How to Fertilize a Vegetable Garden

Root crops require different fertilizers than leafy crops.

If you've taken the time to plant a vegetable garden, there's little doubt you want the highest yield possible from that garden. Most gardeners believe that frequent fertilizing is the best way to achieve this...But is it?

Easy Does It
First, let's talk about why fertilizer - organic or synthetic - can be a bad thing: Fertilizers contain salt. Just as too much salt is bad for humans, too much is deadly for plants, also. Salt kills fruits and vegetables by blocking their ability to absorb the water and nutrients they need to survive. The first sign of salt death is slow growth. Then the plants begin to wilt and turn yellow. Finally, they die an untimely death. So remember: Too much fertilizer = plant death.



Soil Type
Soil type plays a huge role in how often fertilizer is needed. If, when you irrigate, the water disappears quickly, you'll need to fertilize more frequently than if the water sits in the soil for a long time. In addition, adding nutrients to the soil that are not needed causes a soil imbalance, which can lead to serious gardening difficulties - so testing your soil is vital before fertilizing. Finally, vegetables and fruits grown in pots will need more frequent fertilization than those grown directly in the earth.

Corn and tomatoes require more fertilizing than most other crops.

Crop
What sort of plants you are growing also determines how often you'll need to fertilize. Some plants are "heavy feeders," consuming more nutrients than others. Tomatoes and corn, for example, are very heavy feeders and therefore need more frequent fertilizing than, say, lettuce or peas.

Choosing Fertilizers
All commercially sold fertilizers are labeled with a ratio telling gardeners how much nitrogen (often abbreviated "N"), phosphate ("P"), and potash ("K") are in it. For example,  for every 100 pounds of a 5-10-5 fertilizer you purchase, you get 5 pounds of nitrogen (the first number), 10 pounds of phosphorus (the middle number), and 5 pounds of potassium (the last number).

The wrong kind of fertilizer will make tomato plants fruitless.

Generally, where leafy top growth is desirable (like with lettuce and corn) you'll want more nitrogen than root crops like carrots. (Although if you like to eat the green tops of root crops, you may wish to give them as much nitrogen as leafy crops.) On the other hand, phosphate promotes root and fruit production and potash encourages hardiness and durability.

Probably the most misused fertilizer is nitrogen. Many gardeners lavish it on their vegetables and fruit, but it can easily result in lots of leaves - and not much else. For example, potatoes over-fertilizes with nitrogen have lots of leaves, but not many potatoes, and tomatoes, too, can end up with tons of leaves but no fruit.

One of the reasons for the over-use of nitrogen (and other fertilizers) is that many gardeners expect instant results. However, it takes about three or four weeks for fertilization to "kick in."

Finally, consider whether you want to use organic or synthetic fertilizers. The choice may seem obvious, especially once you know that organic fertilizers help create the microbiological growth that supports good soil structure and helps retain water and nutrients in the soil. (Synthetic fertilizers do not.) However, organic fertilizers vary widely in what nutrients they provide, especially if they are not commercially packaged. Certain organic fertilizers (especially  manure) are also higher in salt.

Fertilizing the Vegetable Bed
If your garden bed is imbalanced, fertilize according to the missing nutrients. For example, if your soil test revealed your garden is low in potash, you'll want to mix a fertilizer high in potash into the soil before planting. For the rest of the gardening season, use a fertilizer that's high in potash.

If a soil test reveals your soil isn't lacking in any area and you still want to fertilize, here's a good way to proceed, according to the Colorado State University Extension Office:

Leafy vegetables like lots of nitrogen.

1. Apply "small amounts of a nitrogen-only fertilizer several times during the growing season." First, before planting (mixing it into the soil with a spade or rototiller); use up to 1/2 pound of nitrogen per 1,000 square feet." Water in.

2. "Every four to six weeks, apply a nitrogen fertilizer such as ammonium sulfate (20-0-0) or bloodmeal (15-1-1) at the rate of no more than 1/10th pound of nitrogen per 100 linear feet of row."

Other Extension Offices (like the University of Connecticut Extension Office) recommend using a balanced fertilizer - that is, one that has equal amounts of N-P-K. For example, a fertilizer marked 8-8-8. A fertilizer that is nearly balanced (like 8-10-8) works, too.

Make Your Own
Now that you know how to fertilize, you may run to the gardening center and...experience sticker shock. So here's a how to on how to make your own fertilizer.

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