For the novice gardener, it’s important to understand that all garden plants have feeding requirements. Although most soils contain a reservoir of essential nutrients, the levels of one or more readily available nutrients may not be at a sufficient level to sustain optimum plant growth. The other consideration is that vegetable plants vary in their total nutrient needs. Sweet corn, for instance, requires 140 lbs. of nitrogen (N) per acre whereas radish needs between 60 to 70 lbs. N per acre. Don’t worry, on most bags of fertilizer, application rates are usually expressed in easy-to-understand units based on feeding a single plant or on a plant-row basis.
The most important elements which are considered critical for good plant development and productivity are recognized as macronutrients as N, P, K, Ca, Mg and S and micronutrients (trace elements) such as B, Mo, Fe, Zn, Cu and Mn. The main difference between these categories is in the amounts taken up and utilized by garden plants. Macronutrients are taken up in larger quantities than are micronutrients. However, and regardless of their category, each element plays a critical role in the plant’s health and development.
There are only a few key items one needs to know in order to properly use fertilizer. These are: 1. Know how much fertilizer a particular vegetable needs, 2. Know which nutrients are abundant and which are lacking in your garden, and 3. When should fertilizer applications be made. As I mentioned in an earlier post, pH and Soil Amendments, having a soil test performed is an excellent way to gain insight into the nutrient levels and pH of your garden soil. Additionally, most soil test results will also include fertilizer recommendations of up to three crops.
Regarding the nutrient needs of 100 fruit and vegetable plants, is a considerable amount of data and is not feasible to display in this post. However, I will share a reference that should more than satisfy your needs. This comprehensive document covers various vegetable crops and addresses fertilizer rates for both macro- and micronutrients.
What’s in a Bag of Fertilizer?
The first item which needs to be learned is how to interpret what’s in a bag of fertilizer. As many of you perhaps already know, all fertilizer products follow the same designation system regarding the quantity of key nutrients found inside a bag. This is true for both conventional and organic based fertilizer. To help explain this in a bit more detail, I’ve provided an image of a fertilizer bag containing soluble/available forms of nitrogen (N), phosphorous (P) and potassium (K). Since this formulation was created specifically for tomato plants, it also contains 2% Ca, however, it isn’t listed on the front panel. Without an adequate supply of available calcium, the tomato crop will likely succumb to a physiological disorder called, blossom-end rot.
The 4-3-3 designation tells us that this bag contains 4, 3 and 3% of plant available N, P and K. In this instance, this bag weighs in at 5 lb. of total fertilizer (elements plus inert material). So, in the case of nitrogen, 5 lb. of fertilizer multiplied by .04 (4 %) = .2 lb of nitrogen. If you were required to apply 1.0 lb. of nitrogen to a 20 ft. row of okra, you would need to acquire 5-bags (25 lbs.) of fertilizer and spread the entire contents in said row. However, should your soil test results indicate that your soil already contains healthy levels of available P and K, then you’d be better off to search for fertilizer with a greater portion of N and less P and K (e.g., 20-2-2).
How Do I Apply Fertilizer?
There are three basic ways to apply fertilizer in the home garden; 1. Broadcast granules, 2. Incorporate granules and/or 3. Foliar feed. In most cases, I prefer soil incorporation of all required nutrients with the exception of broadcasting in certain scenarios. I am not fan of foliar feeding.
Broadcasting Granular Fertilizer
There are certain occasions when broadcasting fertilizer is called for. For instance, you may have an area in the garden which will be dedicated to establishing a certain crop that has nutrient requirements unlike the rest of the garden. So, let’s say it’s a potato crop, and the soil test recommends a preplant application of 5 lbs. of 10/10/10 in a 1,000 sq. ft. area. Weigh out 5lbs. of fertilizer and apply a uniform amount over the 1,000 sq ft area. Once completed, I highly recommend a light raking so that the fertilizer is somewhat incorporated in the soil.
Some gardeners may elect to broadcast fertilizer to row crops as well. For instance, in a row of beans, you might apply fertilizer on top of the soil (in the furrow) next to your plant row. However, I can’t say I agree with this method as you are bound to lose valuable nutrients to runoff and evaporation. The other scenario that calls for broadcasting fertilizer, without the opportunity of incorporation, is for beds of strawberries, asparagus, etc. For obvious reasons, you are now forced to broadcast fertilizer over the tops of plants.
Incorporating Granular Fertilizer
This is by far the most accurate means of delivering the intended quantity of fertilizer to your plants. For beans, corn, okra, eggplant, beets, etc., this is the preferred method (IMHO). Prior to applying fertilizer, I use my hoe to make a small trench in the soil approximately 1 to 2 inches deep and about 2 to 3 inches away from the base of all plants. Your digging should not disrupt the roots! Evenly apply the fertilizer in the trench and cover the fertilizer with soil immediately thereafter.
Foliar Feeding with Fertilizer
Although I am not a huge advocate of foliar feeding, it does have a few redemptive qualities. In some instances, a foliar feed for the specific use of delivering micronutrients (Boron, Manganese, etc.) to a plant can prove beneficial. This would certainly be the case if your soil test had called for the application of these elements, yet you didn’t apply them preplant. Additionally, some gardeners use foliar solutions of Calcium to spray on tomatoes to prevent the incidence of blossom end rot.
Thank you for taking time to look this over and I surely hope that you will share your comments and experiences with us.