International Kidney Potatoes: A Late Variety

The breed of International Kidney potatoes is a popular choice among farmers and home gardeners alike due to its versatile nature, robust growth habits, and delicious, buttery flavor. Known for its distinctive characteristics, it is most famously associated with the “Jersey Royal,” a Protected Designation of Origin (PDO) potato from the Channel Island of Jersey. In this detailed guide, we’ll explore everything you need to know about International Kidney potatoes, from their plant characteristics to how best to grow and use them.

Whether you’re cultivating International Kidney potatoes on a large farm or in your backyard garden, this blog will provide you with all the insights you need to make the most of this unique variety.

Table of Contents

Plant Characteristics of International Kidney Potatoes

Maturity: Intermediate to Late

International Kidney potatoes typically mature from intermediate to late. This means that they require a longer growing season compared to some early potato varieties. The average growing period ranges from 100 to 120 days, making it important to plant them in the early spring for an optimal harvest in the summer. Their long growing season contributes to their rich, distinctive flavor.

Growth Habit: Spreading

The growth habit of International Kidney potatoes is spreading, which means the plant expands outward and covers a wide area as it grows. This characteristic is vital for gardeners to consider when planning their garden space, as these plants will need ample room to spread out and develop fully.

Foliage Cover: Moderate to Good

International Kidney potatoes have moderate to good foliage cover, which helps protect the potatoes from excessive sunlight and other environmental factors. The leafy green foliage also provides some level of protection against soil erosion and moisture loss, making it a resilient plant in the right conditions.

Flower Characteristics

Flower Color: White

The flowers of International Kidney potatoes are white, a common characteristic among many potato varieties. However, their flower frequency is rare, meaning you may not see many flowers blooming on these plants. This trait has little effect on the tuber quality but is an interesting point for gardeners who enjoy observing the full life cycle of their plants.

Berries: Very Rare

Following the rare flowering, the production of berries on International Kidney plants is even more infrequent. The occurrence of berries is classified as very rare, making this potato variety primarily valued for its tubers rather than any potential seed production via berries.

Light Sprout Color: Blue

One of the unique features of the International Kidney potato is its light sprout color, which is a striking blue. This can be useful for distinguishing the International Kidney variety from others when the potatoes are in their sprouting phase.

Growing Conditions and Tips for International Kidney Potatoes

Ideal Climate and Soil

International Kidney potatoes thrive in well-drained, loamy soil rich in organic matter. They prefer cooler climates, perfect for temperate regions with mild summers. If you’re planting in warmer areas, provide enough water during dry spells, as these potatoes can be sensitive to drought conditions.

Planting

When planting International Kidney potatoes, ensure the soil is prepared by turning it over and enriching it with compost or well-rotted manure. Plant the seed potatoes 10-15 cm deep, with each tuber spaced about 30 cm apart, and rows spaced 60 cm apart to accommodate their spreading growth habit. The blue-sprouted seed potatoes will begin to establish their roots and shoots in early spring, ideally in March or April.

Watering and Maintenance

Regular watering is key for International Kidney potatoes, especially during dry periods. However, be careful not to overwater, as soggy soil can lead to rot and other diseases. Mulching the soil can help retain moisture and prevent weeds from competing with your potato plants. Given their moderate to good foliage cover, International Kidney potatoes don’t need excessive maintenance, but it’s important to keep an eye out for pests like aphids and potato blight, especially as the plants mature.

Culinary Uses of International Kidney Potatoes

International Kidney potatoes are prized for their firm texture and buttery flavor, making them a fantastic choice for a variety of dishes. They are often boiled or steamed to retain their delicate flavor, but they also roast well. Their creamy, waxy texture makes them ideal for potato salads and holds their shape well when cooked.

Nutritional Value

These potatoes are not only delicious but also packed with nutrients. International Kidney potatoes are rich in complex carbohydrates, dietary fiber, vitamin C, and potassium, making them a healthy addition to any diet. Their relatively low-calorie content makes them a great option for health-conscious individuals.

