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5 common Tomato Growing Mistakes (and how to avoid them!)

Written by Sarah Talbot

Tomato plants are often one of the first plants you try as a child.  But despite a lifetime of growing them its easy to make some of these tomato growing mistakes. Not to worry, there are a few simple changes you can make to ensure you get a big crop from your tomato plants. 

The top 5 mistakes people make when planting tomatoes are the same regardless of whether you are growing tomatoes in pots, in a greenhouse or outside in the garden. 

How many are you guilty of?

1) Planting Tomato seeds too early

2) Not planting tomato seedlings deep enough

3) Not supporting tomato plants well enough 

4) Planting tomatoes in the same place every year

5) Inconsistent watering

1)  Planting tomato seeds too Early


Tomato plants like warmth - both from the air and the soil. One of the first mistakes that new gardeners make is to plant their tomato seeds too early.  This means that the seeds not only lack the warmth they need but also the light.  This will lead to them becoming etoilated.  A fancy term for being pale, drawn out and generally pretty weak.  

So, avoid the temptation to both plant your seeds too early, and plant your young plants out where they will be prone to frost damage. 

When to Sow Tomato Seeds


Sow from late February to mid-March if you are growing your crop in a greenhouse or Grower Frame plant house, or from late March to early April you are growing outside. 

Soil warming - when to plant Tomato Plants

It takes a good 7 -10 days of 21° C ( 70°) daytime temperatures to warm the soil. You can speed this up by covering the soil a few weeks before planting with a Eco-Green Fleece Blanket or Easy Fleece or Poly tunnel. 

one way to judge it is to wait until night time temps stay in the 10°C (50° F) range before planting tomato plants out.

If you have already planted and your tomato seedlings are leggy, then try and give them as much light as possible.  Move them to the brightest windowsill you have, remove net curtains and turn then regularly so they don't have to seek the light.  Even consider putting something reflective behind them like tinfoil to reflect the light back at them.   

2) Planting tomato Plants too Shallow

Tomatoes need to be planted deep.

Haxnicks Vintage Ash Hand fork planting tomatoes

When transplanting most plants it is important to plant them at the same level they were in their pot.  Not so for tomato plants - tomato seedlings form additional roots all along any buried parts of the stem. This gives healthier tomato plants less susceptible to drought, pests and tomato diseases. 

These are called Adventitious roots.  They form from nonroot tissue and are produced both during normal development for example the nodal roots on strawberry plants and as a response to stress, such as lack of nutrients, too much watrer or damage to the plant. 

If you look closely before planting you will see tiny bumps along the stem.  These are where the new "adventitious roots" will grow from. So, planting tomato plants deep means extra roots, a more stable plant and an increased ability to take in water and nutrients.  

The Deep Hole Method

One way to do this is to dig a hole deep enough so that the tomato plant is buried up to just under the top-most set of leaves.

This feels a little extreme though so most people opt to plant the tomato plants up to just above their bottom-most set of healthy leaves. Some people remove these leaves before planting whilst some leave them.  As well as growing the extra roots this allows the plant to access water farther down in the soil straight away giving it a good start.  

How deep to plant tomatoes

Dig the hole as deep as needed to accommodate the root ball and most of the stem - around 20-25cm (8-10"). Loosen the roots a little and then drop the seedling in the hole and fill with soil mixed with good quality compost.

3) Not Supporting Tomato Plants properly

This is a very common tomato planting mistake. Tomato plants are large and heavy, especially when they are cropping.  So plant support will be needed.  And they need to be put in before the plant.  Instead, people leave it after the plant is in or even worse, until the plant is out of control.   

Why do you need plant supports? 

Haxnicks Tomato planter with plant support frame for growing tomatoes

Even if you add supports as soon as the seedling is planted out, driving supports into the ground at this point can easily damage the plants or roots.  You will most likely compact the soil around the roots as you are clomping around too!  This stunts the tomato plants' growth as it makes it harder for the plant to access water and nutrients.

If you wait to add support until the plant is larger - and really looks like it needs support - then you risk wind damage from plants falling over and branches breaking off.

Tomato plant supports

Haxnicks Tomato Crop Booster Frame plant support for growing tomatoes

You can use bamboo canes driven into the ground or special planters that come with in built supports such as the Climbing tomato planter which includes a frame or Tomato Patio Planters which have pockets to hold canes and keep your plant supported. 

If you really want to support your tomatoes then the Tomato Crop Booster Frame is ideal for both growing in pots and the ground.  It has support bars that can be edged up as the plant grows and support the heavy branches to give an increased yield.   

4) Using the Same planting spot each year

Planting in the same place and not practicing crop rotation can cause problems.  Many diseases live in the soil so planting the same crop in the same place can cause re-infection.  Added to this, tomato plants are heavy feeders and heavily deplete the resources from the soil so any area of the garden where tomatoes have been grown needs to recover. 

Planting Tomato plants in the garden  The main tomato diseases are blossom-end rot and tomato blight, both the result of soil problems. Blossom rot is caused by a deficiency of calcium in the soil. And blight spores can stay in the soil and destroy crops for multiple years.

Rotating where you plant the crops in your vegetable garden can help reduce the effects of diseases.    

As a rule of thumb, only return tomatoes to the same spot every 4 years.  

Growing Tomatoes in pots and planters

If you are growing tomatoes in pots, planters or containers then make sure to clean them thoroughly as soon as the tomato harvest is over. Especially if you have had blight on your tomato crop. 

Haxnicks tomato planter for growing tomatoes

If you are happy using bleach then use one part unscented household bleach and nine parts water. Or if not, fill a bucket with a mixture of one part white vinegar to four or five parts hot water and clean the pots with this. Then dry and store. If you are using a Vigoroot Tomato Planter then you can wash by hand or even put it in the washing machine on a cold wash.  

It is always better not to let tomato leaves or branches touch the ground anyway to prevent diseases.  If you are putting the pots back in the same spot on the patio though then ensure that all plant material is removed and give it a good was down too. 

5) Inconsistent Watering 

Last but definitely not least, tomato plants should not be over or under watered.  This is probably the hardest mistake to put right especially if you are gardening on an allotment so can't be there 24/7 to cater to your needy tomatoes. 

Both over and under watering can cause fruit to split which in turn can allow diseases to take hold.

split cherry tomato home grown

Avoid dehydration by mulching around the tomato plants.  Without it plants' roots can rapidly dry out. Mulch also helps to regulate the soil temperature, keeping it constant despite the weather and keeps weeds at bay that would compete with the tomato plants.

Use a  5-10cm (2-4″) thick layer of straw, shredded leaves or compost to help insulate and protect plants.  

How to Water Tomatoes

Vigoroot Pot and Haxnicks Water saucer for growing tomatoes form seed

The saying is "Water slowly, water deeply"  Don't flood tomatoes but use a drip hose if possible to provide the water slowly to the plants. Water regularly directly to the roots rather than from above.  Watering from above can spread disease and pests faster and wastes water through evaporation.

 If watering is a problem then look for self watering solutions like the Water Saucer or for bush tomatoes, the Self Watering Tower Garden. These will allow the tomato plants to help themselves as and when they need it and are also an effective way of delivering plant food to the growing plant.    

I hope that this has given you some help in avoiding these tomato growing mistakes.  Happy Tomato Growing!




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