Whether you decide to grow organically or not, or somewhere in between, the very best thing you can do for your edibles is feed the soil and let the soil feed your plants. Supplemental fertilizer is needed for specific plant types at specific times, so you do need to get to know the needs of your plants. Here we will focus on tomatoes.
Before you plant your first tomato, hopefully you have made some basic decisions about your soil, and incorporated amendments to improve the soil as necessary. A simple soil test kit can help you determine deficiencies in the soil as well as pH.
Soil pH is important when growing edibles. Tomatoes will grow and produce even in poor soil, but for a good harvest and great flavor tomatoes will not only need some basic soil nutrients, but a slightly acidic pH of about 6.2 to 6.8, but will do fine in a range of 5.8 to 7.0. Most regions typically have fairly neutral soil and it would be somewhat unusual if you find your soil to be dramatically alkaline or acidic. But if you have not had good performance with tomatoes, do check the pH.
Since tomatoes are heavy feeders, you will need to supply nutrients throughout the growing season. There are specific times in the plant development that specific nutrients will benefit your tomatoes, but until you learn the sources of individual organic nutrients, as well as the speed of delivery, it is best to use premixed balanced fertilizers.
Generally a balanced fertilizer with nitrogen, phosphorous and potassium is recommended until you gain experience with applying nutrients individually. Several options premixed for tomatoes and vegetables are readily available at garden centers. I like a 10-10-10 early in the season and a 5-10-10 once the fruit sets. And for ease of use I suggest granular rather than liquid.
At planting time a granular fertilizer can be mixed into the soil, or organic amendments can be used. A bit of a quick release as well as a slow release amendment can both be added.
As plants begin to establish and grow, additional fertilizer can be applied in granular form as a side dressing. Side dressing is simply sprinkling the fertilizer on the soil surrounding the plant without contacting the plant. Create a shallow furrow by running your finger in a circle around the plant in the drip line. Sprinkle in the fertilizer and push the soil back over it. Rain or watering will slowly release the nutrients to the root zone.
Early in the season when the plants are getting established and growing very actively, they will consume more nitrogen. Be aware too much nitrogen can encourage too much foliage growth and inhibit the development of blossoms and fruit. Alfalfa meal is a good quick release nitrogen .
When blossoms and fruit are developing your tomatoes will need more phosphorous and potassium. Kelp meal is a good source of potassium
As fruit develops never over apply fertilizer. Encouraging fast growth can cause cracking. Side dress with a 5-10-10 fertilizer about every three weeks, carefully applying according to package directions. That should be about a tablespoon or two per plant spread evenly around the plant in the drip line.
What type, brand, amounts and frequency of fertilizing has long been debated by gardeners and it seems that every gardener has a different opinion about what works best. But of course every gardener has a little different soil, different amendments added over varying years of use, etc. etc. The point is, like everything with gardening you will need to experiment a little and learn by trial and error. At your garden center I am sure that you will find liquid or granular, chemical or organic, general vegetable or tomato specific, as well as a wide variety of natural amendments that provide single nutrients or minerals. Don’t worry! Pick something that seems right for you and get started. I know your tomatoes will be delicious no matter which brand or type of fertilizer you use.