When it comes to fertilizing I get asked what I personally use for the nursery and for my own plants. The answer is both simple and complex depending on the plants and if I forgot to fertilize.
Fruiting Perennial Plants - Espoma Organics Citrus Tone
Annual Fruit, Vegetable, and Herb Plants - Espoma Organics Garden Tone
Cactus and Succulent Plants - Espoma Organics Plant Tone
Flowering Plants Both Annual and Perennial - Espoma Organics Flower Tone
Added Fertilizers For Occasional Use - Fish Emulsion, Morbloom, Iron Fertilizer, Bat Guano, and Manure Tea.
1. For Tropical Fruit Trees, Dragon Fruit, and Regular Fruiting Plants I prefer using Espoma Organics Citrus Tone, when planted in the ground you can follow the instructions listed.
Though I recommend that fertilizing is completed 3x a year for optimal growth and fruit set, the three dates I like to give to out for remembering to fertilize are Harvest Day/Halloween, Christmas/New Year, and Valentines Day. These three dates are easier to remember and will help give your fruiting plants the energy that they need to set and maintain fruit.
For plants that are container grown I always recommend a different approach which is monthly fertilizing. Each plant is going to need a different amount of fertilizer and I always water it in after sprinkling it into the pot. #1 Pots add just a small pinch of fertilizer. #5 Pots add 1 teaspoon of fertilizer. #15 Pots add 1 tablespoon of fertilizer.
2. When it comes to annual fruit, vegetable, and herb plants I use the Espoma Organics Garden Tone, personally I use it monthly, waiting at least one month after transplanting before using. Using a measuring cup when spreading it out into rows and garden beds by following the instructions listed.
Though for container grown plants I will use a 1 teaspoon of fertilizer per #5 Pot and 1 tablespoon of fertilizer per #15 Pot, for larger pots such as 30 Gallon Containers I use 3 tablespoons of fertilizer or a equivalent of 1 tablespoon per 10 Gallons of Soil.
3. For my cactus and succulents, as well as hedges, and other plants which aren't flowering or fruiting I like to use Espoma Organics Plant Tone. As previously mentioned you can follow the instructions on the bag for plants planted into raised beds or in the ground.
As for those grown in containers, remember to fertilize every few months, using just a pinch for plants in #1 Containers, 1 teaspoon for those in #5 Containers, and 1 tablespoon in #15 Containers. These plants typically don't need as frequent watering and fertilization as others, which is why I don't fertilize as often.
4. Flowering Plants do typically use up a good amount of nutrients whether in the ground or in pots. You can utilize the Espoma Organics Flower - Tone for all sorts of flowering plants (typically I don't use it for Camellia, Gardenia, or Azalea's as those need more acidic fertilizer and nutrients). Follow the instructions for in ground and container plants.
For container plants I do recommend that all flowering plants are fertilized monthly with a pinch for small plants, 1 teaspoon for #5 Container plants, and 1 tablespoon for #15 Container plants.
5. A nice added fertilizer I use on occasion is the Fish Emulsion, it is a great fertilizer to mix and water with 1-2x a year for all of your potted plants and gives them a nice little boost when done in February - March and then again in June. Its especially great for veggie and fruit gardens and has really helped me to have larger fruit sets when used a few times during the growing season.
6. Morbloom is a fantastic liquid fertilizer I have used for clients when taking care of their roses, geraniums, and other flowering plants. They see overall happier plants, more blooms, and sometimes even longer blooming periods when it is utilized. Its great for both in ground and potted plants.
7. Chelated Iron Fertilizer is a great additional fertilizer to use to water with, though I tend to use it mostly for potted plants and in addition to the fish emulsion for my fruiting plants and even veggie garden.
8. Bat Guano is a product I have had clients ask me to use with their gardens and plants and I have seen some success with it in the general health and size of the plants.
9. Manure Tea is something that you can make at home on your own, utilizing either steer or horse manure in my experience, I have both made and used it in the past with great results in addition to the Garden Tone and Iron/Fish Emulsion for past veggie gardens. When using make sure that you really water in the plants well and you can use the remaining remnants of the tea to compost.
A few tips worth mentioning.
Never fertilize a plant that has been transplanted within the last month, despite some mainstream gardeners and growers saying it is ok. Its one of the easiest ways that you will see your roots burn and sometimes even stunted root/growth of your plant. By waiting a month after transplanting you give your plant a higher chance of success and some time to adjust after the initial transplant shock.
Water after fertilizing even if the instructions say that you don't need to. This helps to start the breaking down of the materials in the fertilizer while also spreading out the material of the fertilizer. Personally I like to deep water after I fertilize for the best results.
In ground plants should be fertilized 2-3 times a year and most potted plants should be fertilized monthly if they are flowering or fruiting types.