Liquid Fertilizer

How to choose a liquid fertilizer? Learn to read the labels The attention-getting labels on liquid fertilizer bottles often seem like the latenight TV commercials of the gardening world. Competing with myriad packages on nursery shelves, they make every claim imaginable. In addition to basic nutrients, they tout everything from vitamins to hormones, extracts, and secret formulas supposed to give bigger blooms or better-tasting vegetables.

How do you know what's best for your plants? From fetilizers, plants can receive nitrogen, phosphorus, potassium, and a variety of micronutrients, including iron, manganese, and zinc. Of these, nitrogen is usually the most important, and for a given price, the fertilizer with more nitrogen is a better value.

Here are some guidelines for choosing liquid fertilizers:

When to use a liquid fertilizer

Liquid fertilizers (or their water-soluble dry counterparts) are valuable for a number of reasons. First, being water soluble, they allow you to get the nutrients down into the root zome--even of established plants--where they are needed. For even quicker uptake of nitrogen and micronutrients, they can be used as foliar sprays. You can apply small quantities of liquid fertilizer with greater precision than you can with dry fertilizer. Dilutions can be easily increased for more frequent, light feedings. Liquid fertilizers are also easy to use and to shore.

Their minus side is that, for large areas like lawn's and vegetable gardens, the are often difficult and usually uneconomical to apply. In such cases, dry fertilizers are aetter buy and easier to use. Also, since all liquid fertilizers are made of dissolved salts, they are more likely to cause leaf burn if you apply too much.

The primary nutrients: it's nitrogen

Concentrations of primary nutrients--nitrogen (N), phosphorus (P), and potassium (K)--are expressed in the N-P-K percentages listed on a fertilizer label. For example, a 10-10-5 fertilizer label. for example, a 10-10-5 fertilizer contains to percent nitrogen, 10 percent phosphorus, and 5 percent potassium.

Manufacturers often sell fertilizers with certain ratios of nutrients for use on specific types of plants. For instance, mixtures with low percentages of N compared to P and K are often sold as flowering plant food. This is usually done to give the product a unique identity but will have little effect on plant growth.

Of the three primary nutrients, only nitrogen leaches through the soild and needs to be replenished regularly. In fact, most forms of phosphorus and potassium do not move vertically through the soil the way nitrogen does. Instead they are fixed in the top 2 to 3 inches of soil.

By comparing percentage of nitrogen per volume of liquid, you can evaluate the relative cost of two products. For instance, a 16-ounce bottle of 10-2-2 fertilizer contains twice the nitrogen as the same-size bottle of 5-2-2. All other things being equal, it should be twice the value.

The type of nitrogen (listed in the guaranteed analysis on the label) a liquid fertilizer contains may also influence which products you buy. Most liquids contain nitrogen in either ammoniacal or nitrate form, or both.

Ammonical nitrogens, which include urea, are released slowly to plant roots depending on soil temperature, microbial action, and concentration of roots in the container. They also have a gradual acidifying effect on the soil.

Nitrate forms of nitrogen are immediately available to plant roots and are leached quickly through the soil. To give a plant a quick boost, especially if it's growing in cold soils, nitrate forms are best. For acid-loving plants or maintenance feeding, ammoniacal forms may be better.

Fish emulsion is a liquid, organic form of nitrogen that is also released slowly to plant roots. How fast it can be used depends on soil temperature and microbial action.

When do plants need micronutrients?

The last five years have seen a great increase in the number of fertilizers containing micronutrients, particularly iron, zinc, and manganese. This is probably a result of the increasing popularity of container gardening and the lack of micronutrients in some potting soils.

Most garden soils contain enough micronutrients for healthy plant growth. It is not necessary to apply them unless plants are showing obvious signs of deficiency.

If your container plants are not rich green despite regular applications of nitrogen fertilizer and proper light exposure, select a liquid fertilizer containing chelated micronutrients. Chelating agents hold micronutrients in a form which makes them most available to the plant. They can also be applied effectively as foliar spray.

Seaweed extract is an organic fertilizer that is a source of micronutrients, although it is often expensive.