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15 Mistakes Even the Most Experienced Tomato Gardeners Can Make

*This article was updated on April 8, 2021.

Tomatoes are one of the most popular plants to grow in home gardens.

They’re a useful and delicious crop, and growing them can bring a range of rewards, including jealous neighbors who want to know who you grew those monster beefsteaks.

Often, they’re relatively easy to grow and can be abundantly productive. But I’ve also seen plenty of mistakes that make the whole process harder than it needs to be.

Let’s look at the 15 common mistakes people make when growing tomatoes.

This list will be your secret weapon for growing and enjoying an abundant tomato harvest year after year.

1. Growing the Wrong Varieties

First of all, it’s important that you choose the right tomatoes to grow.

Think about your climate, microclimate, soil and growing conditions when choosing a tomato variety. You’ll also need to think about what you want to do with your tomatoes.

Are you going to make caprese salad and tomato sandwiches all summer long?

Are you planning on canning homemade salsa or sauce?

Think about the characteristics of the different tomato varieties you’re considering. For example:

  • Whether the seeds are heirloom tomatoes (and will allow you to save seeds and grow more plants next year) or hybrid types (which will not come true from seed but may have better pest or disease resistance). 
  • The growing habit of the tomatoes (determinate or indeterminate), vining or bush varieties etc.
  • The size and type of fruit, and what these tomatoes are best used for. How will you want to use the tomatoes you choose.
  • How long does it take for your chose variety to mature? Fast-fruiting varieties are usually best for shorter growing seasons. 

2. Not Providing the Right Conditions for Strong Seedlings

Whichever seeds you choose, it’s important to create ideal conditions for seed germination. The best germination rates are achieved with temperatures between 60-85 degrees.

In short seasons, it’s best to sow indoors, undercover, before transplanting seedlings to their final growing positions once the weather has warmed. 

I sow tomato seeds, along with other warm-season crops like peppers in January or February indoors. This is one of the earliest sowing jobs of the year. These are planted in my polytunnel in late April or early May (depending on the weather) most years. 

Lack of natural sunlight is one of the biggest barriers to growing tomatoes indoors in areas that experience very short days in the winter. Seedlings without enough light can get leggy, and weak. 

It’s important to choose as sunny a spot as possible in which to grow them. But plants may still need an extra helping hand.

LED grow lights can be useful, and or foil to reflect the light. You should also turn seedlings regularly to prevent them from leaning towards the light. 

Of course, there are other conditions that need to be met. You’ll also need to choose the right growing medium, water well, and provide the right temperatures. But getting the light right is the thing that is often overlooked. 

3. Not Potting Up Tomato Plants in Time

When you grow tomato plants indoors, and whenever you don’t direct sow them, it’s important to think about when they must be moved to larger containers.

Leaving tomatoes, closely spaced in seed trays, or letting them outgrow their individual pots, can often cause a range of problems. 

Tomatoes left too long in seed trays can face too much competition and become stunted. Tomatoes in small pots can become root bound, and can prematurely flower if they’re left too long in their pots.

Remember, tomatoes can be buried slightly lower in the top when potting up. New roots will form along the newly covered stem section and make for healthier, sturdier plants. 

4. Forgetting To Harden Off Plants Grown Indoors

If you’re sowing tomatoes indoors to plant out later, another important thing to remember is you need to harden them off before placing them outdoors. 

Hardening off involves gradually acclimatizing plants to outdoors conditions. If you omit this stage, the shock of transplantation may stunt or even kill your tomato plants. 

5. Planting Tomato Plants Out Too Early

Don’t be tempted to plant tomato plants out too early. Getting the timings right is crucial in gardening and this is particularly true when it comes to warm season plants like tomatoes.

I’ve known gardeners to rush to plant everything out when the first sunny, warm day in spring arrives. But it is important to be absolutely certain that the frosts have passed and warm weather lies ahead before you risk planting out your tomato plants. 

6. Putting Tomato Plants in the Wrong Places

There are a range of different places where you can grow tomatoes. You can grow them, as I do, in a covered growing area (greenhouse or polytunnel). You can also grow them outdoors, either in containers, in raised beds or in the ground. 

But while there’re plenty of places that will be perfect for growing tomatoes, there are also plenty of places that aren’t ideal.

It’s important to take the basics of climate, conditions, soil etc. into account. Think about sunlight and find an area of full sun. Make sure your tomatoes aren’t in a particularly exposed location or they may be damaged by strong winds. 

If you’re growing in containers, choose ones that are large enough to accommodate your plants. Make sure, wherever you grow tomatoes, that their needs are met.

Don’t plant them too close to other plants, or to each other.

7. Not Staking Tomato Plants

Some tomato plants can support themselves. But most need some form of support as they grow if you are to get the best from them.

