Read more

What Is The Best Grow Bag Size For Tomatoes?

What is The Best Grow Bag Size For Tomatoes?

To any person who is getting into gardening, I recommend two plants to start with – radishes and tomatoes! Radishes – because they are fast and provide a nearly instant reward – and rewards make a hobby addictive. So that first salad with your first radish is always great.

However, tomatoes take quite a bit longer, but wow they are worth it! A fresh homegrown tomato always tastes infinitely better than a shop tomato. If you do not have an actual garden, you can always grow a tomato in a pot or even a grow bag. What is the best grow bag size for tomatoes? This will depend on a few factors, let us have a look at these.

A Quick Overview Of Tomatoes

I can write a lot about tomatoes, but there is one fundamental thing you must understand about them. They are very diverse! Rules that apply to one cultivar of tomato do not apply to all others. The most important thing to understand about tomatoes is that they are broadly categorized into two groups based on growth style.

Indeterminate Tomatoes

These tomatoes grow in a rambling style and the vines flower and shoot and produce fruit throughout the season. An indeterminate tomato can take over your entire garden, or if you try and grow one in a pot or grow bag – they can take over the patio! They require heavy pruning if you wish to grow them in a pot or grow bag.

Determinate Tomatoes

Determinate tomatoes grow to a specific size, flower, and fruit and then often die after this. Sometimes if you are lucky you get a second flush of fruit out of a determinate tomato but normally not. Determinate tomatoes are always my choice for growing in pots as they are not too likely to get out of hand and take over your life. When searching for tomato seeds, get determinate ones for your to-grow bags.

Italian tomatoes just taste good because well – Italians (in Italy life is too short to eat bad vegetables. If you are growing in small bags and are very space limited, one of these dwarf patio varieties can be useful.

Check Price on Amazon

I have not grown that specific cultivar, but have grown yellow pear dwarfs that were very similar. Yellow tomatoes tend to have a bit less acid in them – so if you grow a few plants this minimizes the risk of you turning your stomach upside down. Commonly, we grow tomatoes, then they taste so good we eat too many from the vine (tomatoes straight from the vine are the best). This can then lead to a need to stay very very close to the toilet for a day or two and not drive on bumpy roads.

What is a Grow Bag?

Broadly speaking grow bags are any bag that can hold soil or growth medium for growing plants. In this article, we will specifically refer to grow bags made from a porous material. These bags have advantages with drainage and aeration that can be beneficial for growing tomatoes in certain environments. If you wish to grow in a non-porous grow bag, the rules for such bags and normal pots are about the same. These do not fit in the scope of this article. This article deals with the choice of porous grow bags, specifically answering the question “What Is The Best Grow Bag Size For Tomatoes?”

Here is an excellent example of a simply grow bag similar to the ones I have used.

Check Price on Amazon

The Best Grow Bag Size For Tomatoes

The best grow bag size for tomatoes should have the following features:

  • Space

Tomatoes can have quite deep roots. When we look at the function of roots they are there to help a plant scrounge nutrients from the soil. The more soil the plants have access to, the more trace nutrients they will be able to find. Many commercial tomatoes are grown on the bare minimum of soil and hence the taste of the fruit is bland and low in nutrition. We, as home growers, want to taste healthy, so my advice is always to try to get a bigger bag.

  • Air circulation

Tomatoes need to have plenty of air circulation.  In this regard, a bigger bag allows you to build a support structure that can hold your tomato up and enable air circulation.

  • Good drainage

Bigger bags make it easier to ensure good drainage. You can always place a bit of gravel at the base of a grow bag to augment drainage if you live in an area with very high rainfall.

  • Suggested bag sizes

I would suggest a minimum of a 5-gallon bag, but a 10-gallon bag is probably going to be better if you have enough space. If you are gardening on a balcony also be aware of the mass you are adding to the balcony – you would not want it to fall off the building because you put ten huge grow bags and then it rained and they got heavy and overburdened the structure!


How To Choose The Best Grow Bag For Tomatoes?

A really important consideration with grow bags is surface area to volume ratio. If you take a small grow bag, the surface area of the grow bag is high, and the volume is low – this means that there will be a lot of evapouration out of the surface of the bag, and in hot dry weather, you can end up with your soil drying very fast. If the water you irrigate with has high dissolved solids (salts) then you can end up with your soil becoming saline from this high rate of drying.

In my garden I mainly irrigate with rain water that I harvest from the road outside and store in a reservoir. This water has a very low salt content and hence salt build up in the soil is of little worry. I can, if I wish, use a small grow bag without the risk of too much salt build up.

In most cases however, using a bigger bag reduces the surface area to volume ratio – this means that there will be less loss of moisture from the bag surface to the atmosphere. 

