Recognising Potato Plant Harvest Readiness
Determining when potato plants are ready for harvest involves observing specific visual indicators on the foliage and understanding the expected growth cycle. The most common sign is when the plant’s leaves and stems begin to turn yellow and die back, signalling that the tubers below have matured. This natural decline is the plant's way of preparing for dormancy after the energy-intensive process of tuber formation.
- Foliage turning yellow and dying back is the primary indicator.
- Stem and leaf wilting signal tuber maturity.
- New potatoes are ready earlier, before full foliage die-back.
- Maincrop varieties need the plant to nearly fully wither.
For new potatoes, the harvest can typically begin a few weeks after the plants start to flower. At this stage, the plant's leaves will still be largely green, but you might notice some yellowing appearing. New potatoes are smaller, have thin, delicate skins that rub off easily, and are best eaten soon after harvesting as they do not store well. If your aim is to gather these tender, early crops, you can carefully dig around the base of the plant with your hands or a small trowel, taking only a few tubers and leaving the plant to continue growing for larger maincrop potatoes.
Conversely, maincrop potatoes require the plant to mature fully. This means waiting until the foliage has significantly yellowed, wilted, and started to wither away completely. This process can take anywhere from 70 to 120 days, depending on the potato variety. The plant's energy has by this point been fully transferred to the tubers, which have grown to their full size and developed a tougher skin, making them suitable for storage over the winter months. Rushing the harvest for maincrop varieties before this stage means smaller yields and potatoes that are not yet ready for long-term keeping.
The Role of Flowering in Potato Growth
While not a definitive harvest signal, the flowering stage of a potato plant offers a clue about its progress. For many varieties, flowering begins roughly six to eight weeks after planting the seed potatoes. For new potatoes, this flowering period is often the cue to start looking for the first signs of readiness. You can gently scrape away a little soil near the stem to check the size of developing tubers. However, for maincrop varieties, flowering is just a milestone; the plant needs considerably more time to develop its full potential for storage.
It is important to distinguish between the different types of potatoes you might be growing. First early varieties mature quickly, often within 10-12 weeks, and may be ready to harvest around the time they start flowering or shortly after. Second early varieties take a little longer, typically 12-14 weeks, and will show more significant yellowing of the foliage before they are ready. Maincrop varieties are the slowest, requiring 16-20 weeks or more, and will almost completely die back before they are deemed ready for digging up.
The condition of the stems is also a vital indicator. Initially, the stems are turgid and upright, supporting lush green leaves. As the plant approaches maturity, especially for maincrop types, these stems will begin to lose their rigidity, appearing limp and starting to turn yellow or brown. This transition from vibrant green to yellow and then brown is a visual countdown to harvest. If you are growing potatoes in growing bags for potatoes or in containers, the signs remain consistent with those grown directly in the ground, though monitoring soil moisture becomes even more critical.
When to Harvest: Timing for Different Potato Types
The exact timing for harvesting potatoes is less about a fixed calendar date and more about observing the plant's life cycle and maturity indicators. Different potato varieties are bred for different maturation periods, and this significantly dictates when you should be looking to lift your crop. Understanding these differences is key to maximising your yield and ensuring the quality of your harvest, whether you plan to eat them straight away or store them.
Timing is everything for both new and maincrop potatoes.
New potatoes, often referred to as 'earlies', are typically ready to harvest from around six to eight weeks after planting. At this point, the plant will likely still be green and possibly even flowering, but the tubers will have reached a usable size. Their skins are thin and easily damaged, meaning they are not suited for long-term storage but are prized for their delicate flavour and waxy texture. If you are growing potatoes in pots or containers, you may find you can harvest new potatoes slightly earlier by carefully reaching into the pot and selecting larger tubers without disturbing the entire plant.
Maincrop varieties, on the other hand, require a much longer growing season, usually between 16 and 20 weeks, sometimes more. These are the potatoes intended for storage. You should resist the temptation to dig them up prematurely. Wait until the foliage has turned yellow, withered, and started to die back substantially. This indicates that the tubers have reached full size and their skins have hardened sufficiently to withstand storage. Harvesting too early will result in smaller, less mature tubers that are prone to damage and rot if stored.
Preparing for the Harvest
Once you've identified that your potato plants are showing signs of readiness, it is advisable to stop watering them a week or two before the intended harvest date. This helps the skins on the tubers to harden, reducing the risk of damage during digging and improving their storage capabilities. If the weather is very wet, you might need to take extra care, as excessively damp conditions can encourage rot in stored potatoes.
For maincrop potatoes, it is often recommended to cut the haulms (the leafy stems) down to about 15 cm (6 inches) from the ground a week or two before you plan to dig them up. This can help to further harden the skins of the tubers and also makes it easier to manoeuvre around the plants when you come to harvest. It also prevents any disease that might be present on the leaves from infecting the tubers.
When digging, it is best to use a garden fork or a spade, and start by inserting it into the soil a good distance away from the plant's stem. This minimises the chance of spearing the tubers themselves. Work your way around the plant, loosening the soil and carefully lifting the entire clump of potatoes. It is common to find some tubers missed by the first pass, so a thorough search of the disturbed soil is always worthwhile.