Check out this article on supports for tomato plants to get some suggestions about which option to consider, and for tips on making your own from things that might be readily available to you where you live. 

8. Not Taking Advantage of Companion Plants

By planting tomatoes alongside a range of other plants, you can take advantage of the beneficial interactions between them.

Companion plants around your tomato plants help increase their yield and get you the best possible results. 

Borage, marigolds, basil and nasturtiums are common tomato companion plants, but you can see our entire list of veggies, herbs and flowers that benefit tomatoes here.

There are also a number of plants that shouldn’t grow anywhere near your tomatoes.

9. Improper Watering

One of the easiest ways to go wrong in a garden is to give your plants too much water. It’s important to understand how much water tomatoes require on average. But also how those requirements differ over the course of their growth period.

Watering is crucial during the flowering and fruiting stage.

But adding too much water at the fruiting stage can cause fruits to split, or increase the risk of disease. It’s also a good idea to reduce or stop watering at the end of the season. This can increase the number of mature fruits you get. 

Similarly, it’s important not to stress tomatoes by letting them dry out too frequently. Most tomatoes do best with about 1-2 inches of water a week.

Avoid watering tomatoes from above. It’s best to water tomato plants at the base. Water resting on foliage increases the risk of diseases, and sometimes causes scorching in the hot sun. 

10. Not Fertilizing or Using the Wrong Type of Fertilizer

You’d be surprised by how many people just stick tomato plants in the ground or in containers, and expect the soil and sunshine to deliver what they need.

Tomatoes are relatively ‘hungry’ plants, and they need extra nutrients, especially during the flowering and fruiting period to achieve the best harvests possible. 

I use a comfrey liquid feed in addition to adding slow-release fertilizers in the form of mulch (see below). 

Related Reading: My Homemade Tomato Fertilizer Recipe Perfected Over 30+ Years

But when using fertilizers on your tomatoes, it’s important to realize not all fertilizers are perfect for tomato plants.

Tomato plants need plenty of nitrogen, especially during the early stages of their growth. But adding a general purpose, nitrogen rich fertilizer to tomato plants when they’re flowering and fruiting can do more harm than good. 

Adding too much nitrogen can encourage plants to put too much energy into putting on green, leafy growth rather than fruit.

11. Not Mulching, or Choosing the Wrong Mulch for Tomato Plants

Chopped comfrey leaves make a great tomato plant mulch

Adding a mulch around tomato plants is crucial for maximising yield and getting the best results possible. Mulches act as slow-release fertilizers, build and improve the soil over time, help retain soil moisture and protect the soil surface. 

But it’s important to use the right mulch.

The nitrogen issue described above comes into play when it comes to the mulch you use around tomato plants. Avoid nitrogen-dominated mulches like grass clippings and opt instead for a mulch of comfrey, good quality compost or another more balanced mix. 

12. Not Dealing With Tomato Pests and Diseases In a Timely Fashion

In an organic garden, the best way to deal with pests is wholistically. By creating biodiverse ecosystems, with plenty of plants and beneficial wildlife, we can keep things in balance.

This reduces the incidence of pest problems. But there are still certain to be times when you encounter tomato pests.

Take a look at our article documenting twenty of the most common tomato plant pests and how to deal with them.  

Prevention is always better than cure. But tomato plants can often also suffer from a range of diseases.

How severe a problem a disease will be will depend, of course, on what type of disease you’re facing and how healthy and vigorous your plants were to begin with.

Keep tomatoes as healthy as possible, and maintain good hygiene and environmental conditions, and disease is less likely to take hold. 

But when disease does strike, it’s important to stay on top of things. Often, all you can do is remove affected foliage or fruits as soon as possible.

By remaining vigilant and acting at the first hint of a problem, it is often possible to prevent its spread. 

13. Not Pruning Tomato Plants For Optimal Harvests

Pruning tomatoes is a great to get the best possible yield.

Here’s our step-by-step guide to pruning tomatoes with photos.

And once you’ve pruned your plant – don’t throw those plant sections away! Use them to clone new tomato plants from cuttings.

14. Not Ripening Green Tomatoes Late in the Season

Pruning also plays a role later in the season. As the first frost rapidly approaches, there are a number of things that you can do to make sure green tomatoes ripen as quickly as possible.

Take a look at our article to find out more about how to get green tomatoes to ripen.

By taking the measures described in that article, you can make sure you get as many ripe tomatoes as possible before time runs out this year. 

15. Letting Tomatoes Go To Waste

But remember, you can use those green tomatoes too. In this article you’ll find tips on what to do to make the most of them. 

When you have a glut of a particular fruit or vegetable, it’s easy to feel overwhelmed, and wonder what to do with them all. Fortunately, there are plenty of ways to use up your tomatoes – no matter how many you have.

You can preserve your tomatoes with canning methods, by drying them, or by turning them into interesting preserves to last you through the rest of the year.