Updated: May 19, 2020
Here I'm just going to copy and paste a couple of different articles I have found helpful. I can't stand all of the ads that other sites have, it's so distracting. This is just information about tomatoes, not trying to sell anything but knowledge.
But first let me tell you about my garden. My first garden was a disaster. I admit that, I admitted that while it was growing. No one will ever do something perfectly the first time, it takes time to see what can go wrong and to learn from your mistakes. I've had my garden now for 10 years and I still am learning things. Don't become frustrated, know that if you keep at it, you will get better. That kind of applies to all things in life, so just take a breath and relax. Gardening is supposed to be fun, if you aren't having fun, just don't garden. It's not for everyone, that's why we have farmers. So if gardens just cause you stress, my suggestion is to just head out to the grocery store. Life is too short to do things that cause you more stress.
My first garden was an interesting one. When my husband and I bought our house I was very excited because there was a small raised bed in our backyard. It was small, 5'X3', but it was mine. I was going to make it the most fabulous 5'X3' garden ever. I planted 3 heirloom tomato plants, a 6pk of carrots, corn, cabbage, broccoli, lettuce, kale, zucchini, and strawberries. I was so excited I called my neighbor over, an avid gardener of 50+ years, so that she could see what I had done.
Leslie came over and looked at what I had planted, she smiled and said, "You certainly have a lot of variety in there." And then laughed. I told her that I couldn't wait to watch everything grow. She laughed and said, "It will grow alright." And it did. It grew, and grew, and grew, and I came to realize how large some plants get. I had planted over 20 plants in a space that would comfortably fit 1, maybe 2, zucchini plants. Leslie watched my garden grow just as I did, she called over one day and asked, "So how is your garden doing?" I laughed and told her that perhaps I didn't realize how large mature plants were. She told me that she was going to mention something before, but that seeing for myself was the best way to learn. And learn I did.
The following year I knocked down that bed and built 2 other beds, 4'X8'. The year after that another 3 beds followed. Year after year, more and more beds and barrels were taking over my backyard. Digging out more lawn for plantable space, blueberries and strawberries replaced grass. I planted butterfly and bee attracting flowers to lure pollinators into my garden to help produce more and more fruit. It's really an addiction for me. I love seeing the transformation and evolution my garden goes through. Here is a picture before and after picture of my yard. I had a vision and it's slowly coming to fruition.
The second year I had a garden I had my tomatoes spaced properly, but I noticed that the leaves were turning yellow. I called over Leslie to see if she could help. She asked if I had been watering them. I told her that I watered every day for at least 15 minutes. She told me that was most likely the problem and to stop watering immediately. She explained that I was basically watering down all of the nutrients from the soil and that they were just being washed away. Tomatoes like to be watered, but they don't like to be overwatered. They like to be fertilized, but not over fertilized. They don't like having damp leaves, but they do like them to get watered occasionally. Basically they are like Goldilocks. Give them what they like though and they will produce amazing fruit that far surpasses anything you could find in a grocery store.
Another problem that I have found we have in the the PNW is flea beetles. UGH! They are little beetles that look like, you guessed it, fleas. They are tiny and black and hop from plant to plant. They will destroy your plant if you don't get to them soon enough. My suggestion is to look out for them because if you catch them early on they won't reproduce and completely ruin everything you have. If you see these tiny black things hopping from leaf to leaf, just smash them with your fingers, or place bowls that have a little dish soap in them with water. They love bright yellow and orange things, so if you have colored bowls, even better. I normally let most creatures live, only two things die under my hards, ants in my house and flea beetles in the garden.
So enough about my garden, here's some more information about tomatoes that I have found on the internet. If you want to read more about flea beetles, click here.
Yellow Leaves on a Tomato Plant?
