Tomatoes are some of the most beloved fruits for novice and experienced growers alike. Their vibrant red hues signify success and yummy tomato slices and sauces to come. Tomatoes are especially easy to grow in small “urban farm” settings such as a small deck or teeny backyard. Your tomato plants’ yellow leaves could be a wake up call for you to address some of the soil or bacteria issues it may face. Keep in mind that a few yellow leaves at the base of your plant is quite normal. Not all the leaves on a growing tomato are going to get adequate sunlight or nutrients from the soil. When more than a third of your leaves appear to be yellowing, you should take action.
Unfortunately, the causes are hard to pinpoint. Below is a list of what the yellow leaves may mean. Ultimately you the best person to judge what could be going on.
Soil pH problem. Your soil has the necessary ingredients it just needs to be correctly balanced. Really? And yea, it could be complicated if you get into the details- but keep it simple as possible. Tomatoes like soils with a slightly acidic pH or from 6.0 to 6.8. (Remember a pH of 7 is neutral)
Lack of Nitrogen in the Soil. Ok, so this basically a soil pH problem. More specifically a common cause for those yellow leaves to pop up. You could go the nerdy and thorough route by purchasing a basic soil kit and analyzing what you got (hint: you should probably invest in a home soil kit anyway). Or if your local or purchased soil is notorious for being low on nitrogen then could do well by adding some nitrogen fixers into your soil mix. Solution: add your compost. If you are weak on composting then you can buy the stuff or borrow from a neighbor.
Lack of Iron. This is another common soil composition problem. If your tomatoes’ soil lacks iron then their leaves will show it by turning yellow. You can get iron into the mix by adding compost. (See the compost trend here?)
Too much or Too Little Water. Do you over-love your plants that you give them too much water? Stop, or at least hold back for a few days and see if they start to turn green again. If you are a skimpy water-giver or your soils don’t hold moisture very well then try up-ing their daily dose. How can you tell? Feel the soil before deciding whether too much or too little water is the problem.
Aphids. These little green guys are tomato monsters. If you spot them go buy some lovely Ladybugs that will eat them all away. How much does everyone adore Ladybugs? See bigger buggers than aphids? They’re probably the Tomato Hornworm. Just pick them off and flick them away.
Lastly, here’s a permaculture plug that may get you thinking about a holistic garden design.
Permaculture Style Solution: Set up a guild system to avoid this problem- plant tomatoes with nitrogen fixing plants (peas, beans, clover). Set up compost system on site. Be sure to provide quality mulch at least once a year.