No Tomatoes? What’s Nitrogen got to do with it?

Are your tomato plants amazingly tall and lush green but lacking in fruit production? Why does this happen and how can you fix it?

Two of our tomato plants are probably about 7 feet tall (7.13 meters) at this point, and perhaps even taller. They look healthy. The leaves and stems are brilliant green, but the plant is lacking in tomato production. I thought I’d be overrun with tomatoes this year, but I most certainly am not. Why do these two plants look so good but aren’t producing tomatoes?

There are two common reasons that tomato plants grow tall and yet don’t produce fruit:

they either aren’t getting enough sunlight or
there’s too much nitrogen in the soil

When plants don’t get enough direct sunlight, they’ll stretch and become spindly as they search for the sun. Tomato plants need 6-8 hours of sun a day. Since ours are certainly getting full sun, that leaves nitrogen as the problem.

Nitrogen can be thought of as the green element in growing plants. It’s what helps plants with photosynthesis and makes plants green. If your plant leaves start to turn yellow, that is an indication that it is lacking in nitrogen. Similarly, if your plant is receiving too much nitrogen, all its efforts are being put into growing tall and green and not being put towards fruit production.

How do you end up with too much nitrogen?

It’s important to check your soil pH before planting. This will indicate whether you need to amend your soil. Tomatoes like soil that is slightly acidic, which has a pH between 6 and 6.8. You can pick up an inexpensive soil test kit at a local garden center or nursery. Mine was only $7 USD. I tested the soil with our children, which was a fun learning opportunity. What kid doesn’t like digging in the dirt and shaking things up? That’s all there is to the test. You simply scoop up soil, mix it with distilled water and one capsil from the test kit then place it in a window for a minute. You then match the color of the liquid to the pictures on the side to see what your soil’s ph level is. It’s that simple and inexpensive.

What do you do when your ph level is not between 6 and 6.8?

Our soil was between a 5.5 and 6 depending on which part of the garden we tested. In our case, our soil was acidic and we needed to add lime to our garden beds. Lime is sold as pure calcium carbonate or ground dolomitic limestone. You can find it at a garden center or online. Simply follow the directions on the package to amend your soil before planting your tomatoes.

If your soil on the other hand is too high in alkaline, you’ll need to lower the ph level. You can add elemental sulfur, or a sulfur compound like aluminum sulfate to reach the ideal ph level for tomatoes. Again, this is available in garden centers and online. Follow the directions on the package.

I’d like to re-emphasise following directions. Apparently I didn’t do a good job of it on two of the tomato plants and that’s why they grew so tall and didn’t produce many tomatoes.

So what can you do to fix this problem if you don’t amend your soil before planting?

Don’t panic if it’s late in the season and you didn’t test or amend your soil before planting. While it’s ideal to start off with the right soil quality, you can still fix the problem mid season. Even if you did amend your soil at the beginning of spring, if you fertilized your tomato plants you might have added too much nitrogen if you didn’t use the correct fertilizer. Many new gardeners make the mistake of using 10-10-10 fertilizer throughout their garden but that puts too much nitrogen in the tomato bed. While tomatoes are heavy feeders and require nitrogen, phosphorus and potassium, they actually need less nitrogen and more phosphorus to produce flowers and then fruit. Look for a fertilizer made specifically for tomatoes or one that is low in nitrogen, high in phosphorus and has a medium to high amount of potassium. I suggest Jobe’s Organic Fertilizer.

If your tomato plants aren’t producing flowers by mid season and you’ve fertilized appropriately, prune leaves and pinch off suckers. This will prevent the plant from spending so much energy on stem and leaf growth and put more energy into producing flowers. Remember that tomatoes like it warm, but not hot. They will not produce flowers if the temperature is over 85°F(29°C). At this point in the season, depending on where you are, temperatures shouldn’t be quite as hot as the height of summer. As the temperature starts to drop, more flowers will blossom leading to more fruit.

Make sure to continue to water your tomato plants, giving them one to one and a half inches of water a week if it doesn’t rain. Don’t let the soil dry out. Keep it moist, but not sitting in a puddle.

If after fertilizing, watering and waiting and you still don’t see flowers when the temperature is ideal for blooms, try mulching with straw or mix sawdust into the top layer of the soil to reduce nitrogen further. You can also add bone meal to add phosphorus.

Growing tomatoes can be fun and exciting, but it has a learning curve. There’s a reason tomatoes are the number one vegetable (though technically a fruit) gardeners in North America choose to plant. Have patience and try a few things until you find what works for your garden.