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How to Choose the Best Plant Fertilizer

Today I want to teach you how to choose the best vegetable fertilizer for your plants and what the numbers on fertilizer mean.

Have you ever stood and looked at the plant fertilizer shelf and had no idea what one to choose? I have. It can feel very overwhelming. Here are some tips I have learned about how to choose the best fertilizer for each one of your vegetables, herbs and flowers.

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What do the Numbers on Fertilizer Mean?

Most plant fertilizer is labelled with three numbers on the container. (As is this fertilizer from Amazon.)

Before knowing what fertilizer to select for our vegetables we need to understand what each of the numbers on the fertilizer means. The first group of numbers is the nitrogen percentage, the next phosphorus and the third group potassium (or potash). Knowing that still doesn't help unless we understand how each nutrient effects our plant. Think of it this way, nitrogen = leaf production, phosphorus = root growth, potassium = flower/fruit production. Look for a fertilizer with the highest number being where you want to see the most concentrated plant growth.

Use this chart to figure out what the best fertilizer for vegetables is and what the numbers on fertilizer mean.

For example; for lettuce, spinach, cabbage and anything leafy you may want a 20-5-5 plant fertilizer (maximizing leaf production). For carrots, potatoes and beets a 5-20-5 plant fertilizer (maximizing rood growth). And for tomatoes, peppers, squash and cucumbers, your "fruit" bearing plants, a 5-5-20 plant fertilizer (maximizing flower and fruit production).

The above examples may be extremes. We do want to keep the whole plant healthy so choosing a fertilizer with higher numbers in all three categories with a slight leaning to where you want to focus most gives you the best option. The only vegetables that I fertilize with more than compost are my tomatoes, peppers, squash and cucumbers as this gives them a boost with our short growing season and encourages more fruit production. For these I use a 18-18-21. Other vegetables tend grow well and produce without needing that boost as long as you have healthy garden soil mixed with a quality compost. The best fertilizer for annual flowers is 20-20-20, helping them grow to their full potential and producing many flowers during our short growing season. These fertilizers need to be mixed with water prior to applying. Follow the package directions for diluting.

How Often should I Fertilize?

How often you fertilize your vegetables and flowers depends on how quickly and how much you want your plant to produce and grow. I suggest fertilizing vegetables every 3 weeks and flower every week, but even fertilizing once a month will be enough to notice an improvement in your plant growth and production!

Don't ever fertilize very dry plants. This will cause burning of the roots because of the high nitrogen levels in the fertilizer. If they were watered the day previously and aren't drooping you should be good to go.

Organic Fertilizer

There are also options of using other plants and weeds to make an organic fertilizer type "tea" by putting them in a bucket with water and allowing them to sit and "steep" for a few days. By choosing plants with leaves that are high in nitrogen, potassium and phosphorus you are able to return these nutrients directly to your plants through the tea water. I have noticed my plants benefit from this fertilizer tea. Learn how to make it here.

Learn how to make homemade organic DIY plant fertilizer using these tips.  Make your own homemade vegetable fertilizer!

Lets not forget compost as fertilizer! It is your most basic type of plant food, containing various amounts of beneficial nutrients. A good compost alone will provide enough nutrients for fast growing veggies like carrots, potatoes, beets and onions. If you want to learn more about composting read my 6 Compost Tips.

I hope this information was easy to understand and helps you feel more confident next time you go to pick up a plant fertilizer!


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Good morning! I have started some seeds in the Sungro sunshine mix. When should I fertilize them and do I use full strength? I love your blog and find it so informative and useful. Thanks Penny


What are your thoughts on coffee grounds in the garden? I find conflicting information. Some say put it with peppers and tomatoes, some say it will stunt their growth.

Krista Green
Krista Green
Jan 24, 2022
Replying to

I do mix my coffee grounds in with my compost. If mixing in with soil in peppers and tomatoes just go easy on amount. Not more than 2 Tbsp per plant. I have not noticed that it has stunted growth but now I may have to do a comparison project with them!

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