How to Check for Potato Maturity
You can actively check for potato maturity by carefully inspecting the foliage and, if necessary, gently probing the soil. The most obvious visual cue is the plant's overall decline, but there are nuances to consider for different types and stages of growth. Patience is a virtue when growing potatoes, especially for maincrop varieties destined for storage.
Gently scrape away a small amount of soil with your fingers or a small trowel near the main stem to check the size and skin texture of a few tubers without disturbing the entire plant.
For new potatoes, once the plants have flowered, you can begin to check their readiness. Carefully dig around the base of the plant with your hands or a small trowel. You are looking for tubers that have reached a size you are happy with – typically around 5-7 cm (2-3 inches) in diameter. The key characteristic of new potatoes is their delicate, easily-rubbed-off skin. If the skin is thin and easily removed, they are ready.
With maincrop varieties, the visual signs are more pronounced. You want to see the foliage turn a significant shade of yellow and begin to droop. The stems will become limp, and the leaves will start to wither. This process signals that the plant has finished its growing phase and has channelled all its energy into the tubers. If the plant is still lush and green, it is likely still actively growing and producing more tubers, or enlarging existing ones. Waiting until the plant is well into its die-back phase ensures that the tubers have reached their maximum size and have developed firmer skins suitable for storage.
Digging Up Your Potatoes: Techniques and Best Practices
The actual process of digging up potatoes is straightforward but requires care to avoid damaging the crop. For new potatoes, you can often carefully unearth them by hand or with a small trowel, taking only what you need. This approach allows the remaining tubers on the plant to continue growing larger.
For maincrop potatoes, the goal is to harvest the entire yield. Begin by carefully inserting a garden fork or spade into the soil a fair distance away from the base of the plant. This is crucial to avoid cutting or piercing the tubers. Lift the soil and the plant, and gently shake off excess soil. Turn the clump over and carefully pick out the potatoes. It is worth sifting through the soil again, as smaller tubers can sometimes be missed.
Avoid washing potatoes intended for storage. Gently brush off any excess soil with a soft brush or a dry cloth. Washing can introduce moisture, which encourages rot and reduces their shelf life. If the soil is very sticky, you can leave them to dry slightly in the sun for a few hours (but not too long, as this can cause them to turn green and produce solanine, which is toxic).
Once harvested, allow the potatoes to cure for a week or two in a cool, dry, dark, and well-ventilated place. This process helps to heal any minor skins abrasions and further toughens the skins, making them more resilient for storage. This curing step is particularly beneficial for maincrop varieties that you intend to keep for several months.
Post-Harvest Care for Stored Potatoes
Successfully harvesting your potatoes is only part of the process. How you handle them after digging significantly impacts their storage life and quality. Proper curing and storage conditions are vital for keeping your maincrop potatoes edible for months.
Store harvested potatoes in a cool, dark, and well-ventilated place, ideally between 7-10°C (45-50°F), away from direct light and moisture.
After digging, the first step is to cure the potatoes. This involves allowing them to dry and heal any minor surface damage. Spread them out in a single layer in a cool, dry, dark, and well-ventilated area for about one to two weeks. Avoid direct sunlight, as this can cause the potatoes to turn green and produce solanine, a toxic compound. Do not wash your potatoes before storage; simply brush off any loose soil. Washing can introduce moisture, which promotes rot and shortens shelf life.
Once cured, the potatoes are ready for long-term storage. The ideal storage temperature is between 7-10°C (45-50°F). Temperatures above 10°C (50°F) can encourage sprouting, while temperatures below 4°C (40°F) can convert their starches into sugars, affecting their taste and cooking properties, and potentially causing them to turn black when cooked. A cool pantry, cellar, or unheated garage can be suitable.
Crucially, potatoes must be stored in the dark. Light exposure will cause them to turn green and sprout, making them unsuitable for consumption. Use breathable containers such as hessian sacks, wooden crates, or cardboard boxes. Avoid plastic bags or sealed containers, as these trap moisture and prevent air circulation, leading to spoilage. Ensure there is good airflow around the potatoes to prevent condensation from building up.
When to Discard Stored Potatoes
Regularly inspect your stored potatoes. Remove any that show signs of disease, rot, or significant sprouting immediately to prevent them from affecting the rest of the crop. Potatoes that have turned green should be discarded or, if the green part is small, cut away completely before cooking, though it is safer to avoid them altogether. Sprouts can be removed, but if the potato has become soft and shrivelled, it is past its best.
The shelf life of stored potatoes varies depending on the variety, the initial quality, and the storage conditions. Well-stored maincrop varieties can last for several months, sometimes up to six or more. New potatoes, with their delicate skins, are much more perishable and are best consumed within a week or two of harvesting, even if refrigerated.
When preparing to cook, always check your potatoes. If a potato has only minor sprouts and is still firm, you can typically remove the sprouts and any green areas and use the rest. However, if the potato is soft, wrinkled, or has extensive greening or soft rot, it is best to discard it to avoid any health risks associated with solanine poisoning or consuming spoiled food.