10 Things You Should Never Do When Growing Tomatoes in Containers

You don’t need a huge garden to harvest an abundance of tomatoes. Compact bush (determinate) varieties are perfect for growing in containers, pots, or grow bags. Proper sizing, soil, drainage, and maintenance are crucial for keeping these plants small and productive. 

However, there are some things you should never do when growing tomatoes in containers. If you avoid these ten container gardening mistakes, you’ll save yourself many headaches and enjoy epic tomato yields.

What are the Biggest Container Tomato Mistakes?

Improper watering is one of the biggest mistakes that beginners make when growing tomatoes in containers. Potted plants need more water than their counterparts. Less soil volume in the container means that the soil dries out faster. However, the smaller space also means it is easy to overwater, causing soggy anaerobic conditions that can lead to root rot. 

A balance of drainage and consistency is crucial. Grow your tomatoes in large containers with drainage holes and quality compost-rich soil. Check the moisture level every other day in hot weather, and aim to keep the soil about the wetness of a wrung-out sponge. 

10 Things to Avoid with Container Tomatoes

Growing tomatoes in containers is very straightforward. Just like growing in raised beds or in the ground, your plants will need full sunlight, well-drained soil, balanced fertilizer, and consistent moisture. Proper spacing, container size, pruning, and trellising are also crucial for success. 

Tomatoes can grow quite large and yield in abundance, but they must have the proper conditions to thrive. Avoid these common mistakes for epic tomato yields from a container:

Insufficient Container Size

Successful potted tomatoes require the right-sized container. Tomatoes can grow roots two feet deep and wide or more! A small pot will not provide enough space for these plants to thrive. Moreover, a tiny pot can topple over from the weight of a heavily fruiting plant.

Grow your tomato plants in pots at least 10 gallons, ideally 15-20 gallons. This translates to an 18-24 inch diameter pot. When in doubt, choose the largest pot possible. Fabric pots are a great way to maximize space and soil volume while minimizing weight. Try a 15 gallon or larger grow bag, or opt for a small raised bed to grow several tomatoes in one place. 

Problems With Small Pots

A small pot also lacks sufficient soil volume to hold onto water during the hottest months. Tomatoes require plenty of moisture and are very prone to drying out while growing in containers. If you plant them in a small container, the soil may dry out quickly, and the roots can start winding around in circles. 

Rootbinding is a common problem with potted plants that leads to stunting and poor fruit production. Plants growing in small plastic pots are the most prone to rootbinding. Prevent rootbinding by growing in large, porous earthen or fabric pots that naturally “air prune” the roots. When the roots hit above-ground oxygen, they naturally stop growing.

Too Much Nitrogen

We know tomato plants are heavy feeders, but there can be too much of a good thing. Overfertilizing with nitrogen is a common mistake. Excessive amounts of nitrogen cause tomato plants to produce a larger volume of leafy growth. This focus on foliar overgrowth detracts from fruit production. As the plant channels its energy into loads of leaves and stems, it may fail to produce flowers or fruit. 

The easiest way to avoid this mistake is to use a balanced, slow-release fertilizer. Balanced fertilizer means that the NPK ratios are close together. For example, 4-4-4 or 3-4-6. The latter is particularly advantageous because it has higher amounts of potassium and lower amounts of nitrogen. Tomatoes still need nitrogen, but they should not be overfed with it.

Slow-release means that the fertilizer gradually feeds the plant over time. Organic fertilizers are always slow-release because they require beneficial soil microorganisms to mineralize the ingredients. As the organic ingredients are transformed by microbes, they become available to plants. The result is long-lasting fertility that slowly becomes available to tomato roots throughout the season.

Avoid Synthetic Fertilizers 

It’s best to avoid quick-release synthetic fertilizers because these products pose the most risk for overfertilizing. Quick-release nitrates add a mega dose of nitrogen to the soil all at once. These synthetic ingredients bypass the microbial “digestive system” of the soil. Instead, they funnel a big blast of nutrients to the roots. 

Home gardeners are particularly prone to overfertilizing with synthetic products. An excess of nitrates can also have detrimental effects on waterways, soil quality, and pest infestations. Because the plants receive a spike of fertilizer all at once, they require repeated applications that may imbalance the soil mineral profile and reduce overall yields.

Too Much Water

Proper irrigation is essential for all tomatoes, but especially for those growing in containers. Too much water can rapidly harm potted plant health because the water has nowhere to go. As a result, it accumulates in the bottom of the pot, creating conditions amenable to root rot, a major disease of tomatoes and many other plants. It is caused by a fungal pathogen that loves soggy, low-oxygen conditions. 

Potted tomatoes really dislike “wet feet.” If you imagine standing in a puddle all summer long, this is what an overwatered container plant feels like. The plant roots cannot properly breathe or function in waterlogged conditions.

How to Prevent Overwatering

First, ensure your container has adequate drainage. A large drainage hole at the bottom is ideal. Porous materials like terracotta and fabric pots are also useful for wicking away moisture. The tiny holes in the sides of those pots allow airflow to reach the root zone, which can prevent anaerobic conditions that lead to root rot. 

