Why Are My Tomato Plants Collapsing? (and how to prevent it from happening)

Tomatoes are one of my favorite plants to grow in the greenhouse. No matter what other plants I have growing, I always have space for 3 or 4 varieties of tomatoes.

Although tomatoes are considered a staple of the homestead, they can sometimes be a little finicky to grow. It is not uncommon to find your tomato plants are turning yellow, failing to flower, or sometimes barely growing at all.

In this article, I answer the frequently asked question ‘Why are my tomato plants collapsing’.

The three main causes of tomato plants collapsing are improper watering, lack of proper support, and Fusarium Fungus. Tomato plants may also collapse due to a lack of nutrients, insufficient light, poor soil drainage, and exposure to cold weather.

Why Are My Tomato Plants collapsing?

There is nothing more frustrating than finding the tomato plants you have invested time and effort into are suddenly starting to collapse.

Sometimes tomato seedlings suddenly collapse and wither away, other times it happens to young plants just as they start to produce fruit. It can even happen to mature plants that are bulging with tomatoes.

The cause typically varies depending on the age and size of the tomato plants when they start to collapse. Below I have listed the most likely reason depending on the size of the tomato plant.

  • Seedlings – Seedlings typically collapse due to damping-off caused by a soil-borne fungus.
  • Juvenile plants – Improper watering or transplant shock can cause juvenile tomato plants to collapse.
  • Mature plants – Lack of proper support or irregular watering are the most frequent causes of mature tomato plants collapsing.

Tomato Seedlings Collapsing

When tomato seedlings collapse, the reason is typically damping-off. Damping-off is a general term used to describe tomato seedlings that suddenly die as a result of a number of different soil-bourn fungi.

Otherwise healthy tomato seedlings can go from strong little plants to mush in as little as 48 hours when affected by damping off.

Damping-off most frequently occurs in damp and cold conditions.

There are currently no known treatments or cures for damping-off and it is generally accepted that good hygiene practices along with only using fresh potting compost are the best ways to prevent damping-off.

In my experience, the best ways to prevent damping-off killing your tomato seedlings are;

  • Only use good quality, fresh potting compost (never be tempted to reuse old compost)
  • Thoroughly clean pots and seed trays between uses
  • Always water seedlings from below rather than overhead
  • Remove and dispose of any tomato seedlings that show signs of damping-off

Juvenile Tomato Plants Collapsing

Sometimes, tomato plants will successfully survive the germination process and grow large enough to be considered juvenile plants, only to start to collapse and eventually die off.

Collapsing at such an early stage in a tomato plant’s life can usually be attributed to one of three different reasons.

Delayed transplanting

It can be tricky to get the timing right and to know when to transplant your young tomato plants from their seed tray to individual pots.

In my experience, the best time to transplant your tomato seedling is once they reach around 3″ to 4″ (7.5cm to 10cm) tall. Leave them much longer and they often become leggy and start to crowd each other out.

If tomato seedlings are left in their seed trays too long, the chances are they will use up all of the nutrients in the potting compost. Potting compost is only designed to provide enough nutrients for the first 5 or 6 weeks of a seedling’s life.

Tomato seedlings that are left in their seed trays too long often end up leggy with poor general growth and may eventually end up collapsing under their own weight as they have not developed properly.

Seedlings that get too large in their seed tray will also compete with one another for available light, meaning many of the seedlings die due to lack of sunlight.

Underwatering or Overwatering

Both underwatering and overwatering juvenile tomato plants can cause the plants to collapse.

With underwatering, the plant will quickly dry out, leading to the plant stem crumbling and collapsing under the weight of the plant.

When a young tomato plant is underwatered, the walls of the cells that make up the individual parts of the tomato plant begin to break down which leads to the plant collapsing.

If young tomato plants are overwatered, it can lead to the roots or the bottom of the stem rotting or becoming susceptible to fungus, both of which will cause the tomato plant to collapse under its own weight.

Even if the plant does not collapse, young tomato plants sitting in soil that is constantly wet may die due to the roots not being able to absorb oxygen or nutrients from the soil.

Fungus and disease

Although tomato plants become less susceptible to soil bourn fungus the larger they grow, they do not become totally immune, and diseases such as Fusarium and Verticillium Wilt can still affect young tomato plants.

As with seedlings, if these diseases are present in the soil, there is a good chance they will attack the tomato plants, causing the plants to collapse and die.

Much like with a seedling in a seed tray, young tomato plants kept in cool, damp conditions are more likely to succumb to one of these diseases.

To prevent both Fusarium and Verticillium Wilt diseases from becoming established, use good hygiene practices when working in and around your tomato plants, and never reuse potting soil, especially if there is a chance you suspect the diseases may be present.

Transplant shock

Transplant shock is often poorly understood and can be hard to mitigate.

