Fertilizer bags have got to be the most confusing things to read. In order to understand a fertilizer we need to first understand the components that make up a fertilizer.
On the front of all fertilizer bags are hyphenated numbers, for example 5-10-5; these stand for the three major nutrients that all plants need for healthy growth. The numbers always appear in the same order and represent the percentage of N, P, and K in the bag.
Nitrogen (N)is the main nutrient and is responsible for new, green foliage. Plants that are mostly leafy, such as lettuce and grass, need plenty of nitrogen for proper growth. That is why lawn fertilizers always have a high first number in the sequence, which represents higher levels of nitrogen present within the bag.
Phosphorus (P),the second number is essential for root growth, development of flowers, seeds and fruit. Bulbs, perennials and newly planted trees and shrubs benefit from high levels of P.
Potassium (K), the third number is responsible for the overall good health of the plant. This nutrient promotes strong roots and stems.
Fertilizers can also contain “trace elements” in small amounts that aid in good plant health. Magnesium (Mg) helps the plant take-up food readily, aids in seed formation and also helps the plant to manufacture its food from the sun. Iron (Fe) helps the plant maintain a dark-green color.
Fertilizers now come in many forms, making the choices of what to use even more confusing. Granular types are applied by using a spreader or by working it into the soil. Water-soluble types, usually powdery in texture and blue in color, are meant to be dissolved in water. Organic types are processed materials such as dried blood, bone meal and manure. Organics have low levels of nutrients compared to the other two, but are the fertilizer of choice with organic growers. Water- soluble fertilizers last up to two weeks before needing a reapplication and can be messy when mixed. Granular is a timed-release lasting longer than the water-soluble kind. Each type of fertilizer has its advantages and disadvantages and the one you choose to use is really a matter of personal preference.
Special blends have been created by the industry to make it easier for consumers to purchase exactly what they need. Flowers require higher amounts of phosphorous, so the bag will have a middle number as high as the first. Lawns need a lot of nitrogen because they are constantly regrowing what has been cut away, therefore the bag will have a higher first number (N). Vegetables are fast growing and need a fertilizer blended almost equally with all three nutrients like 20-20-20. Roses have special needs all their own. Look for fertilizers made especially for roses, as it will contain a unique blend of all three nutrients.
Timed-release fertilizers are becoming popular with gardeners because they release their nutrients over the course of 2, 3, 6 or 9 months (at a soil temperature of 72 degrees). The nutrients are contained within a coated pellet and as the water penetrates the coating, the nutrients inside come out and disperse throughout the soil. Using this type of fertilizer allows the plant to be fed constantly causing less work for you. Timed-release brands are resistant to leaching and will not burn lawns or plants. If you grow a lot of container pots, it would be a great advantage using timed-release as you will only have to feed once during the season, however, make sure you purchase one that will last the correct amount of months for your particular growing season. Because timed-release is based on soil temperatures of 72, it would stand to reason that an increase in soil temperature would speed up the amount of nutrient released. In this case, you can use a water-soluble fertilizer as a supplement to the timed-release so the plants do not miss a feeding so to speak.
Houseplants require the same nutrients as plants grown outside but because the former are grown in pots with limited soil, nutrients are depleted at a much quicker rate so they require a regular fertilizer program. Careful attention must be paid to the amount of N, P, K given as too much nitrogen can cause excessive leaf growth and too little can cause stunted growth. Phosphorous deficiencies cause the plant to experience leaf drop and take on a purplish-blue color. Plants showing sign of leaf mottling, deadened areas near the tips and yellowing leaves are indications of a potassium deficiency. Use a method that is used by many houseplant growers; dilute the water-soluble fertilizer to one-third its normal strength and use this mixture every time you water. Less fertilizer is better than too much.
Greenhouse container crops should be fertilized during the time of active growth, unless you are using a timed-release fertilizer that was added to the pot at the time of planting. Sometimes choices are given on how to measure out the fertilizer, for example, 4.8 ounces of 20-10-20 per 10 gallons of water; pretty straight forward. However, there is a measurement called parts per million (PPM) that you mix with 100 gallons of water. I cannot even begin to explain the details of this, but I can give you the formula to convert PPM to ounces per gallons of water.
Formula To Change PPM Into Ounces Per Gallons Of Water
OK, here we go…
the situation is we have a bag of 20-10-20 and we need 200ppm per 100 gallons of water. Do the following
1.Divide 200(ppm)by 75 which will result in 2.66
2.Change the 20 in the (20)-10-20 to a decimal .20
3.Divide 2.66 by .20
4.The result will be 13.33 ounces of fertilizer to be mixed with 100 gallons of water
5.If you are only going to use 10 gallons of water, divide the 13.33 by .1 (1/10th of 100 gallons of water)
6.The result is 1.3 ounces of fertilizer per 10 gallons of water.
Not So Hard, Right?
Leaching is a practice that should be followed regularly. Excess salts can build up in container pots causing an unhealthy situation for your plants. The salts will show up as a crusty white deposit on the pots surface. Remove these salts by watering the pot thoroughly with plain water, allowing the pot to drain. Wait awhile and water again. Doing this dissolves the salts and drains them from the soil. Leach your pots at least once a month to avoid this problem. Remember, timed-release fertilizers are not affected by leaching.
So now you know what the numbers and letters mean and will be able to decide more easily on what to use.