Tomato Seedlings Not Growing? Here’s Why

Tomatoes are super fun to grow and generally a rather good starter plant for those new to gardening. Getting them into the dirt and sprouted is the easy part, though – if your tomato seedlings are not growing, there are a few key things to look for. Tomatoes generally really like consistent amounts of water, temperate climates, and good attention – so what might have made them stop growing?

The most common reasons that tomato seedlings are not growing are poor temperatures or weather, over or under watering, and a lack of nutrients.

Keep reading for all of the advice, tips, and tricks that you could possibly need to get your tiny seedlings turned into tasty giants in no time.

4 Reasons your Tomato Seedlings Are Not Growing

We’ll start with the simple stuff and move onto nutrients and proper plant care in a moment. As a primer, it’s good to know that you’ll generally want to plant tomatoes in mid-late spring and plan on them taking at least eight full weeks of proper care to grow. This means that if you’ve missed a day or two of care, or if things have gotten gnarly in your neck of the woods, you may have a dead plant on your hands. Without further ado, let’s get into it, shall we?

Temperatures

As with all living things, tomatoes have an ideal temperature range that they prefer. If things get far above or below that range, you will likely have dead or dying plants on your hands. So what’s the ideal temperature range for tomatoes to grow in?

The perfect temperature range for tomatoes to grow and fruit is between 20 ºC and 24ºC, though this varies by type of tomato plant. Anything below 14 ºC can prevent growth and fruiting, and anything above 32 ºC can damage the fruit.

If things get too hot or cold in your neighbourhood, it may be time to move your tomato plants (if they’re potted). If you don’t, you run the risk of them dying or not fruiting.

Specifically, temperatures below 12 ºC are very dangerous for plants (so don’t plant them in winter). Additionally, temperatures above 38 ºC (especially over more than a single day) can kill the plant.

Watering

All plants need some amount of water to survive. Generally, as a rule of (green) thumb, tomatoes prefer to be regularly watered over excessive watering.

This means that watering in the early stages of the plant’s life should occur daily in the morning. This will prevent the soil from getting boggy and literally drowning the root system of your tomato plant.

Later on in the life cycle of your tomatoes, you’ll need to water them more, especially if they’re in containers or pots.

You generally need to provide 2.5-4 cm of water per week for tomato plants in dirt. Those in pots will need roughly 4-6 cm of water per week.

This is because pots store heat more effectively and faster than dirt alone will. If you don’t want the tomatoes baked quite yet, consider watering them twice a day. A final good tip is to feel the dirt with your finger before watering. If it comes out moist, you can water less than you would normally. If it’s dry as a bone – drench that baby.

Feed Your Plants

If your tomato seedlings are not growing, it may be a sign of nutrient deficiency. While fertilisation is rather commonly known as a good practice for gardening, it’s good to mention again.

Use fertiliser and additional nutrient supplements for your plants – especially if they’ve changed colours recently.

We’ll get to the colour change in a second, but let’s start with what nutrients your plants need and how to provide them. Tomatoes generally run low on potassium, nitrogen, and phosphorous – especially in poor soil.

If your soil has a phosphorous deficiency, your plant will grow more slowly and take root less efficiently. If there’s not enough nitrogen, the yield of the plant will be lessened. And if you’re short on potassium, you’ll be able to see it. The fruit will be blotchy, remain green or yellow (rather than red), and will be rather bland and hard when eaten.

To fix a deficiency of any of the above, purchase fertiliser in combination with phosphorous, potassium, nitrogen, and/or bonemeal horticultural supplements. These will help your soil be a better home for the tomatoes and result in a tastier final product.

Yellow Seedlings

If your seedlings are yellowed, this is a sign of something called chlorosis. In short, this means that your plant is yellow when it shouldn’t be. It’s a sign of the plant lacking chlorophyll – the pigment that allows plants to take in water and sunlight.

Generally, chlorosis is caused by poor soil drainage, damaged roots or compacted roots, pests, poor soil pH, or nutrient deficiencies.

To fix this, begin by examining your soil mix and adding the things mentioned above, ensuring it can drain well. Boggy soil will encourage bacterial growth, root rot, and much more – it’s generally bad for most plants.

You can try to repot or replant the tomato plant and see if that helps, otherwise, you’ll need to look at soil pH and insecticides. You can find guides to those here (pH testing for grass seed) and here (helping runner beans germinate), respectively.

Final Thoughts

Tomatoes require a good bit of care and attention. While they’re not overly needy, it’s vital that you’re aware of outside temperatures and how much you’re watering them. Ensuring things don’t get too hot or cold (and moving the plants when it inevitably does) will keep them happy and healthy.

Additionally, making sure to water daily (or more, as needed), along with monitoring your plant’s soil will improve their performance and lifespan drastically. And finally, don’t be afraid to mess with your soil – that’s half the fun of gardening anyway! You get to play in the dirt and it’s actually a hobby! So ensure your soil can drain properly and pay attention to your plant. If it’s drooping or changing colours, it’s time for you to listen to what it’s telling you.

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About the Author Harry Thompson

Involved in home renovations throughout his life, Harry is an expert in everything to do with home and garden DIY. In his spare time, he enjoys cooking and tending to his garden.