Transplant shock is essentially when a young tomato plant is removed from its existing seed tray or pot, and planted in another location.

The main causes of transplant shock in young tomato plants are;

  • Root damage – removing the tomato plants from their existing location too aggressively can lead to roots being damaged meaning the plant is unable to take up sufficient water or nutrients once in its new location.
  • Lack of watering prior to moving – whenever plants are transported from one pot or tray to another, they should be thoroughly watered, ideally for a few days, prior to being moved.
  • Failing to harden plants if moving to an exposed location – when tomato seedlings are grown in the warm, protected environment that a greenhouse provides them, they often need to be ‘hardened off’ prior to being moved to an outside location. Hardening off means exposing them to cooler conditions for a few hours each day in a week or two prior to moving them to the new, colder location.

Mature Tomato Plants

Even mature tomato plants are not immune to collapsing without warning, breaking, or killing the tomato plant altogether.

In my experience, the most frequent cause of a mature tomato plant collapsing is a lack of proper support.

A mature tomato plant, fully laden with ripening tomato is a surprisingly heavy plant. If you have ever tried picking one up, you will know what I mean.

Many tomato growers use thin, flimsy pieces of bamboo cane to support their tomato plants. While these work well for smaller tomato plants, the canes are often insufficient for full-grown, mature plants.

Unfortunately, once your tomato plant is full-grown, it can be tricky to swap the small cane it is already growing up.

I have found that using stout, 1″ x 1″ (25mm x 25mm) lengths of timber as supports will help keep your tomato plants upright no matter how laden with fruits they become.

It is also important to remember to regularly tie your tomato plants to whatever they are being supported by.

We have probably all been guilty at one time or another of tying our plants to the support when they are 6″ (15cm) tall, then never doing it again, meaning the tomato plant eventually flops over under its own weight.

Other reasons tomato plants collapse

There are many other reasons tomato plants may collapse. Below I have listed some of the ones that, in my experience at least, may affect your tomato plants.

Lack of nutrients

A lack of available nutrients in the soil can cause tomato plants to collapse at any point in their lives. Plants are actually fairly complex things that require a broad range of nutrients. Some in large quantities, others in microscopic quantities.

The majority of the time, these nutrients will be present in the soil and we don’t need to worry about them. However, if we grow our tomato plants in the same spot year after year without feeding the soil or replacing it with fresh soil, there is a good chance we can starve the soil of nutrients, meaning they are not available for the tomato plants.

If like me you grow your tomato plants directly in the ground, you will need to add fresh compost or well-rotted manure to the ground each year to add nutrients back into the soil.

If you grow your tomato plants in pots, you should always use fresh potting compost to ensure there are sufficient nutrients available to the plants.

Reusing potting compost will lead to weak plants that may collapse or fail to produce a good quantity of fruits.

Lack of light

Although a lack of light is likely to leave your tomato plant leggy and looking yellow, with fruit that fails to ripen properly, a lack of light can also lead to a tomato plant collapsing.

Tomato plants need light to photosynthesize (produce energy from the sun’s rays). Without sufficient light, the tomato plants will struggle to produce strong stems, which can in turn lead to the tomato plant collapsing under its own weight.

The advice I always give is to plant your tomato plants in the sunniest spot you have. Not only will this ensure your tomato plants grow strong and tall, but also your fruits will ripen and be sweet.

Poor drainage

As discussed above, tomato plants need water, but when it is in excess, or it does not drain away properly, it can lead to the roots of the plant sitting in water or waterlogged soil.

Roots need to take in oxygen through their roots as well as water and if the roots are waterlogged they will not be able to take any oxygen in.

Excess fruit and leaves

It can be tempting to allow your tomato plant to grow as many tomatoes as possible, but in reality, there is only so much fruit one plant can support.

To get the best crop from our tomatoes, and reduce the chances of the plants collapsing under their own weight, we homesteaders have to be disciplined and remove excess fruits and for that matter, excess leaves that are growing.

In Conclusion

Tomatoes are the staple of the homestead, and they are an amazing crop that can be grown to be eaten fresh or preserved for use later in the year.

It can be incredibly frustrating when your tomato plants suddenly collapse and die.

If your plants are suffering, work through the list above, and hopefully, you will be able to find the reason and fix the problem.

If you found this article helpful, why not check out another one I wrote recently titled ‘Why are my homegrown tomatoes mushy?’

Arya Patel

Arya Patel is HomesteadSavvy.com’s fruit and vegetable editor. Arya has been homesteading for well over a decade and over that time she has grown countless varieties of fruits and vegetables. She aims to become completely self-sufficient over the next 5 years.
Fruit & Vegetable Editor

Article Sources:

  1. Tomatoes rhs.org.uk
  2. How to grow tomatoes Gardenersworld.com
  3. Tomato Wikipedia