Fertilizing Your Vegetable Garden

Question of the month: I read a lot of different opinions on fertilizing my vegetable garden. What do Collin county master gardeners recommend I do regarding fertilizing my vegetable garden?

There are several different approaches to fertilizing your vegetable garden. Collin County Master Gardeners are research-based gardeners who work with the Texas A&M AgriLife Extension Service and follow tested and proven gardening methods. For decades the common practice has been to fertilize the plants and not spend much energy working with the soil. Over time more and more fertilizer is needed to get a good yield from the garden. While this approach certainly works, research now shows the quality of the soil is very important in growing plants and having a healthy garden in the long run. Let’s see what the research now shows…

To begin with, what nutrients do vegetables need to grow? Plants need sixteen elements to grow normally and be healthy. They are either considered macronutrients (needed in large amounts) or micronutrients (needed is smaller amounts). The macronutrients include carbon, hydrogen and oxygen, and these are found in water and air. Other macronutrients include nitrogen, phosphorus, and potassium and are found in the soil. Secondary macronutrients which are also found in the soil include calcium, magnesium, and sulfur. The micronutrients are all found in the soil. They are boron, chlorine, copper, iron, manganese, molybdenum, and zinc. We can already see if we only use commercially available complete fertilizers, we are only getting three of the thirteen elements found in the soil which are needed for healthy plants. Over several seasons, if the soil is not amended, the plants will consume most of the nutrients in the soil. Complete fertilizers only address the shortage of nitrogen, phosphorus, and potassium. Research now shows that the most effective and economical way to address the remaining nutrient shortage is to add organic material to the soil on a regular basis. The regular addition of organic material will slowly add all thirteen of the nutrients to the soil.

Of all of the types of organic material, research continues to show that compost is the best soil amendment. Compost is produced when once living organisms break down through the natural process of decomposition. The result of this decomposition is a nutrient rich, crumbly, soil like material. There are many benefits to using compost:

1. Because the material breaking down (leaves for example) was once a living organism, it contains the nutrients plants need to grow.
2. Compost improves the structure of the soil allowing the soil to maintain the nutrients gained.
3. Because the decomposition process is slow, the nutrients are released slowly.
4. Compost changes the structure of the soil. In sandy soils this means the organic material will bind with sand particles and as a result enable the soil to hold more moisture. In clay soils, prevalent in our area of North Texas, this means the organic material will bind with clay particles creating space which allows water to drain better and for roots to spread more freely.
5. The decomposition process increases microbial activity in the soil which has been shown to be a very positive activity for the soil.
6. And lastly, using compost decreases the waste that goes to landfills.

We now see the combination of using fertilizer and adding organic material to the soil on a regular basis will keep the thirteen elements (not counting the three elements received from water and air) needed for plant growth in the soil and available for the plants to use.

With this knowledge, let’s go to your garden. The first thing to do is to have a soil test done. This will tell you which nutrients are available and which ones are not. You can send a sample of your soil to your local county extension office for a detailed testing. The big box stores also sell very basic soil testing kits. You should have your soil tested every three years or so. The test results will show if you have any nutrient deficiencies. If you have any nutrient deficiencies you will now know whether you can continue to use a complete fertilizer or if you need to use an incomplete fertilizer. A complete fertilizer has all of the big three macronutrients (nitrogen, phosphorus, and potassium). An incomplete fertilizer is missing one or two of the macronutrients listed above and is a good choice for correcting nutrient imbalances. It is worth noting that our clay soils here in North Texas are generally nutrient rich. The problem is the nutrients are locked up and hard to use because of the structure of the clay soil. You may find you only need amendments to free up the nutrients in the soil (see paragraph above on compost). For more information on buying fertilizer, fertilizer selection, the proper use of fertilizer, and methods of applying fertilizer I suggest reading the following article “Fertilizing a Garden.” You can find the article at https://agrilifeextension.tamu.edu/library/gardening/fertilizing/.

Regardless of the soil test results you should come up with a plan to put organic material into your garden on a regular basis. You can use compost which is the best soil amendment. You can buy compost from the local nursery or make your own. If you want to make your own, I recommend you read the following article to get started; https://agrilifeextension.tamu.edu/library/gardening/composting/.

You can also use mulch which is organic material that will break down over time and become compost. For more information on using mulch, I recommend you read the following article to get started; https://agrilifeextension.tamu.edu/library/gardening/mulching/. Be aware that if you use mulch, the microbes which break the organic material down will consume available nitrogen which is in the soil. Think of mulch and compost this way. Mulch breaks down and becomes compost. Compost breaks down and releases nutrients into the soil.  

Something else to consider in a vegetable garden are the plants themselves. Vegetables are considered to be either heavy feeders, light feeders, or soil builders. Heavy feeders use a lot of nutrients during the course of the growing season and benefit from additional fertilizer at the time of planting and another application during the peak growing period. Light feeders benefit from the application of a small amount of fertilizer at planting time. And soil builders, aka nitrogen fixing plants, get their name from the fact that these plants actually put nitrogen back into the soil. Below is a partial table grouping vegetables by the type of feeder they are. Do your research before planting and determine what category your vegetable falls into.

HEAVY FEEDERS

Asparagus               Celery                              Kohlrabi                        Rhubarb

Beets                       Collards                           Lettuce                         Spinach

Broccoli                   Corn                                 Okra                             Squash

Brussels sprouts     Cucumbers                       Parsley                        Strawberries

Cabbage                 Eggplants                         Peppers                       Sunflowers

Cantaloupe             Endive                              Pumpkins                     Tomatoes

Cauliflower              Kale                                 Radishes                      Watermelons

 

LIGHT FEEDERS

Carrots                    Mustard greens                Potatoes                       Swiss chard   

Garlic                       Onions                             Sweet potatoes            Turnips

Leeks                       Parsnips                          Rutabagas                    Shallots 

 

SOIL BUILDERS

Alfalfa                      Snap peas                           Peanuts                         Southern peas

Broad Beans           Clover                                  Peas                               Soybeans

Lima beans

There is nothing like going out to your vegetable garden and seeing your hard work result in healthy and tasty vegetables. To recap, to help you get there Collin County Master Gardeners recommend regular soil testing and the correct use of fertilizers. We also recommend each gardener have a plan for adding organic material to their garden on a regular basis. And lastly, take the time to do a little research and know what your vegetables need to grow, to be healthy, and ultimately taste good at dinner time.