2nd August 2021
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 we decided to test them for you. We trialled 11 peat and peat-free growing bags 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.
Harvest of best-quality cucumbers
Harvest of misshapen cucumbers
Mean fruit weight
Peat content: 45%
The compost mix in this growing bag contains less peat than many bags on test this year – the rest is made up of wood fibre, green compost, manure and seaweed.
It’s one of the largest bags on test and in past years we’ve found that larger bags often give better results. It certainly gave the heaviest harvest, with almost 12kg of cucumbers per bag. Plus it produced more good-quality cucumbers than any of the other bags on test.
Peat content: 70%
Cheap but high peat
As the name suggests, the compost in this bag is a traditional high-peat mix, albeit with added wood fibre, manure, seaweed and green compost (made from composted green-waste collections).
It’s also smaller than many other bags, so bear this in mind if you want to grow a lot of tomatoes or cucumbers.
The two plants we grew in this bag were very healthy and gave us a heavy crop of straight cucumbers, but were slightly smaller than others.
Peat content: 60%
Organic, but not peat-free
This compost and the feed within this bag have been certified as organic by Organic Farmers &Growers, a body that certifies organic foods and feeds. However, don’t confuse ‘organic’ with‘ peat-free’, as this bag contains 60% peat, along with wood fibre and bark.
It’s described as a two-plant planter, but the small print recommends only one cucumber plant.
We grew two and found the bags were plenty large enough to cope, giving us lots of excellent, supermarket-quality cucumbers.
Peat content: 0%
Best peat-free bag
This peat-free planter is made from composted bark and coir, but with a small amount of carefully screened green waste. It’s approved by the Organic Soil Association as both the compost and the feed are organic. The instructions on the bag recommend liquid feeding after three to four weeks.
The bags produced a good number of cucumbers, and cumulatively they were one of the heaviest harvests. However, there were a larger proportion of misshapen cucumbers, suggesting this compost needs more watering than others.
Before testing, we send out four secret shoppers to buy all our grow bags so we know we're getting the same product as you. The shoppers 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 sow seeds of cucumber ‘Carmen’, a standard-sized cucumber, which grows fast and produces good harvests. 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 removed 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 them with a liquid fertiliser.
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.