Tuber Characteristics of International Kidney Potatoes

The International Kidney potato is known for its distinct tuber characteristics, which play a key role in its popularity among chefs and home cooks. These characteristics influence the potato’s appearance and its texture, flavor, and versatility in cooking. Let’s dive into the specific tuber traits of the International Kidney potato:

Tuber Skin Color: White to Yellow

The skin color of International Kidney potatoes ranges from white to yellow, giving them an appealing, light appearance. This pale skin color is one of the key identifiers of the variety, setting it apart from other potatoes that may have red or darker skin. The color can also become slightly more yellow depending on the soil and growing conditions, adding a subtle golden hue to the skin.

Tuber Eye Color: Yellow

The tuber eye color of International Kidney potatoes is a yellow shade, which blends well with the overall skin color. The eye color is not only aesthetically pleasing but also indicative of the potato’s maturity and readiness for harvest. The yellow eyes are easy to spot during planting and harvesting, helping distinguish the International Kidney variety from others.

Primary Tuber Flesh Color: Cream

The flesh of International Kidney potatoes is a delicate cream color, contributing to its renowned buttery flavor and smooth texture. This creamy flesh is perfect for a wide range of culinary uses, particularly in dishes where the potato’s soft, rich flavor can shine through, such as boiled or steamed preparations.

Tuber Shape: Long to Oval

International Kidney potatoes typically have a long to oval shape, giving them a more elongated appearance compared to rounder potato varieties. This shape makes them ideal for slicing and dicing in the kitchen, whether you’re roasting them, making wedges, or preparing them for salads. Their shape also allows them to cook evenly, making them versatile for different cooking techniques.

Tuber Eye Depth: Shallow to Very Shallow

One of the most convenient features of International Kidney potatoes is their shallow to very shallow tuber eyes. Shallow eyes mean there is less waste when peeling the potatoes, as the eyes don’t extend deep into the flesh. This feature makes them easy to prepare for both home cooks and commercial kitchens, where efficiency and minimal waste are important.

Tuber Skin Texture: Smooth

The skin texture of International Kidney potatoes is remarkably smooth, which adds to their overall appeal. Smooth-skinned potatoes are easier to clean and peel, making them more convenient for cooking. The smooth skin also gives them a polished appearance, making them particularly attractive when used in dishes where the skin is left on, such as roasted or boiled preparations.

Tubering Characteristics of International Kidney Potatoes

The tubering characteristics of International Kidney potatoes are another reason why this variety is favored by both farmers and home gardeners. These traits contribute to the overall productivity, quality, and storage potential of the crop, making it a reliable choice for growers. Let’s explore the key tubering characteristics of International Kidney potatoes:

Yield Potential: Medium to High

The yield potential of International Kidney potatoes ranges from medium to high, meaning that with proper care and optimal growing conditions, this variety can produce a substantial harvest. This characteristic is particularly important for commercial growers looking for a high return on their crop, but also for home gardeners seeking a generous supply of potatoes from their planting efforts.

While not the absolute highest-yielding variety, International Kidney potatoes balance quality and quantity well, offering a good harvest of premium tubers.

Tuber Size: Medium

The tuber size of International Kidney potatoes is generally medium, making them versatile for a range of culinary uses. Medium-sized potatoes are ideal for boiling, roasting, and baking, and they cook evenly compared to larger or smaller varieties. Their size makes them perfect for both home kitchens and restaurants, where consistency in cooking time and portion size is essential.

Tuber Shape Uniformity: Uniform

One of the standout features of International Kidney potatoes is their uniform tuber shape. The consistent long to oval shape of the tubers means that they not only look appealing but also cook evenly. This uniformity is highly valued by chefs, as it ensures even cooking and presentation, and by growers, as it simplifies sorting and grading during harvest.

Internal Rust Spot: Infrequent

The occurrence of internal rust spots in International Kidney potatoes is classified as infrequent, which is good news for both growers and consumers. Internal rust spots are a common defect in some potato varieties that can affect their appearance and texture. Since rust spots are rare in International Kidney potatoes, they tend to have a smoother, more visually appealing flesh that’s perfect for dishes where presentation is key.

