Advice
RHS Help & Advice
Planting potatoes in containers
Fresh potatoes taste so much better than bought ones, and there is a huge choice of cultivars available to the home gardener, including many that are unavailable in the shops, or very expensive. Tasty, unusual, new and salad potatoes can be grown in a pot on a patio or balcony - you do not even need to have a garden.
In this step-by-step guide, we show you how to grow potatoes in a tub.
Chitting
Buy fresh seed potatoes from a reputable supplier, as these will be guaranteed virus-free, and will be almost completely free of other pests and diseases.
The tubers need to be chitted (i.e. sprouted), in order to accelerate their maturity and shorten the growing time needed to get a good crop of new tubers.
In late winter to early spring, place the tubers in an old egg-box, or lay them out in a tray. Position them so that the end or face with the largest number of eyes is facing up to the light.
Place the trays in an unheated, frost-free room, in filtered light (not direct sunlight).
Depending on the region where you live, you can start chitting in January or early February (mild southern districts), or in late February or March (colder districts). They should take about six weeks to sprout.
After about six weeks, the sprouts should be about 5cm (2in) long, and dark in colour. Pale spindly sprouts suggest that the temperature is too warm or that light levels are insufficient. If the sprouts are tiny or very slow to appear, try increasing the temperature slightly to encourage them.
Preparing the container
Use a large pot - at least 30cm (12in) across and deep, with drainage holes. If you do not have a suitable pot, you can use a polystyrene or plastic crate, or even an empty compost bag, but you will need to make drainage holes in the base first.
Place broken pottery, stones or polystyrene crocks in the bottom of the container. These will cover the drainage holes and prevent them getting clogged up with compost.
Place a layer of compost 10cm (4in) deep in the bottom of the pot. Growing-bag compost works well as it leaves the potatoes very clean, but you could also make your own mixture of loamy garden soil and compost or manure.
Planting
Place two or three tubers in each pot, positioning them on the surface of the compost. Potato cultivars that produce small tubers, or those that give lower yields, can be planted a bit closer together (three to a 30cm pot) than larger or high-yielding potatoes (which should be planted two to a 30cm pot).
If some of your seed tubers are very large, you can cut them in two. As long as each piece has a good crop of sprouts, they will do fine.
Cover the tubers with another 15cm (6in) of compost.
If the compost is dry, water in the tubers until the water drains out of the drainage holes. If the compost is damp, you can probably avoid watering until shoots start to appear. Place the pot in a bright, sheltered position.
Earthing up
When the shoots reach 15cm (6in) tall, add another 10cm (4in) layer of compost on the top. This prevents light from reaching the tubers, and stops them turning green.
Repeat the process of earthing up as the stems lengthen - just leave enough uncovered to allow some leaves to absorb sunlight and grow.
General maintenance
Unless the weather is very hot and dry, you may not need to water your potatoes until they start to flower. This usually coincides with the tubers being about marble size and starting to swell. The plants need most water when the tubers are swelling. Some cultivars do not flower - in this case, you can scrape away a bit of earth from the top to see if tubers have started forming, and water accordingly.
Give a liquid feed (a tomato fertiliser, for example), at regular intervals as per the manufacturer’s instructions. Do this even if you have mixed in controlled-release granules on planting, as potatoes are heavy feeders.
Be aware of, and diagnose common potato problems, including:
- Black scurf
- Blight
- Potato cyst eelworm
- Powdery scab
- Rots
- Skin problems, including common scab
- Slug damage
- Viruses
Harvesting and storing
Check the size of the tubers by scraping away the compost from the surface of the pot and having a look. Some very early cultivars are ready when the plants come into flower, or soon after, so flowering time is the time to start checking your tubers regularly. Harvest them when they look a good size for eating. The longer you leave the tubers in the pot, the more prone they become to slug damage. Let the tubers dry out in the sun for two to three hours before storing them in paper bags or crates.
Cultivar selection
First earlies tend to do better in pots than others. Some second earlies are alright, but maincrops are best avoided, as are varieties that produce stolon type roots (which are similar to runners, and need more space than a pot can provide).
Potato ‘Mimi’ AGM was found by the RHS Vegetable Trials Committee to be particularly suited to container growing, but many other first earlies (such as ‘Amandine’ and ‘Annabelle’) would be fine, as would ‘Charlotte’, a second early salad potato with a good flavour and firm texture.
Maya Albert