Best grow bags

Growing bags are popular with gardeners - and for good reasons. You don't need a pot as you can plant directly into the bag and for tender crops they're a great alternative to planting in a greenhouse border. They're a bargain option, too - often costing less than bags of multipurpose compost.

But not every bag is as great as it sounds, which is why we test them for you. We trialled 10 growing bags, most of which were peat-free, to find the best for growing summer veg, such as cucumbers, tomatoes, aubergines, chillies, peppers and melons. The best produced lots of large, healthy summer vegetables, while the worst made inadequate yields with pale leaves.

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Best grow bags

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USING THE TABLE The more stars the better. OVERALL SCORE Ignores price and is based on: weight of cucumbers per bag 50%; number of cucumbers per bag 20%; mean cucumber weight 20%; plant vigour after seven weeks 10%. 

Not found the right product for you? Browse all our compost reviews.

Why Which? grow bag reviews are better

Before testing, we send out four secret shoppers to buy all our grow bags in garden centres and DIY stores. They buy two of each, making a total of eight of each brand, to see if there are any variation in the quality of each bag.

We grow cucumber plants for this trial as they grow quickly, and those in good bags produce excellent harvests. We have found tomatoes take a long time to mature, meaning a great reliance on liquid feed which hides the true results from the grow bags. 

In late May, when the plants each have five leaves we plant two into each of our growing bags. We grow them in a greenhouse, trained up wires and remove sideshoots below the fruit.

We link each growing bag to an automatic watering system, so all the bags receive the same amount of water, and feed those that require it with a liquid fertiliser. Some of our bags already contain enough fertiliser to last through our trial. 

We grow and pick the cucumbers twice a week. We weigh and count the harvest from each bag over an eight-week period, noting if any are bendy, bulbous or have rough skins. At the end of the test, we harvest, weigh and grade the remaining cucumbers for size.

To find out more, head to how we test compost. Alternatively, browse our controlled-release feeds.

How to use grow bags

1. Sow your seeds in around March and keep them inside on a sunny windowsill until they are large enough to plant in your bag (around 15cm) and the last frost has gone. 
2. Put your grow bag in its final position and gently roll it to fluff up the compost.
3. Make some cuts in the bottom of the bag to allow excess water to drain out.
4. Cut along the marked lines on the top of the growing bag to position your plants. 
5. If you only want to put two plants in each bag, use the two outer-planting positions on the bag.

How do you water plants in a grow bag?

• Water regularly so the bag doesn’t dry out. In hot weather, this may need to be up to three times a day.
• An automatic watering system with a timer will help to avoid dry plants.
• Most summer veg will be in the bags for many weeks, so you’ll need to feed them. Either add controlled-release feed by mixing it into the compost where you have cut holes before you plant, or liquid feed twice a week once the first fruits have formed. Follow the dosage and frequency advice on the bottle.

For more advice on choosing the best compost for you, head to our compost testing results.