International Kidney potatoes fresh harvest

Dormancy Period: Medium to Long

The dormancy period of International Kidney potatoes is medium to long, meaning that the tubers can be stored for a considerable amount of time before sprouting. This extended dormancy period is beneficial for both growers and consumers, as it allows the potatoes to be stored without losing quality for several months after harvest.

A longer dormancy period ensures that International Kidney potatoes remain fresh and ready for use in the kitchen well into the offseason, making them a great choice for long-term storage.

Utilization Characteristics of International Kidney Potatoes

The International Kidney potato is known for its versatility in the kitchen, making it a popular choice for a wide range of culinary applications. While it may not be ideal for every type of cooking, its unique combination of characteristics makes it a reliable option for many dishes. Let’s explore the utilization characteristics of International Kidney potatoes in detail.

Cooking Type: Fairly Firm (Multi-purpose Type)

International Kidney potatoes have a fairly firm cooked texture, which categorizes them as a multi-purpose type of potato. This texture makes them suitable for a variety of cooking methods, such as boiling, steaming, and roasting. Their firmness means they hold their shape well during cooking, making them particularly good for dishes where potatoes need to remain intact, such as salads, stews, or casseroles.

Their versatility allows them to perform well in recipes that require the potatoes to absorb flavors, such as herb-roasted potatoes or potato salads dressed in vinaigrette.

After Cooking Blackening: Little

One of the standout features of International Kidney potatoes is that they exhibit little after cooking blackening. After-cooking blackening is a common issue with some potato varieties where the flesh discolors after being cooked. With International Kidney potatoes, this problem is minimal, ensuring that your dishes maintain an attractive appearance even after cooking. This characteristic makes them a reliable choice for meals where presentation is important, such as in salads, gratins, or side dishes.

Taste: Moderate to Good

The taste of International Kidney potatoes is described as moderate to good. While they may not have the strongest flavor compared to more robust varieties, their mild, creamy taste is enjoyable and versatile. The flavor is subtle enough to complement other ingredients in a dish without overwhelming them, making International Kidney potatoes an excellent choice for simple preparations that highlight their buttery flavor. This makes them perfect for boiling and serving with fresh herbs and butter or lightly roasted with olive oil and sea salt.

Crisp Suitability: Poor

When it comes to making crisps (potato chips), International Kidney potatoes are not the ideal choice. They have poor crisp suitability, which means they don’t develop the desired crunchy texture when fried thinly. Their lower starch content and firm texture prevent them from crisping up as well as varieties specifically bred for this purpose. If you are looking to make homemade crisps, you may want to opt for a higher-starch potato variety instead.

French Fry Suitability: Poor

Similarly, International Kidney potatoes are poorly suited for making French fries. Their fairly firm texture and low to medium starch content don’t allow them to produce the light, fluffy interior, and crispy exterior that is typically desired in French fries. For those looking to make perfect fries, other potato varieties like Russets or Maris Piper are better options.

Dry Matter Content: Low to Medium

The dry matter content of International Kidney potatoes is classified as low to medium. Dry matter content refers to the proportion of the potato that is made up of solids (such as starch) as opposed to water. Potatoes with a higher dry matter content tend to be more suitable for frying or baking, as they crisp up more easily. Since International Kidney potatoes have a lower dry matter content, they maintain a firmer texture when cooked, which is great for dishes where the potato needs to hold its shape.

Starch Content: Low to Medium

In line with their dry matter content, International Kidney potatoes also have a low to medium starch content. Potatoes with higher starch content tend to be fluffier and better suited for frying or mashing, while low-starch potatoes are waxier and firmer, making them ideal for boiling and roasting. International Kidney potatoes’ low to medium starch content makes them a good choice for recipes where you want the potatoes to retain their structure, such as potato salads or oven-roasted dishes.

Resistance to Fungal Diseases in International Kidney Potatoes

The International Kidney potato is a well-loved variety for its culinary versatility and growth potential, but when it comes to resistance to certain fungal diseases, it has its strengths and weaknesses. Understanding these resistance traits can help growers take the necessary precautions to protect their crops and ensure a healthy yield. Below, we’ll explore the resistance levels of International Kidney potatoes to major fungal diseases like late blight and wart.