This is one of the reasons I would choose a 10 gallon grow bag over a 5 gallon grow bag. The 10 gallon will dry out somewhat more slowly, and still provide plenty of aeration for your tomato plants.

What Is The Best Grow Bag Size For Tomatoes? My advice would be to try for a minimum of 5 gallons but if you can use a 15 or even 20 gallon bag, go for that. The fruit will taste better.

What Are The Different Types Of Grow Bags?

I find it easiest to break the bags down into ones made from synthetic compounds, and ones made from natural compounds. 

Synthetic grow bags

Various synthetic plastic materials are used to make non-woven fabrics. These are normally bonded together with some sort of heat process to produce a tough plastic material that will give years of service life. There is a risk of these bags shedding microplastics into your soil – this is a matter of increasing concern globally.

Bamboo and jute grow bags

Natural grows bags are an eco-friendly option. They can be used for both indoor and outdoor plants. They are durable and sturdy but will not last as long as a synthetic bag. The main benefit of these bags is that you do not need to worry about any microplastics entering your soil, or any plasticizers leaching into your soil. Consequenly, they represent a safer option for your garden in the longer term.

Soil and Amendments

If you are going to invest money in grow bags, make sure to use a decent soil.

Check Price on Amazon

With tomatoes they are heavy feeders so if you want to make them taste really good you can add a bit of azomite or similar micronutrient rich material.

Check Price on Amazon

I would recommend, and I know this sounds a bit weird, but never under estimate the power of human pee as a fertilizer for tomatoes. It is free, readily available and one of their favorite nutrients – in moderation. Once a week.

I also give my tomatoes a lot of chicken, goat and cow manure. If you can find a horse, get some dry horse manure and fill a 5 gallon bucket. Soak the manure for three days in water. Strain the solution and you get a nice black liquid manure tea that also works wonders with your tomatoes.

For supplemental feeding you can also get a bag of slow release organic fertilizer such as this.

Check Price on Amazon

You will notice I always recommend organic fertilizers where I can. This is based on logic – it costs about the same amount of money to grow organic vegetables as it costs to grow ones that are fed chemical feeds, and hydroponics is more expensive. I find that when I grow organic food it just tastes better – so for me, taste, and health are important motivators for my gardening.

I do not know whether some of these chemical products out there can cause harm in the long term – in my life I have seen many things that were “as safe as water” get reclassified as carcinogens, so I use the precautionary principle. If you can do things in a safe, old fashioned tried and tested way – organically – why introduce variables that could expose you to risk?

In Conclusion

Grow bags provide a useful tool for us to grow tomatoes in a well drained, breathable container that can in certain environments produce excellent results. If you live in a humid area, where the rate of evaporation off the surface will not be that great, these bags are a perfect way to get your soil moisture stable and provide breathable conditions for the tomato roots. If however you are in a hot dry environment with low humidity, you may find that these bags will give you problems – especially with salt build up.

I have found that in high mountains the grow bags just do not work as the evaporation rate is too high due to the low atmospheric pressure. My general advice is with grow bags bigger is better – big bags give you more space for the roots of the plants to search out yummy micronutrients. These micronutrients make the difference between a bland insipid shop tomato that provides mere decoration on your plate and a home grown tomato masterpiece that nourishes your body and soul.

What size container is best for growing tomatoes?

Frequently Asked Questions

How many tomatoes can I grow in a 15-gallon bag?

I would plant no more than two plants. In reality, a single plant can be fine for this size grow bag, but if you plant two, you can kill the weaker one once they start growing faster. This minimises your risk of having a bad tomato hog an entire bag for a season. You can expect a large crop of such a grow bag, if you grow the right tomato cultivar. This will depend on your area, but I would be rather disappointed if I did not get 10 pounds of tomatoes out of a 15 gallon grow bag in a season, and would, with a bit of effort expect 15 pounds or more. If you grow a heavy yielding variety such as Heintz, expect way more than that.

Are grow bags deep enough for tomatoes?

Yes. Tomatos can in fact grow in very small bags - most commercial tomatoes are in fact grown in bags that are about 6- 8 inches deep. This however produces bland insipid fruit. If you have a deeper soil, the roots can scrounge around in it for micronutrients that make the fruit taste better. Hence a 5 gallon grow bag is about the minimum you should consider, and a 15 or 20 gallon bag is better.

What size container is best for growing tomatoes?

5 gallon bags are about the smallest I would consider, with a 15 or 20 gallon being better. In a 20 gallon bag you can grow two decent sized plants. In the smaller bags I would plant two plants and kill the weakest after a few weeks. This ensures your bag will produce optimally.

What size grows bag for tomatoes?

The minimum size you shoud consider is a 5 gallon bag, with a 15 or 20 gallon bag being a better choice.