Growing Tomatoes in Grow Bags
March 26th, 2025 | Categories
Growing tomatoes in grow bags at home is a simple, convenient, and great way to grow fresh, juicy tomatoes at home. It’s a convenient, neat and effective choice for most garden situations, even for those with small gardens or patio gardens. The whole process of growing tomatoes at home from seed to harvest is remarkably simple and straightforward too, even for beginners. With the right care, a single tomato grow bag can yield an abundant summer harvest of tomatoes that you can eat fresh or use to make homemade tomato sauce.
One major advantage of grow bags is that they come pre-mixed with compost for growing in the bag, making setup easy. Typically, each bag supports three plants, which can produce hundreds of tomatoes in a single season. Grow bags are especially ideal for those with limited space or looking for an easy way to start gardening without changing or digging up swathes of the garden.
If you’re a beginner and wish to dip your toe in the water of growing your own tomatoes at home, then grow bags are perfect to start with. So, ready to get started? Follow our step-by-step guide below!
Why Grow Tomatoes at Home?
Tomatoes are simply delicious! They are one of the most popular, most eaten, vegetables around and growing them at home is just better! For instance, the tomatoes you buy in supermarkets are grown in soilless environments with artificial fertilisers injected into the plants to make them grow and produce. This is to guarantee yields, shelf-life and disease resistance year-round, and while this is perfectly safe, it comes at the expense of other qualities like flavour. They are also typically harvested before they are fully ripened. If you compare that to how they would grow naturally, the kind you’ll grow yourself, the flavour is night and day – the true taste of a tomato – and you can harvest when they are fully ripe and ready to go.
Additionally, homegrown tomatoes are healthier for us with higher levels of the pigment ‘Lycopene’. Lycopene has been shown to help unclog blocked arteries and is thought to be a factor why the Mediterranean diet is so healthy.
There’s more; you can save money. Buying tomatoes regularly is quite expensive. But a single plant can produce hundreds of tomatoes in a single season, so it can pay for itself many times over. You can even save the seeds from your tomatoes and grow them again next year too.
Plus, it’s fun! The journey of growing your own produce can be very rewarding giving a sense of achievement. There are many different varieties of tomato you can grow that you never see in the shops from very sweet cherry tomatoes, to plum, to super-sized full-flavoured beef tomatoes.
How to Grow Tomatoes in Grow Bags at Home
To grow tomatoes successfully in grow bags it pays to be prepared, and know the nuances of bag growing, so you can maximise your harvest while minimising any issues and effort.
Something to note; in doing your own research you may come across the terms ‘bush/determinate’ and ‘cordon/indeterminate’. This refers to the type of tomato plant. Bush or determinate types grow like a bush, more outwards than upwards, and are not well-suited for grow bags. Cordon or indeterminate, grow upwards – over two metres – and are what many people would conder the classic type of tomato plant you see with supporting stakes. These are suitable for grow bags and are what we will be referring to throughout these steps.
If growing your cordon tomatoes from seed, there are a few more steps to consider before potting and transferring to the grow bag which we will cover below. If buying young tomato plants, you are already at the stage to get stuck in and plant in the grow bag.
Growing Under Cover for Success
Sadly, in most places in the UK, the summer weather isn’t consistently sunny or warm enough for tomatoes to grow outdoors. So that means a greenhouse or a growhouse is an essential item for success when you’re at the stage of planting in the grow bag. If you don’t have a greenhouse, then a growhouse is a cheaper but just as effective option, especially ones that are designed to accommodate taller plants. Just be sure to place in a sunny spot against a wall or fence, and when the growing season is over to dismantle it so it doesn’t break in stormy winter weather.
Growing from Seed
The best time to sow your tomato seeds will be from March to April. Sowing can be done earlier even in January, if growing in a greenhouse or on a warm windowsill with a heat mat or heated propagator. This will give them the right protection and help with the conditions needed to germinate. Be aware though, that seeds need somewhere warm to germinate so ensuring a consistent daytime temperature around 20°C to 25°C and night-time temperature no less than 15°C is essential. The heat mat or heated propagator will ensure you can start growing from seed early in the year. Otherwise, best to wait until the ambient temperatures are a bit warmer.
When sowing, use a seed growing tray with cells to make it easier to space the seeds out. If using a heated propagator, these typically don’t have cells, so make sure each seed has a good amount of space. Think about how many plants you want too. If you’re only growing a few plants, sow three to five seeds (each plant can produce hundreds of tomatoes) into your seed tray or propagator, pre-prepared with a good quality vegetable compost. After this, cover again with a thin layer of compost and water lightly. If you want to ensure you have a good number of plants, sow a few more seeds than you want plants, to allow for some losses, and so you can select the strongest seedlings later.
After roughly a week the seeds will have started to germinate – if you see that they have two true leaves and are sprouting up they’re doing well – how exciting! At this point, place somewhere with plenty of light and at the same temperature range if not already. Typically, they will need feeding from about the fourth true leaf stage, especially if you have used seed compost to pot them up (it is usually lower in nutrients than using a vegetable compost). To feed, use a high potash tomato feed. If you see the bottom leaves start to turn yellow or purple, this can be a sign that they are running out of nutrients (purplish tints can also be due to low temperature).
