Main crop potatoes are best left for 10 days underground after the haulm (potato foliage) has been cut down to 1". This has the effect of hardening skin and making them suitable for storage. After lifting them then it is ideal to 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 allow some airflow.
Potato Blight is the big problem with potatoes, it is prominent in the late summer, mostly affecting main crop potatoes and is the same disease that caused the Irish potato famine. It is activated by what is called a Smith Period where the minimum air temperature is above 10* and humidity is above 90% for a minimum of 11 hours each day in a 2 day period, In some cases a near miss is possible such as a 87% humidity. It is possible to check this through the Met office or use of the Blightwatch site which can predict blight reliably within a post code area.
Blight is characterised by a rapid blackening of leaves and stem sections in a watery black rot at which point the tubers are infected and rot in the soil. Late Blight the most common form of this in the UK and also infects tomatoes. Whilst a fungicide such as Bordeaux mixture or other copper based fungicides give a control of blight and hot dry weather arrests greatly weakens symptoms and spread, once it has occurred it is impossible to stop. Whilst tomatoes can often be harvested it is advised to immediately destroy potato plants and tubers. If you have had blight be very wary about planting previously infected potatoes. it is better to incur the cost of new seed potatoes than to contaminate a new crop.
Blight overwinters only on living tissue, this normally means volunteer potatoes. 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 chopped or shredded (possibly with a lawnmower) to speed degradation.
Spores are wind spread and therefore growing crops in a glasshouse or under protection will significantly reduce disease penetration.
Copper fungicides can be used as a preventative measure however are unable to cure an infection that has already been established.
When 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 controls: Copper based products interfere with the germination of spores and therefore only work before the disease is established.
Bordeaux Mixture and Bayer Garden fruit and vegetable disease control.
Cultural Control: Removing excess leaves reduces the humidity around a plant and increasing air flow reduces temperature and humidity which are needed for blight to establish. After blight has settled on the plant then cutting the haulm down and waiting 10 days stops it penetrating the tubers. Remove all volunteer potatoes and never replant from infected stock.
Recently there is a new family of potatoes developed from the Sarpó strain, they have coloured skin and great resistance to tuber blight with good resistance to leaf blight. The downside is they are all extremely floury and can be difficult to cook without breaking apart, so are best used for roasting and chipping.
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.
Control: As scab only occurs in alkaline soil (which potatoes are ill suited to and ideally should not be planted in) the best methods of prevention are to avoid limeing the soil before planting, add grass clippings to the soil / trench and to water when dry. There is no need for a (and no suitable) chemical control.
Swollen Lenticells are normally found on potatoes that are planted in very heavy soil or over watered. The lenticells are respiration points that get clogged (imagine a spot) and therefore form white mould like protuberances. These can simply be rubbed off and they cause no taste difference or damage to the potato although it dose potentially reduce storage life.
Control: Planting potatoes in a light soil is not only beneficial for them but it reduces the chance of this disorder affecting them.
Potato Cyst Eelworm
There are two forms of eelworm, Golden and White. It is hard to distinguish the two without seeing the colour of the cysts (as the name suggests they are distinguishable) however nearer autumn the cysts all brown. After infection the nematodes 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, if there is a heavy attack it can entirely decimate and kill the crop of potatoes.
Symptoms of Eelworm include dieback of potatoes, weak growth, low cropping 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 however dose 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|
Control: Crop rotation will reduce impact however this includes most of the solanum family. Infected plants should immediately be destroyed, the roots taken out and ideally burned. Nematocides are not recommended. Use of the No-Dig method reduces the impact of this pest and first earlies are normally harvested before this becomes a significant issue.
It is my belief that like onion white rot, because eelworm are dormant until they detect a potato tuber in active growth that they can be artificially stimulated and therefore break the life cycle. This would be best accomplished by chitting potatoes and then possibly mincing or grinding the potato and then applying it to the ground (potentially after soaking in water to release more chemicals. If anyone has a problem with eelworm and would like to test this then please feel free to contact us at the shop.
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 prone to rot in storage.
Control: Plant in well drained areas, waterlogged soils are far more problematic. Planting resistant cultivars such as Kestrel and Cara whilst avoiding Estima, Maris Bard and Wilja. Lift crops in dry weather and allow to dry before storage. With main crop plants leave the tubers in the ground for 10 days after removing the haulm.