A boon for gardeners with limited space
Growing tomatoes in grow bags are handy for gardeners with little (or no space) to plant in proper beds. However, there are pitfalls you need to be aware of. Here are my top tips for getting your money’s worth and the biggest crops out of soil in sacks.
One point to note here – if you want to use peat-free grow bags, they are getting easier to find. If you can’t find a peat-free grow bag, use peat-free compost in pots, or ring culture pots. Read more about growing tomatoes under glass and in pots.
You get what you pay for
Don’t fall for bargain basement grow bags, especially when sold at ‘non-gardening’ stores. The compost will be bulked out with filler, they will be small and need more frequent watering and feeding.
Growing tomatoes in grow bags – Buy the biggest you can find
Usually labelled as ‘extra large’ with a capacity of 50-55 litres, compared with 25-33 litres. The dimensions of grow bags (length x width) are usually standard. Made to fit into one-size drip-proof trays, the depth changes. This extra depth means a better root system can develop. Those times when you invariably forget to water won’t be so critical.
Do you need actual ‘tomato bags’?
That’s your choice and you’ll buy generic bags more cheaply if cost is an issue. However, add food containing a lot of potash.
Growing tomatoes in grow bags – How long they will feed plants?
Most of the market leaders for tomato bags will feed for about six weeks with a high potash feeder. After then, it’s up to you to feed plants weekly or fortnightly.
Do they have moisture-retentive particles?
Not necessary if you’re regular with watering. However, they’re but a life-saver for the plants if you have a life! Buy the granules separately and add them before you plant.
Growing tomatoes in grow bags – Use ring culture pots
These are basically large plant pots with no bottom (you can make your own) that sit on top of the grow bag. They give extra area for the root run. You can also buy a host of grow pots (with an outer ‘moat’ to deliver water slowly direct to the lower roots and ‘plant haloes’ some of which have supports for canes built-in. I use a combination of the two. I like ordinary ring culture pots – they’re cheap, plastic ones last forever and they hold more soil than the ‘moat’ varieties.
Cane support
A must for indeterminate (cordon) varieties, which you tie into a stake. If you’re using a grow bag flat with no ring culture pot on top, this can be a problem. There is no depth of soil to keep the canes upright. Solution – ring culture pots (put the canes in first, then the plant). Crocus has a support set available.
Growing tomatoes in grow bags – A tight fit
When using ring culture pots, don’t plonk them on the top and hope for the best. Standard plastic pots have a 0.5cm inward rim at the bottom. Mark on the bag where this line is then cut out the hole. As it’s smaller than the outside, push and twist the pot into the grow bag hole (easier than it sounds, as it’s quite stretchy). You then have a relatively watertight seal so water can seep slowly into the soil. Pots with moats often have ‘teeth’ that mark out the pot shape.
Mini-greenhouses
Most models fit grow bags but I use the bare frames to support my cordon plants and canes. It’s a cheap and easy way to stop them from keeling over.
Growing tomatoes in grow bags – Be creative
Look at turning bags on their side and planting in the top (useful for other plants or if you don’t want to invest in ring culture pots, etc). The soil depth means canes will be held securely.
