Thursday, May 28, 2009

Horticulture Professional Answers Fertilizer Questions

This is an e-mail I did with horticulture professor, Dr. Paul Thomas on fertilizer. He co-taught my horticulture and greenhouse management class last semester. Hope this answers some of your questions on the topic.



What fertilizer is best for plants in the summer months?


The best fertilizer for your garden plants in summer is happily the easiest to come by. Granular fertilizer with an N-P-K analysis of 10-10-10 or 8-8-8 will work great for vegetables, shrubs, young trees and flowers. The only time you need special fertilizers are when fertilizing azaleas, rhododendrons, and other acid-loving plants. For these plants, an acid-forming fertilizer is best.


What is the best way to apply this fertilizer?


Fertilizer application may seem easy, but we kill a great many young plants by spreading it improperly. First, follow the label or bag rate recommendations to the letter. The detailed recommendations are there for a reason. Fertilizers are all very different and you need to pay attention to how much is recommended. Secondly, when spreading the fertilizer, keep it off foliage and stems. Be especially sure not to allow small piles of fertilizer form up against stems. This is almost always fatal. Keep the fertilizer at least an inch away from stems. Thirdly, always water the plant after fertilizer to wash off the fertilizer dust from the leaves and to being the dissolving process that allows the plants to take up the fertility. Failure to do so yields burn damage on leaves and dessicated, shriveled stems. Fertilizer burn can also be an entry pathway for plant disease.

How often should you apply fertilizer?

For most vegetable, flower and shrubbery plants, applying fertilizer every three weeks during the growing season is the most you would ever do. Trees and shrubs do not need to be fertilized after the spring flush of growth is over, usually by the first week of July. Flowers and vegetables grow continuously, and there for need a steady source of fertility. You can usually stop fertilizing flowers and vegetables in August. Remember that over-fertilization can reduce flowers and sometimes retard growth in vegetables and flowers.

Should different fertilizers be used in the cooler months?


If you live in the south, where pansies, dianthus and other cool crops such as broccoli, kale and cabbage, can be grown all winter, a fertilizer that is high in nitrate is best. Summer fertilizer usually is a mix of ammonium and nitrate, which together forms (no surprise) ammonium nitrate. In winter plants have problems taking up ammonium, so sticking with nitrate only fertilizer products is recommended.

Is it safe to fertilize vegetable plants? Is there a stopping pointfor fertilizer application prior to harvest? If so, how long?


Because most vegetables grow continuously during the entire summer, it is safe to fertilize on a steady schedule. However, once a plant has produced nearly mature fruit or vegetables, you should consider backing off the amount of fertility. In general, most common garden vegetables can be allowed to grow without additional fertility by the first week in August. Alternatively, applying half the rate to plants such as indeterminate tomatoes will keep the plants strong until first frost.





2 comments:

  1. Is it safe to spray vegetable plants with a mixture of water and ammonia to rid the slugs? Have never had a problem with them until this year and I'm constantly killing them now on a daily basis. They even ate my potted plants on my front door-step! Thank-you very much. Angela

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  2. Angela,

    I'm not sure, but I have e-mailed Dr. Thomas, a horticulture professional from the University of Georgia, and as soon as he responds I'll post that to the blog. Thanks for the comment!

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