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What Size Of Grow Bag Do You Need?

If gardening in a greenhouse or poly tunnel you may well be using grow bags. But there are so many different sizes of grow bags available, what size do you need?

Size of grow bag
Tomato in Grow Bag

For me, the answer to this is simple, the bigger the better. Get the biggest grow bag you can for your budget and space.

The bigger the grow bag you have the more room there will be for the roots of your plant to grow into. Also the bigger the grow bag the more nutrients there will be in the soil purely because of the increased volume of soil.

A larger grow bag can also hold more moisture, meaning it will take longer for your plant to dry out. This can be a real problem with grow bags in hot greenhouses, they dry out really fast, a larger grow bag will slow this process down.

Large Grow Bag
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05/19/2022 12:11 am GMT

This monster bag is nearly 40 litres so gives lots of space for the roots of your plants to grow into. It is nearly twice as deep as regular grow bags and is what I have always used in my greenhouse for tomatoes and cucumbers.

What Plants Can I Grow In Grow Bags?

The answer is simple, anything you want, although some will do better than others.

Grow bags are traditionally used for certain crops such as Tomatoes and Cucumbers but in truth, anything will grow in there.

They are however expensive when compared to other grow methods and also usually take up a prime spot in the greenhouse or poly tunnel. Because of this, you want to grow a prized crop in there, such as your tomatoes or sweet peppers.

Most plants will grow just fine in a grow bag but root vegetables will struggle purely because of the lack of space. So don’t go growing potatoes, carrots, parsnips or other such root vegetables in grow bags.

How Many Tomato Plants Per Grow Bag

With one of the larger grow bags that I listed above I would suggest three large tomato plants per bag. If you have a skinnier grow bag then you might be better with two plants per bag.

If you think you can keep on top of watering, which will be every day in the height of summer, and feeding then go for three plants per bag.

Can You Use Tomato Cages In Grow Bags?

Yes, you can. Provided the circumference of the cage is smaller than the bag you can still stick it into the soil and it will work.

It will not be as sturdy as it would in a deeper bed as there just won’t be as much soil as usual to hold it in place. Normally though, especially with the deeper fill bags, there is just about enough room to hold a tomato cage upright.

How Many Cucumber Plants Per Grow Bag

This may be controversial with some growers as most suggest two plants per bag but I have always grown three plants per bag.

This way you are maximising your yield per bag and therefore getting more cucumbers for the same price. I can’t say I have ever had any problems with growing three plants per bag and I have no plans to change!

My cucumber setup
My cucumber setup

How Many Pepper Plants Per Grow Bag

Three plants per bag is best, is it just me or am I repeating myself? You can see a trend here, for me at least, three plants per bag is usually the optimum number.

When your grow bags are packed with thirsty plants like this though they are going to need plenty of watering so make sure you can water them every day in the height of summer.

If you can’t then one of these simple watering contraptions could be a lifesaver for you.

Designed For Grow Bags
Plant Halos 3x Pots Watering Tool For Grow Bags
£11.98
  • 3.1 Litre 'moat' with 6 watering spikes that delivers the water directly to the plants' roots
  • Water reservoir takes 3 to 6 hours before draining
  • Made from recycled, UV stabilised plastic and is guaranteed to last for 5 years


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05/19/2022 12:11 am GMT

Growing Potatoes in Bags

What we here in the UK call a grow bag and what our American cousins call a grow bag can be two different things. This can cause much confusion among beginner gardeners with google telling people they can grow potatoes in grow bags.

What is usually meant then this is stated on American focused websites is not really a grow bag as me and you know it but more what we would call a potato sack.

These sacks when filled with compost do make excellent growing mediums for potatoes, but regular slim grow bags do not, as there is just not enough room under the soil for the potatoes to form.

Perfect For Spuds
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05/19/2022 12:11 am GMT

Just remember that unlike grow bags these don’t come full of compost and you will have to provide your own. So just think about that when working out the cost of these bags.

What Else Can You Grow In Bags?

Any fruit or veg that isn’t a root vegetable will tend to well in a grow bag until you get up to larger fruiting trees and vines like grapes. There will not be enough room for the roots of these plants but everything in between will do well.

You also only really want to grow annual crops in grow bags as you will normally find you need to change the soil after a season of growth as most of the nutrients in the compost have been used up.

Salad crops can grow well in bags although in my mind this is a bit of a waste of the grow bag as they will grow equally well in any other spot. You have to remember that grow bags are a fairly expensive way to garden.

They should be treated as a prized spot and only given over to highly productive and sought after crops.

Some people also grow flowers in grow bags although I can’t say this is something I have ever done. Most flowers will do really well in grow bags though as they are usually packed with nutrients to aid the growth of fruit and veg.

If you are planning on a bit of a cut flower garden but don’t have the soil space then maybe grow bags might be a solution and allow you to have the cut flower garden of your dreams.