Garden Variety: Increase fruit, vegetable yield with the right fertilizer

Choosing the right fertilizer for the garden and applying it properly can increase yield of fruit and vegetable crops. Done incorrectly, it can be a waste of time and money. The hard part is knowing what and how much is needed, and a look at the options only makes the task more daunting. A little understanding of what plants need can maximize yield without breaking the bank.

The use of fertilizer is a way of providing nutrients to plants when soils are deficient or when adding more nutrients can increase yield. For example, tomato plants that are fertilized may produce more tomatoes than would otherwise. There is a limit to how much benefit fertilizer can provide, though — add too much and the plant will only produce leaves or could even be killed.

Most garden guides and experts will tell you to have a nutrient analysis done on the soil before fertilizing. If you are interested in soil testing, K-State Research and Extension offers low-cost testing through the KSU lab. Samples can be submitted through county offices to save on shipping. There are also some private labs that do testing. Many garden centers sell home testing kits also. If you purchase one of those, look for ones that give ranges of nutrient content in parts per million (ppm) instead of giving arbitrary references such as high, medium and low.

Most people forget to do this when they need to, and it seems much simpler to pick something up and take their chances. That is OK, too, but this is the part where a little caution is needed.

There are a lot of options for fertilizer — tomato food, rose food, all-purpose food, organic options, liquid vs. granular, and slow vs. quick release. Some contain only one kind of nutrient, some are a balanced mix, and some contain micronutrients.

All fertilizer is required to have the nutrient ratio listed on the container. This is displayed as three hyphenated numbers, such as 12-0-0, 10-10-10, etc. The three numbers represent the percentages of nitrogen, phosphorus and potassium, in that order. The rest of the product is carrier, filler or coating.

This is where price differences are most apparent. A fertilizer with more nutrients will typically be more expensive than one with low nutrient content, but it will provide more for the money also.

Nitrogen levels fluctuate often in the soil and are easily tied up in chemical processes, so additions of nitrogen often benefit fruit and vegetable plants.

In northeast Kansas, soils often have more than enough phosphorus and potassium to sustain plant growth and provide for good yield from crops. Unless you have a soil test indicating that your soil is deficient in one of these nutrients, assume your soil has enough already.

The other nutrients necessary for plant growth are rarely deficient and also should only be added if indicated by a soil test.

To apply nitrogen during the growing season, the best option is to use a liquid product or a method called sidedressing, where granular fertilizer is placed in the soil alongside the crop row or around the root area of the plants. The rate and timing depends on the crop.

Choices about liquid vs. solid, organic vs. inorganic and slow-release vs. quick-release are a matter of personal preference or may be tied to the product of choice.

Organic fertilizers are generally from plant or animal sources. Gardeners may choose organic because of personal preference, dietary concerns and concerns about the manufacturing process of inorganic fertilizers. Vegetarians and vegans may wish to be extra-selective about fertilizers from animal sources, such as blood meal.

Slow-release fertilizers break down over the course of the season, providing a slow stream of nutrients for a long period. Most organic fertilizers are considered slow-release. Inorganic fertilizer may be coated with inert material to promote longevity. Quick-release fertilizers are readily available to the plant and may show almost immediate effects.

If this still sounds confusing, check out the K-State Research and Extension guide “Fertilizing Gardens in Kansas,” available on its website,, or through local county offices.

One last thing gardeners often ask about is lime. Lime is not a fertilizer but is often found alongside fertilizer. It is a mineral that raises soil pH.

If soil is acidic, lime benefits the soil by raising the pH to a more desirable level for plant growth. In home gardens in northeast Kansas, soil pH tends to be high already. Adding lime to soil with a high pH makes the situation worse instead of better and is difficult to reverse.

This is one case where testing the soil is vital before application. Get a home test kit if sending a sample off is too much work. If the pH is very low, lime can be applied to bring it up. If the pH is high, sulfur can be applied to bring it down. Consult with a professional for amounts and application methods.

— Jennifer Smith works in regulatory horticulture and has worked as a horticulturist for various government entities. She has experience in landscape design and maintenance and as an educator.


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