Resistance to Late Blight on Tubers: Low

International Kidney potatoes have a low resistance to late blight on their tubers. Late blight, caused by the fungus Phytophthora infestans, is one of the most devastating potato diseases, especially in humid conditions. The fact that International Kidney potatoes are vulnerable to this disease means that growers need to be vigilant in protecting their crops from blight outbreaks.

Preventative measures such as applying fungicides, crop rotation, and proper soil drainage can help minimize the risk of infection. It’s also important to monitor weather conditions, as late blight tends to spread more rapidly during wet and cool periods.

Resistance to Late Blight on Foliage: Low

In addition to the tubers, the foliage of International Kidney potatoes also has low resistance to late blight. This makes the entire plant susceptible to infection, starting with the leaves. Late blight on foliage can quickly spread across a field, leading to defoliation, reduced photosynthesis, and lower yields.

To combat this vulnerability, growers should regularly inspect the foliage for signs of infection, such as dark, water-soaked lesions on the leaves and stems. Early detection and the use of blight-resistant companion plants or preventive sprays can help mitigate the impact of late blight.

Resistance to Late Blight on Tubers (Laboratory Test): Low

Laboratory tests confirm that International Kidney potatoes show low resistance to late blight on their tubers. This scientific confirmation further underscores the need for careful crop management practices to minimize the risk of blight infection. Late blight can cause significant losses if left unchecked, as infected tubers can rot in the ground or in storage, resulting in both immediate and long-term damage to the harvest.

Resistance to Late Blight on Foliage (Laboratory Test): Low

Similarly, laboratory tests also confirm low resistance to late blight on the foliage of International Kidney potatoes. The combination of susceptibility in both the foliage and tubers makes late blight a particularly dangerous threat to this variety. Farmers should consider a proactive approach, using integrated pest management strategies that combine chemical treatments, environmental controls, and crop surveillance to limit the spread of late blight.

Resistance to Wart (Synchytrium endobioticum): Field Immune

One area where International Kidney potatoes excel is their field immunity to wart, a disease caused by the fungus Synchytrium endobioticum. Wart is a highly destructive disease that affects the tubers, causing them to become deformed and unusable. Fortunately, International Kidney potatoes are field immune to warts, meaning they are not affected by the disease under normal growing conditions.

This immunity is a major advantage for growers, especially in regions where warts have been a problem. Wart can persist in soil for many years, so planting immune varieties like International Kidney can help prevent the spread and recurrence of the disease.

Field Immunity to Wart Races: Race 1

International Kidney potatoes are specifically immune to Race 1 of the wart disease, the most common strain of the fungus. This immunity further solidifies the variety’s resilience against one of the more persistent and damaging fungal diseases affecting potatoes. However, it is important to note that while the potato is immune to Race 1, it may still be vulnerable to other races of the wart fungus, though these are less commonly encountered.

Resistance to Bacterial Diseases in International Kidney Potatoes

In addition to fungal diseases, bacterial diseases can pose a significant threat to potato crops. The International Kidney potato has specific resistance traits when it comes to bacterial diseases, particularly common scab, which can impact the quality and appearance of the harvested tubers. Below, we explore the potato’s resistance to bacterial diseases based on the available data.

Resistance to Common Scab (Streptomyces scabies): Medium to Medium-High

The International Kidney potato shows medium to medium-high resistance to common scab, a bacterial disease caused by Streptomyces scabies. Common scab is a soil-borne disease that primarily affects the skin of potato tubers, leading to rough, raised, or pitted lesions on the surface. While it doesn’t usually affect the internal quality of the potato, it can make the tubers less appealing for commercial sale or culinary use, as the scabby lesions can be unsightly and difficult to peel.

What Does Medium to Medium-High Resistance Mean?

With medium to medium-high resistance, the International Kidney potato is less likely to develop severe cases of common scab compared to more susceptible varieties. This level of resistance means that under typical growing conditions, the potato can fend off the infection to a significant degree, though it is not completely immune.