Next, prioritize checking your potted plants on a regular basis. A watering schedule (i.e. “water every other day”) is not ideal for container-grown tomatoes. Weather and conditions are always changing, so you cannot guarantee that the plant needs water every other day. Instead, use your finger to check the soil moisture. Make this a habit every time you walk by your plants. 

Lastly, check the drainage of your soil. Container plants tend to need even better drained soil than a raised bed or in-ground bed. This is because the soil is confined to a smaller space. Water should flow effortlessly through the soil profile. If you pour water onto the top of the soil, it should not puddle up. Puddling and slow drainage are signs that the plant needs to be repotted in a better mix.

Avoid adding clay-heavy garden soil into a container. If the plant is struggling with excess moisture, you can always repot it. Tomatoes are very amenable to transplanting as long as you are gentle and thorough. Use the transplanting process as an opportunity to check the roots for signs of rot. Prune away any brown, black, or mushy roots and sanitize your tools regularly.

Best Container Irrigation System

An olla (pronounced “oya”) is the best way to irrigate potted tomatoes. This ancient clay pot irrigation system is ideal for gardeners who tend to overwater. An olla is a porous terracotta pot that is buried in the potting soil near the plant’s roots. The olla is filled with water from the top and naturally releases moisture into the soil as needed. 

Thanks to an intriguing scientific phenomenon called soil moisture tension, the tomato roots only pull the amount of moisture they need. Once the soil is saturated, the olla stops releasing water through its porous earthen walls. All you need to do is bury the olla at the right depth and regularly check that it is full.

Too Little Water

A lack of water can be just as problematic as too much water. If the soil is pulling away from the edge of your pot, it is likely too dry. Tomatoes are very thirsty crops, and container-grown plants are particularly vulnerable to drought stress. You may need to water your potted plant every day, every other day, or every three days, depending on the container size and the weather. 

The root zone of a container plant is limited by the volume of soil. There is no way for the roots to reach deeper in the ground, therefore you must ensure they have everything they need in a smaller space. Larger pots can go longer time frames without water. However, plants that are loaded with fruit naturally need more water to keep producing tomatoes.

A lack of water is detrimental to tomato harvests and can dramatically reduce the yield, flavor, and texture of your fruits. After all, a tomato is about 95% water. Large-fruited varieties like beefsteaks are particularly in need of consistent moisture. 

But there is still something even worse than drought stress: huge fluctuations from dry to wet. If you go from drastic underwatering to dramatic overwatering, your tomatoes will be very unhealthy. The fluctuation from bone-dry to soggy soil is a major cause of blossom end rot, fruit cracking, and disease issues.

Shallow vs. Deep Watering

Overly frequent shallow watering is the main mistake that leads to drought stress. Frequent, shallow irrigation means giving the plant small amounts of water almost every day. This is not beneficial for root health or fruit production.  

Shallow watering only penetrates the upper few inches of soil. The bottom part of the container (where most of the roots are) remains dry and dehydrated. This inconsistent moisture can lead to major issues like low fruit production and blossom end rot.

In contrast, deep watering is ideal for tomatoes. This practice helps maintain consistent moisture so that there is always water available in the lower parts of the pot, even if the upper inches of soil dry out on a hot day. Remember, deeper soil is insulated against weather extremes because of its thermal mass and protection from the sun. The lower parts of the container act like a backup reservoir of water.

Whether growing in containers or beds, these plants prefer larger drinks of water at once. This means that you should irrigate less frequently but run the irrigation until water pours out of the bottom drainage hole. If there is no drainage hole in your pot, you may have to reach your arm in at the edge of the container to feel if the soil is moist at the bottom of the pot. 

Here is a quick reference chart to help you further understand the difference between these types of irrigation: 

If you still feel confused about irrigating your potted tomatoes, try an olla. This clay pot irrigation (described in the previous section) is perfect for creating a balance between underwatering and overwatering.

Preventing Blossom End Rot

Have you noticed rotten, ugly “butts” on the bottoms of your tomatoes? Blossom end rot is commonly mistaken as a disease, but it is actually a physiological issue. It causes the flower-end of tomato fruits to turn brown, black, or mushy. The main cause of blossom end rot is a calcium deficiency. However, this doesn’t mean you have to dump on the eggshells, oyster shells, or other calcium fertilizers. 

Most garden soils (including potted soil blends) actually have plenty of calcium. The real problem is calcium availability. Improper watering is a top reason why your tomatoes are not able to uptake the calcium in the soil. The fluctuation from dry to wet is stressful for the plant, causing it to become mineral-deficient. Ironically, a similar response happens to humans when they become stressed. Stress is detrimental to our health, and it significantly harms your tomatoes, often causing them to rot while still on the vine!

Moral of the story? Keep the soil consistently moist. Try to avoid long periods of dryness, and water deeply but less frequently to keep those lower roots happy.

