As an Amazon Associate, GrowJourney earns from qualifying purchases. Read more: terms of service.
Trying to figure out the right way to grow potted tomatoes without killing them? We’ll show you the five most common ways people kill their potted tomato plants, and how you can avoid making the same mistakes in order to enjoy piles of fresh tomatoes this summer.
Last updated: May 7, 2019
We’re not judging you. After all, you didn’t intend to murder your potted tomato plants. It just seemed to happen.
In the spring, you started with the noblest of intentions. You filled your pots with soil, plopped in some tomato plants or seeds, then waited.
Things started off well… Your tomato plants looked happy and started growing. Then along came summer and soon your tomato plants were limp, brown, and crispy. Those bountiful summer-long harvests you’d hoped for didn’t quite materialize.
“Next time will be different,” you tell yourself.
Well, we’re here to help make sure that your next time (right now) is different! Below are the top-5 reasons that potted tomato plants die, and how you can avoid these problems with your potted tomato plants this summer.
Top 5 Reasons You Kill Your Potted Tomato Plants… And How To Get It Right Next Time
1. Wrong Sized Pots for Tomato-Sized Plants
As kids grow, they need bigger clothes. Planting a large indeterminate tomato in a 1 gallon pot will eventually work out like trying to put your college kid into toddler clothing.
The roots will end up strangling each other, the plant won’t be able to get enough water or nutrition, and eventually it will die.
Get the right size containers for your tomatoes (see below). As we’ve written about here, pot sizes are not standardized and are notoriously difficult to decipher.
However, here are some general recommended minimum pot size numbers for you to work with depending on the type of tomato you’re growing:
- Micro-dwarf tomato varieties – minimum 3 gallon pots/grow bags
- Dwarf tomato varieties – minimum 4 gallon pots/grow bags
- Large/indeterminate tomato varieties – minimum 6-8 gallon pots/grow bags
Keep in mind that these are *minimum* sizes, which means these are the smallest sizes at which you can expect your tomato plants to be able to grow well. Larger sized containers would be ideal.
*Each sized pot and growbag listed above is available in the GrowJourney organic supply store, which is conveniently sectioned off by container size (in gallons).
2. Water Stress
In the intense heat of summer, tomato plants need lots of water – and they need consistent water. Planted in the ground, their large root systems and mychorrhizal fungi partners can source water from a large growing radius.
However, when grown in pots/containers, tomato plants can only access whatever water is immediately in the pot. Making matters worse, the water in the potting soil is warmed faster (heated from all sides) and evaporates faster than it does when it’s in good in-ground garden soil.
Tomato plants growing in a pot of dried out soil get stressed. Severely stressed plants are more prone to disease and are unable to set fruit or carry their fruit to maturity. Depending on how dry they get, your potted tomato plants may even die.
A. If growing tomato plants in conventional pots & grow bags…
Place saucers under your pots/grow bags to trap the water that flows through the pot when it rains or gets irrigated.
Also, when you’re watering your pots, fill the saucers up in the morning (if the saucers are empty) so that the water is soaked upwards through capillary action, helping ensure better moisture distribution.
B. If growing tomato plants in sub-irrigated planters…
If you haven’t already invested in pots, we highly recommend getting sub-irrigated planters (SIPs) instead. Read all about SIPs here, including how to make your own.
SIPs are much more water-efficient than traditional pots. Depending on the SIP you get, you may only need to fill the water basin 1-2 times per week in the summer, rather than watering every day like you need to with traditional pots and grow bags.
Another problem many gardeners run into when trying to grow potted tomatoes is “blossom end rot,” a dark rotten spot on the bottom of a tomato. Common causes of blossom end rot is inadequate water, calcium deficiency, and too much nitrogen fertilizer. Pot saucers and SIPs can help prevent blossom end rot as well.
*Saucers for every pot size plus our top-recommended sub-irrigated planters are available here in our store.
3. Wrong Type of Soil
Soil is soil, right? Nope.
As we’ve written about here, seed starting mix, potting soil, and garden soil are each quite different. If you dig soil out of your garden and plop it in to your pots, it will soon form an impenetrable brick, choking your tomato plants’ roots in the process.
Make sure you use a good OMRI listed/organic POTTING soil (like this one) in your pots. Do NOT use garden soil.
4. Inadequate Nutrition
If you notice your tomato leaves looking yellow or your plants not growing, that’s more than likely due to inadequate nutrition.
For in-ground garden plants, we highly recommend focusing on biological soil fertility, e.g. developing the microbiology of your soil with composts and mulches to the point that your plants don’t need any chemical or mineral fertilizers.
However, inside a pot, nutrition is limited by space and the microbes are accordingly limited in how much nutrition they can cycle or source for your plants.
Even though your potting mix starts off with some fertilizer already in it, you’ll still need to plan to fertilize your potted tomato plants multiple times over the summer growing season.
Two good OMRI listed organic fertilizer options for potted tomato plants:
- liquid kelp emulsion,
- dry/granulated pellet fertilizer formulated specifically for tomatoes and similar veggies.
5. Airborne Diseases
Sometimes you do everything right, but an airborne foliar/leaf disease (fungal or bacterial) comes along and slowly infects your previously glorious potted tomato plants.
The leaves start turning brown or getting spots all over them. Then it spreads, either killing the plant or taking enough leaves to drastically reduce fruit production.
In an organic garden or farm, you fight biology with biology and you try to design your system so as to prevent problems from happening in the first place.
We love making actively aerated worm casting “tea” to use as a soil and leaf drench on our plants. However, that might be a little more work than most gardeners want to go through.
Thankfully, there’s a fantastic organic solution that also comes in an easy-to-use spray bottle: Serenade. Serenade is a strain of beneficial bacteria (Bacillus subtilis) that either consumes or outcompetes a huge number of pathogenic bacterial and fungal species. And, yes, it’s completely safe to humans, pets, and pollinators. You can eat your produce the same day as you apply Serenade.
For best results, we recommend using Serenade preemptively before you start noticing leaf diseases on your plants. However, it also works as a treatment. Spray on early in the morning or late in the evening once per week on a dry (non-raining) day to allow the beneficial bacteria adequate time to set on your leaves. If rain is frequent, use it more often.
- If you have a spray bottle and lots of plants, get the Serenade concentrate and make it as often as needed.
- If you don’t have a spray bottle or a lot of plants, a single ready-to-use bottle of Serenade will get you through the summer.
Another tip to prevent tomato diseases in your potted plants: don’t grow tomatoes in the same potting soil year after year, especially if your tomato plants had diseases last year. Use different types of plants or start with new potting soil this year.
Additional Tomato Growing (and Using) Resources:
- How to graft heirloom tomatoes on to disease-resistant rootstock
- How to make your own large, indestructible tomato cages that will last for decades
- GrowJourney’s complete guide to growing tomatoes
- 18 simple recipes to help you use up lots of tomatoes
We hope this information was helpful! Have questions? Ask away in the comments section below.
The featured image for this article is a tomato harvest from Monika Melsha, who grows amazing potted tomatoes each summer in Plymouth, MN.