Tomatoes are one of the few garden vegetables that can land their caretakers in a world of despair when problems erupt -- for all their trouble, it's a wonder anyone grows them. When tomatoes develop yellow leaves, it's unlikely to be caused by too much fertilizer, but could be due to other environmental problems or diseases. Fertilizing Tomatoes A home soil test kit will give you valuable information about your tomato patch. Tomatoes thrive with medium fertility and show problems when fertility is too high or too low. Usually, they don't require any feeding at planting time, unlike many vegetables. Successful tomato producers may wait to feed tomato plants until fruits are about the size of table tennis balls. At this point, side-dress tomatoes with a small amount of nitrogen fertilizer every four to six weeks until the final harvest. Signs of Too Much Fertilizer Over-fertilizing tomatoes early in their lives results in plants that are tall and spindly, with lots of deep green foliage, but few flowers. Tomatoes can't simply use the ideal amount of nitrogen they need to thrive. Instead, excess nitrogen in a tomato plant tells the plant to produce more leaves and stems at the expense of blossoms and fruits. Sometimes, excess nitrogen can be leached from the root area of tomato plants by repeated, deep waterings. Causes of Yellowing Leaves Common causes of yellow leaves on tomatoes include cool soil, age-related death of the lower leaves and a myriad of nutritional deficiencies including nitrogen, boron, potassium, iron and magnesium. Leaves may also yellow when affected by fusarium wilt, bacterial wilt or verticillium wilt. These disease are the result of fungal or bacterial pathogens multiplying rapidly in vascular tissues, causing the plant to die from lack of nutrients. Root knot nematodes can kill plants in a similar fashion, but the roots will bear distinctive swollen knots. Wilts and nematodes are difficult or impossible to treat once plants are severely affected. Soil Solarization Although the disease and pest causes of yellow leaves on a tomato are difficult to cure once the plant is already showing symptoms, you can use soil solarization to destroy these organisms before you plant your next tomato crop. After the troubled tomatoes have died or are removed, till the garden well and smooth the soil with a rake. Apply a 1 mil clear plastic tarp over the prepared and watered soil and leave it there for six weeks. This heats the soil to high enough temperatures to destroy many nematodes and soil-borne fungi and bacteria before the upcoming growing season.
Signs of Too Much Nitrogen in Soil for Tomatoes
Since tomatoes (Lycopersicon esculentum) hate imbalances in soil nutrients, they are prime indicators in the garden when any deficiencies or excesses exist. Adding an overabundance of nitrogen fertilizer can cause abiotic disorders in your tomato crop. These problems, such as low fruit set, result from environmental factors rather than disease or insect pests. Even with all the advancements made in the development of disease-resistant varieties, tomato production can fail because of improper feeding or watering. Absence of Fruit Perhaps the best indication that a tomato bed contains too much nitrogen occurs when the plants produce lush foliage but little or no fruit. Sometimes blossoms also fall off in the presence of excess nitrogen. Early fertilization of tomato seedlings may simply delay flowering and fruiting until some of the nitrogen is washed away. Besides fostering heavy leaf coverage, extra nitrogen causes vines to grow to great lengths with few tomatoes to support. Problems With Fruit When fruit does form on tomato plants, too much nitrogen in the surrounding soil may contribute to some physiological disorders in the tomatoes. Excess nitrogen has been named as a possible secondary factor in the development of blossom end rot. An imbalance of calcium and other soil nutrients leads to this common problem, characterized by a sunken, leathery, dark spot at the blossom end of the fruit. More rarely, a tomato may puff up like a green pepper, with a hollow inside. This can result from applying too much nitrogen fertilizer. Other Effects of Overfertilizing Feeding healthy tomato transplants before flowering and fruit set are well underway can lead to serious consequences. According to the University of California, the full vegetative growth and low fruit set stemming from fertilizer with high-nitrogen content makes tomato plants more attractive to garden pests, like aphids and hornworms. Another hazard of overfertilization is excess nitrogen leaching past the plants' root zone and causing contamination of the groundwater supply far below the surface. Neutralizing Excess Nitrogen If your tomato crop shows any of the aforementioned signs, add a little bonemeal or colloidal phosphate to the soil to balance the nitrogen content. With the proper care, each tomato plant should yield 10 to 15 pounds of fruit over the season. To avoid nitrogen problems from the start, wait to apply fertilizer until after fruit set. Then, following package label instructions, place nitrogen fertilizer in shallow grooves dug around the plants once every four to six weeks, and water well afterward. If you used manure in preparing the planting site, reduce the amount of the fertilizer application by half.