Growers may still see occasional cases of common scab, but the damage is likely to be less severe and widespread. This makes International Kidney a relatively reliable choice in regions where common scab is a known issue, especially if combined with proper management techniques such as:

Soil pH control: Lowering soil pH (to around 5.0 to 5.2) has been shown to reduce the occurrence of common scab.
Crop rotation: Rotating potatoes with non-host crops can help prevent the buildup of Streptomyces scabies in the soil.
Adequate irrigation: Ensuring consistent moisture levels during tuber development can help minimize the risk of common scab.

Impact on Potato Quality and Yield

While common scab primarily affects the external appearance of the tubers, its presence can still lower market value or consumer appeal, particularly in varieties like International Kidney, which are known for their smooth skin. The medium to medium-high resistance exhibited by this potato variety reduces the likelihood of widespread infection and helps preserve the quality and visual appeal of the harvested tubers.

Resistance to Viral Diseases in International Kidney Potatoes

Viral diseases are another major concern for potato growers, as they can significantly impact both crop quality and yield. The International Kidney potato exhibits varying levels of resistance to different viral diseases, making it important for growers to understand how best to manage their crops in light of these vulnerabilities and strengths. Let’s take a closer look at the potato’s resistance to key viral diseases.

Resistance to Potato Virus A: Low

The International Kidney potato has low resistance to potato virus A (PVA), meaning it is relatively susceptible to infection by this virus. Potato virus A can cause symptoms like leaf mottling, stunting, and reduced yield, though the severity of the disease can vary depending on environmental factors and the presence of other viruses.

Due to the low resistance, growers need to monitor crops closely and employ virus management strategies such as:

Use of certified virus-free seed potatoes to minimize the risk of introducing PVA into the field.
Control of aphids, which are the primary vectors for transmitting PVA between plants.
Crop rotation and good field hygiene to reduce the spread of the virus.

Resistance to Potato Virus X: Low to High

The resistance of International Kidney potatoes to potato virus X (PVX) is listed as low to high, indicating that the resistance can vary depending on specific conditions or strains of the virus.

Low resistance to PVX means that under certain conditions, International Kidney potatoes may be susceptible to this virus, which typically causes mosaic patterns on the leaves and a reduction in overall crop yield.
However, the variety can exhibit high resistance in other cases, particularly in environments where the strain of PVX is less aggressive or where growers take proactive management steps to prevent infection.

PVX is often less damaging than other viruses, but it can still reduce plant vigor, especially when combined with other viral infections. As with PVA, certified virus-free seed and aphid control are critical in managing the spread of PVX.

Resistance to Potato Virus Y: Medium to High

The International Kidney potato shows medium to high resistance to potato virus Y (PVY). PVY is one of the most serious viral diseases affecting potatoes, causing symptoms like leaf yellowing, necrosis, and significant yield loss.

With medium to high resistance, International Kidney potatoes are generally able to withstand the effects of PVY better than more susceptible varieties. This resistance is especially valuable in regions where PVY is prevalent, as it can help reduce the impact of the virus on both crop quality and yield.

Growers should still implement virus management practices, especially in areas where PVY is known to be an issue. Resistance to PVY can vary depending on the specific strain of the virus, so monitoring and preventive care remain essential.

Resistance to Potato Leaf Roll Virus: Medium to High

The International Kidney potato also demonstrates medium to high resistance to potato leaf roll virus (PLRV), another significant viral disease that can cause rolling of the leaves, plant stunting, and severely reduced yields. PLRV is transmitted by aphids and can lead to major economic losses if not managed properly.

The medium to high resistance means that International Kidney potatoes are fairly well protected against the worst effects of PLRV, though occasional infections may still occur. Controlling aphid populations is a critical component of managing PLRV, as is ensuring that seed potatoes are certified virus-free.

Resistance to Pests in International Kidney Potatoes

In addition to fungal, bacterial, and viral diseases, pest resistance is a critical factor in determining the overall health and yield of potato crops. The International Kidney potato has specific vulnerabilities when it comes to certain pests, particularly nematodes like Globodera rostochiensis (also known as the golden potato cyst nematode). Below, we examine the pest resistance of this potato variety based on the provided data.

