So, your healthy, bright green tomato plant is suddenly turning yellow; seems like a major cause for concern, doesn’t it?
We’ve all been there, worried that our tomato plants were doomed from that point on!
However, yellow leaves can mean a variety of different problems for tomato plants- they can be incredibly easy fixes, or they may be indicative of a bigger problem.
Before you remove any leaves from your tomato plants, be sure that you’re doing something that benefits the plant as a whole; if you take yellowing leaves from a determinate plant, you may actually hurt the plant more than you’re helping it.
Some cases of chlorosis (yellowing leaves) can be fixed or reversed, while others can’t. We’re going to cover the major causes, and what you should do.
Nitrogen Deficiencies: Reversible Chlorosis
If your tomato plants are getting quite pale and looking more on the yellow side of things rather than green, you may be dealing with a nitrogen deficiency.
For nitrogen deficient plants, you should not remove the yellowing leaves. Instead, give the plant a good feeding (foliar, if possible) and keep an eye on the plant. Eventually, the plant will “green up” as it begins to absorb the nitrogen.
On the flip side, you should not overfeed tomato plants with nitrogen; if you do so, you’ll wind up with gorgeous plants that produce more foliage than fruit, that may also be quite weak structurally due to rapid growth.
Fungal Infections & Control
If the chlorosis on your tomato plant’s leaves is due to a fungal infection, you should remove all affected leaves. In most cases, fungal infections do not completely kill plants. Instead, they tend to be more of a mild inconvenience. As the growing season progresses, you’re going to deal with a fungal infection much more often than you might think.
If you’re dealing with fungal-related chlorosis, take a look at other symptoms that may have caused the yellowing:
Are the tips of the leaves turning brown?
Do you see brown or black spots appearing, that are surrounded by yellow discoloration of the leaf?
Are ulcers appearing on fruits, that are unrelated to blossom end rot?
Do the stems or branches have growths that seem to look like mold?
If fungal infections are the culprit, be sure to clean your cutters or pruners to remove infectious tissue, as you don’t want to spread disease among your plants.
Dying Leaves / Lack of Sunlight: Is It Time to Prune?
As the tomato vine grows, you’ll notice that the oldest leaves and branches will die off, leaving the bottom of the vine relatively bare.
This is a natural process, especially among the indeterminate vining varieties. As the lower leaves are shaded, they have less and less access to sunlight.
If the leaves are beginning to die, I highly recommend pruning them to improve airflow, reduce the risk of fungal infections, and to allow the plants to redirect resources from those dying leaves to younger, newer leaves.
You do not have to cut these leaves off, but I recommend doing so if they are wilting, shriveling up, or turning brown. In this state, they pose no benefit to the mother plant.
Magnesium deficiencies are fairly easy to address, and you can do so with epsom salts!
Overwatering Tomato Plants
If your tomato plants are sitting in soil that is far too wet, you may notice a compounding issue; not only with the leaves turn yellow due to excessive amounts of water, but you’ll likely also see fungal infections running rampant.
This can be a common tomato problem in clay soils, where planting holes may act like bowls, filling with water than takes quite some time to drain.
If this is the case, immediately cease watering and allow the plant’s roots to dry out some. As the plant encounters more ideal moisture levels, the yellowing will stop and fungal infection will begin to taper off; be sure to remove any infected leaves though, and be sure that there is plenty of air flow between plants.