Containers Without Drainage Holes

It’s more difficult to water if your container doesn’t have adequate drainage. In regular garden beds, water can always flow deeper into the ground. But in a container, water must have some way to exit the bottom of the pot. It is a major mistake to plant tomatoes in pots without drainage holes. This can cause issues with root rot, overwatering, and stunted growth. 

Before you plant your tomato, check that there is at least one large hole at the bottom of the pot. So-called “self-watering” planters are not always the best because you cannot see the water pour out from the bottom. A standard pot-and-saucer makes it easier to irrigate. When the saucer fills with water, you know that you’ve properly irrigated the entire soil profile.

Grow bags are an exception to this rule. These fabric pots don’t have visible drainage holes, but they are made of permeable, breathable fabric. The fabric will naturally wick away water and help the roots breathe.

Growing in Low Light Areas

Container-grown tomatoes still need just as much light as their garden counterparts. Full sunlight is crucial for success! These plants are native to South America, where they’ve evolved for centuries under the hot, bright sun. A minimum of six to eight hours of direct sunlight per day is necessary for proper flower and fruit production. 

The best thing about container growing is that your plants are mobile! A lack of sunlight is easily remedied by moving your tomato to a brighter location. Ensure the area is south-facing without any major shadows from buildings, shrubs, trees, or fences. 

If your tomato was growing in a very low-light area, make the adjustment easier by gradually introducing more light. Move it closer to the brighter sun every few days. Do not suddenly move a shaded plant into full sunlight, as this can cause leaf scorch and intense stress. The plant needs time to adapt.

Wrong Variety Selection

Some tomatoes are just too big for containers. Unless you have a giant grow bag or raised bed, it is best to stick with compact varieties. In general, determinate (bush) tomatoes are the best for containers. These cultivars are bred to remain small and shrubby while still producing a lot of fruit at once. Of course, you can still grow indeterminate (pole) varieties as long as you provide a larger pot, trellis, and regular pruning.

When searching for tomato seeds or seedlings, look for plants labeled as “compact” or “suitable for pots.” These plants naturally grow better in containers because they don’t require as much space. They often have shorter nodes between leaf sets and are bred to produce dense yields on smaller vines.

Lack of Trellis or Support

Growing a potted tomato without a support can be a recipe for disaster. A wind storm can easily knock over your plants, especially if they are growing in smaller pots. Moreover, many varieties cannot support themselves once they are loaded with fruit. A simple tomato cage, T-post, or trellis system makes a huge difference in yields and maintenance. Lack of support is a common reason for messy container gardens and diseased plants.

Determinate tomatoes naturally have stouter, bushier growth. Still, most require a tomato cage to keep them contained. Indeterminate tomatoes have long, rambling vines that will quickly spill over a pot. You do not want fruits to develop on the soil, as this can predispose them to rot and pest damage. Instead, use a T-post, stake, or a taller tomato cage to train them upward.

Trellising is a great way to improve yields in a small-space container garden. By training the plants upward, you maximize vertical space without taking up extra ground area. More importantly, you can prune away side shoots (suckers) to help the plant focus on fruit production. Choose just one or two main stems where the plant can grow its fruit, then prune away the lateral shoots. This will create a tidy potted plant that is loaded with tomatoes. Removing excess suckers also ensures proper airflow to prevent disease.

Lack of Pruning

Speaking of pruning, pro container gardeners should prioritize removing suckers from their tomatoes. After all, you want to make the most of a small space. If you neglect pruning, the tomatoes may overgrow a ton of foliage and fail to produce as much fruit as you desire. A lack of pruning can also lead to overcrowding.

Suckers are the side shoots that grow in the “elbow ditches” of tomatoes, right where a leaf stem intersects with the main stem. Indeterminate varieties produce more suckers than determinates. They are called suckers because they “suck” energy away from fruit production. Each sucker can grow an entirely new vine that is the same size as the plant. If you snip off the little suckers, it sends a message to the plant to focus on growing flowers and fruits.

Always use clean, sanitized shears. Remove prunings from the garden to prevent disease.

Overcrowded Plants

You should never overcrowd container-grown tomatoes! It is highly recommended to only grow one plant per pot. If you wish to grow multiple tomato plants in the same container, a small raised bed is a better option. This is because tomato plants need at least 24-36 inches of space in every direction in order to grow to their fullest potential. 

Overcrowded plants must compete for water, nutrients, and light. Too much competition is bad in any space, but especially in a small pot with limited resources. Nobody wants to be crammed like sardines in a subway, and your plants don’t want to be crammed into a small pot together. One well-cared-for plant in a large pot will typically out-yield a pot of two or three overcrowded plants. 

Lack of spacing also leads to a lack of airflow, which creates conditions for disease. Powdery mildew and blight spread rapidly between overcrowded tomatoes. If leaves are brushing up against each other in a jungle of growth, they are probably too close together. It helps to space your pots 8-12 inches apart to give each plant sufficient space to breathe.