Resistance to Globodera rostochiensis Race 1: Low

The International Kidney potato shows low resistance to Globodera rostochiensis race 1, a nematode species that causes significant damage to potato crops. Globodera rostochiensis is a parasitic roundworm that infects the roots of potato plants, leading to stunted growth, yellowing of the foliage, and severely reduced yields. Infested fields can experience long-term problems as the nematode cysts can remain viable in the soil for many years.

What Does Low Resistance Mean?

With low resistance to this pest, International Kidney potatoes are highly susceptible to infestations by Globodera rostochiensis race 1. Once infected, the nematodes create cysts on the roots, which disrupt the plant’s ability to absorb water and nutrients, eventually weakening the entire plant. This can lead to significantly reduced yields and poor-quality tubers, making the management of this pest crucial for the success of the crop.

Managing Globodera Rostochiensis Infestations

Given the low resistance of International Kidney potatoes to Globodera rostochiensis race 1, effective pest management strategies are essential for minimizing crop damage. Some important practices include:

Crop rotation: Rotating with non-host crops (such as cereals or legumes) can help reduce nematode populations in the soil, as these crops do not support the lifecycle of the nematode.
Resistant varieties: In fields with a known nematode problem, it may be necessary to alternate with potato varieties that are resistant to Globodera rostochiensis.
Soil fumigation or nematicides: Chemical treatments can help reduce the number of viable nematode cysts in the soil, though these methods can be costly and may have environmental impacts.
Field hygiene: Cleaning equipment and avoiding the movement of contaminated soil between fields can help prevent the spread of the nematode.

When to plant International Kidney potatoes in the UK?

In the UK, the best time to plant International Kidney potatoes depends on the local climate and the growing conditions, but they are generally planted in early spring, from March to April. This timing allows the potatoes to grow through the warm months, ensuring a good harvest.

Here’s a breakdown of the planting guidelines for International Kidney potatoes in the UK:

1. Soil Preparation

Start preparing the soil in late winter (February) if the ground is workable. Ensure the soil is well-drained and rich in organic matter.
If the soil is too wet, wait until it dries out a bit to avoid waterlogged conditions.

2. Frost-Free Period

Wait until the risk of frost has passed before planting. Frost can damage young plants, so for most parts of the UK, this is typically late March to early April.
In milder regions, such as the south and west, you can plant earlier in late March.
In colder northern or higher altitude areas, consider delaying planting until late April to avoid frost risk.

3. Chitting (Pre-Sprouting)

About 4-6 weeks before planting (from late January to February), start chitting your International Kidney seed potatoes. Place them in a cool, light place to encourage shoots to develop before planting.
This helps give the potatoes a head start and improves the likelihood of a strong, early growth season.

4. Planting Depth and Spacing

Plant the chitted tubers in rows, about 10-15 cm (4-6 inches) deep, with 30 cm (12 inches) between plants and 60 cm (24 inches) between rows.
International Kidney potatoes are a spreading variety, so give them enough room to grow.

5. Cover and Protection

If frost is still a concern, cover the potato beds with fleece or horticultural fabric to protect young shoots.
Earthing up the soil around the plants as they grow also provides added protection against late frosts.

When to harvest International Kidney Potatoes in the UK?

International Kidney potatoes are ready to harvest in late summer (typically from July to August) if planted in spring, especially if they are grown for early varieties like Jersey Royals.

By following these guidelines, you can ensure a successful planting season for International Kidney potatoes in the UK.

Conclusion

The International Kidney potato is a tasty and versatile variety, known for its smooth skin and creamy flesh. It grows well in many conditions but needs attention to protect it from certain diseases. It’s vulnerable to late blight and a few viruses, so you’ll need to watch out for those. On the plus side, it’s resistant to wart disease and does fairly well against common scab.

In the UK, plant these potatoes from March to April after the last frost, and they’ll be ready to harvest by July to August. With the right care, you can enjoy a healthy crop!