You can grow potatoes without an allotment. A sturdy growing bag, a sunny corner and a few certified seed potatoes are enough to give this crop a try. Bags are especially useful on patios because you can add compost around the shoots as they grow and tip out the contents when the potatoes are ready. The biggest mistakes are planting too many tubers, letting the bag dry out and forgetting to provide drainage.
Choose the right potatoes
Potato varieties are described as first earlies, second earlies or maincrop, based mainly on their growing season. First earlies are an excellent choice for containers: they develop relatively quickly and you can pick small, tender new potatoes. Maincrop varieties need longer and generally take more space.
Buy certified seed potatoes from a garden centre or reputable supplier. These are produced for planting and are a better choice than ordinary supermarket potatoes, which may carry diseases or have been treated to discourage sprouting.
What kind of bag do you need?
Purpose-made potato bags have drainage holes, reinforced handles and enough depth for compost to be added gradually. A strong reusable container or suitably prepared compost sack can work too, provided it drains freely.
Choose a bag that will hold enough compost for healthy root growth. A deep, broad container is easier to water evenly than a narrow sack with potatoes crammed into the bottom. Don't plant several seed potatoes into a tiny bag because that often gives a disappointing collection of small tubers.
Chitting potatoes before planting
Chitting means allowing small shoots to develop on seed potatoes before they go into compost. It is often used for early varieties and can give them a head start. Place seed potatoes in a cool, bright, frost-free location with their eyes facing upwards where practical.
An empty egg box can stop tubers rolling around. The RHS describes planting when shoots have developed to a few centimetres long. Avoid leaving them in a dark cupboard, where sprouts can become long, pale and fragile.
When to plant potatoes in bags
First earlies are commonly planted in spring. The precise date depends on location, variety and whether the bag can be moved under cover during frost. Young shoots are vulnerable to freezing temperatures even when tubers remain beneath the compost.
In a colder area, such as much of northern England, starting in a protected greenhouse or waiting until conditions improve is often safer than leaving new shoots exposed. Don't put a newly planted bag against a hot radiator indoors; potatoes need light and appropriate growing conditions once they emerge.
How to plant seed potatoes in a bag
Start by folding down the sides if the bag design allows. Add a layer of peat-free multipurpose compost at the bottom. Position the seed potatoes with their shoots facing upwards and space them apart so they have room to develop.
Cover with more compost and water gently. Follow the bag's capacity and the seed supplier's advice for how many tubers it should hold. For many ordinary-sized growing bags, one to three seed potatoes is more sensible than packing in half a dozen.
What does earthing up mean?
As shoots get taller, add more compost around their lower stems, leaving healthy top growth exposed. This is called earthing up. It helps prevent developing potatoes from reaching the surface and becoming green in daylight. It can also provide some protection from a late cold snap.
Gradually unroll the bag sides as you raise the compost level. Continue until the container is filled to a practical height. Don't bury the plant's entire leafy canopy repeatedly; it needs exposed leaves to make energy.
The RHS points out that earthing up is chiefly about protecting tubers and young shoots, not a guaranteed way to multiply your harvest. Good light, healthy roots and steady watering remain important.
Watering potatoes in containers
Growing bags can dry rapidly in warm weather, especially when plants have developed lots of foliage. Check moisture below the surface rather than watering by the clock. Water thoroughly when needed, allowing excess to run through the drainage holes.
Waterlogging is also harmful. A heavy, wet bag with yellowing plants may have poor drainage or struggling roots. Adding more water will not revive roots that have been sitting without enough air.
In very hot weather, placing the bag where roots stay relatively cool while the leaves receive adequate light can help. Avoid continually moving a heavy, established container or damaging stems.
Do you need to feed potato plants?
Fresh compost provides nutrients at the beginning. Potatoes grown in a bag may benefit from a suitable vegetable fertiliser where nutrients become depleted. Follow the product's recommendations and avoid excessive feeding, which can encourage a mass of foliage without improving the crop.
Healthy potato leaves should normally be vigorous green. If the plant looks stressed, check water supply, drainage, disease and light before assuming it needs additional feed.
When are bag-grown potatoes ready?
For first earlies, you can often harvest small new potatoes when the plants have grown and developed useful tubers, usually around flowering time or according to the variety's expected maturity. You can carefully feel in the compost near the side for a few potatoes if you want to check without emptying everything.
For potatoes intended to mature fully, allow the crop to develop until foliage naturally begins to yellow and die back, provided it remains healthy. Timing varies with variety and weather.
If foliage is killed by blight or severe frost, take appropriate action and don't confuse sudden disease damage with normal maturity. Look for spreading brown lesions and check current guidance if blight is suspected.
How to harvest potatoes from a growing bag
Move the bag to a clean surface or large tray and tip the compost out carefully. Search through the material with your hands rather than thrusting a fork into it and piercing the tubers. You may be surprised how far into the compost the potatoes have developed.
Set aside damaged potatoes to use promptly if otherwise sound. Brush loose dirt from sound tubers and allow them to dry appropriately before storing. Early new potatoes are best eaten fresh; they don't have the same storage qualities as properly matured maincrop potatoes.
Discard green potatoes. Light exposure can lead to increased levels of natural toxins, and the RHS advises against eating green tubers. Potato fruits, which sometimes develop after flowering, are also poisonous and must not be eaten.
Common problems with potatoes in bags
Lots of leaves but few potatoes: Plants may be overcrowded, overfed or harvested too soon. Check the variety and its usual maturity period.
Bag dries out repeatedly: Use more generous compost volume next time, inspect more often and water thoroughly.
Green tubers: Add sufficient compost to cover developing potatoes and keep light away from the crop.
Leaves blacken suddenly: Frost and blight are different possibilities; inspect the pattern and timing before acting.
Small or damaged crop: Root competition, poor drainage, pests and irregular watering can all play a part.
What to change next season
After harvesting, inspect the bag for tears and blocked drainage holes. Don't assume the used compost will be equally suitable for another potato crop without replenishing nutrients or considering disease risk. Avoid returning diseased material to your growing containers.
Start with one early variety and a bag you can water comfortably. It's an inexpensive way to learn how potatoes grow, and even a modest harvest can be satisfying.
Sources
Royal Horticultural Society: How to Grow Potatoes in Containers and How to Grow Potatoes.