With all your feeding and care the plants will grow quickly and when they are roughly 15cm tall it’s time to get ready to transfer the young plants out of the container to larger pots. If you already had them in pots, then you don’t need to prepare to transfer them anywhere at this stage unless you used a large single pot for the seedlings, in which case now might be a good time to transfer to individual pots to avoid them crowding one another.
Fill your pot with compost and then dig out a hole for the young plants. The hole needs to be deep enough to plant without curling the roots. Then, carefully dig the plants out of the container, if the soil holds together nicely by the root network (it doesn’t fall apart) then they are good to go. When transferring, place them gently without firming them in. Support any stems if necessary, by tying them to a small pea or bamboo stick and give them a light watering too using a fine watering can rose.
Growing from Young Plants
If you aren’t keen on growing seedlings yourself then buying young tomato plants will do the job just fine, and are available to purchase from any Squire’s later in spring.
What You Will Need
Preparation is key! Gather these essentials before starting:
- Tomato grow bag: One large bag can accommodate three cordon-type plants.
- Tomato seeds or young plants (x3): Seeds allow for variety selection, while young plants save time.
- Sharp knife or scissors: For cutting the bag and trimming plants.
- Hand fork and trowel: To loosen and move compost.
- Growing pot/halo/ring (optional): Helps direct water to roots.
- Stakes (e.g., bamboo canes): Supports the plants as they grow.
Setting Up Your Grow Bag
A few things to consider when placing your grow bag and getting it ready.
Choosing the Right Location
Tomatoes thrive in warm, sunny locations. Place your growhouse and grow bag in a spot with maximum sunlight in the garden, preferably against a wall or fence for shelter.
Preparing the Growbag for Planting
- Give the young plants a good watering in their pots before transferring.
- Shake the bag to aerate and loosen the compost. Don’t be scared to get physical!
- Set the growbag flat in the greenhouse or growhouse, and cut the planting holes (usually marked on the bag).
- Once cut, use the hand fork to break up any compacted compost.
- Poke drainage holes along the bag’s sides and bottom too as drainage is crucial.
Planting Your Tomato Plants
Now for the exciting bit, planting! There are a few different ways of planting in.
Option 1: Planting Directly into Compost
- Dig a hole deep enough for your plant.
- Remove the plant from its pot, trim lower leaves, and loosen roots.
- Place in the hole, replace compost, and pat gently but do not firm the compost too much.
Option 2: Planting Inside Thin Plastic Pots
- Transfer plants into thin plastic pots if not already in one.
- Cut the base off to allow roots to extend into the compost in the grow bag.
- Dig a spot, place the pot inside and firm it in gently.
Option 3: Using Grow Pots/Halos
- Push the grow pot into the compost before planting.
- Remove some compost to make space.
- Plant the tomato inside, replace the compost and firm gently.
Supporting Your Tomato Plants
Since cordon tomatoes grow tall, they need support:
- Place a bamboo cane behind each plant.
- Use twine to tie the stem to the stake as it grows.
- You can use one, two, or three stakes per plant based on height.
Watering & Feeding
Tomatoes require consistent watering to prevent fruit splitting and blossom end rot. Follow these tips:
- Water little and often to maintain moisture levels.
- Avoid waterlogging by ensuring proper drainage.
- On hot days, water multiple times.
- Once flowering starts, feed weekly with high-potash fertilizer.
Pruning & Ongoing Care
Pruning is necessary to control growth and improve fruit production:
- Stopping: Once the plant has four or five trusses (flower stems), trim the top to focus growth on fruit.
- Pinching out: Remove small side shoots that grow between the main stem and trusses.
- Leaf removal: Once fruit appears, strip lower leaves to improve airflow and prevent disease.
Common Issues & Solutions
- Tomato Blight
- A disease causing tomato and foliage rot, often due to damp conditions.
- Improve ventilation and keep soil well-draining.
- Less common in greenhouse-grown tomatoes.
- Fruit Problems
- Blossom End Rot (dark patch on tomatoes) and Splitting Fruit occur due to irregular watering.
- Blossom Drop (flowers falling off) also results from inconsistent watering.
- Pests
- Common pests include greenfly, whitefly, and aphids.
- Use natural repellents like companion planting marigolds or commercial repellents as needed.
Harvesting Your Tomatoes
Congratulations on getting to this stage because you’ve successfully grown your own tomatoes from a grow bag! Pick the fruit when they are ripe. Different varieties will grow and ripen at different times, and tomatoes on the same plant can also naturally ripen at different times too. To know when they are ripe and harvest, be sure to know the specific signals for your tomatoes, typically a colour and firmness change. Start picking at this stage.
Wrapping Up
There you have it. Soon you’ll be well on your way to growing your own plentiful harvest of deliciously fresh tomatoes at home in grow bags. You will notice the difference in flavour right away, they will be nothing like your typical store-bought tomatoes. Your plants will, unfortunately, die when the first frosts set in, which is a shame, but if you’d like to save the seeds for next season you can.
