Soil Improvement

Nitrogen deficiency on turnip leaves

I have tested the soil in several areas of Globe-Miami, and the results all come back exactly the same. The tests show no available nitrogen, no available potash, the phosphorous content is so high it's off the scale and the pH is 9. Lets take these one at a time.

Nitrogen is the plant food that all green plants must have to be able to make chlorophyll, which is what makes them green. Nitrogen exists in the air as a gas. Certain types of plants called legumes (peas, beans, clover, alfalfa and some trees like mesquite and locust) can have a symbiotic relationship with a class of bacteria in the soil which captures nitrogen from the air and converts it to a form plants can use in the soil. Several organisms are capable of nitrogen fixation, the ones most commonly associated with plant roots are the Rhizobia. Scientists have been able to isolate and grow the Rhizobia bacteria that is best adapted for each plant species and these are available for purchase. They come as a dry powder which is sprinkled over the seeds before planting.

When the seeds germinate the Rhizobia enter the plants root systems in a beneficial relationship. The bacteria capture nitrogen from the air in the soil and store it in a plant usable form in nodules on the plant's roots. The host plant can use some of the nitrogen directly and then when the plant dies and the roots rot in the soil that nitrogen then becomes available to other plants.

Other sources of nitrogen are composted manures, chicken and rabbit manure being highest in nitrogen. The manure also adds organic matter to the soil to help loosen up the clay and hold moisture. Manure also helps add the trace minerals zinc and sometimes has some iron in it. These two minerals are needed in smaller amounts than nitrogen but are very necessary for the plant to be able to use the nitrogen it has to make chlorophyll. A good website with color photos to help you understand what nutrient deficiencies look like is Plant Physiology Online Symptoms. Recycling all of your yard and kitchen waste as compost will help prevent deficiencies, although you may have to bring in some mineral fertilizers the first few years to build up a supply in the soil of those that are missing.

A good source of nitrogen and iron for the garden is blood meal. This is dehydrated blood from slaughterhouses. I always buy the organic brand just to be safe, as it is possible that Mad Cow Disease could be passed along through this type of material. (I don't think it very likely at this time here in the US, but better safe than sorry). Sometimes dogs and other animals may be attracted to the smell, while it is said to repel rabbits when sprinkled around plants they are eating.

Good root crops need potash. Looks like my soil still needs some!

Potash is the nutrient needed to make good roots. If you have not been able to grow good carrots, parsnip, potatoes, radishes and other root crops then this could be part of the reason. While horse manure contains the highest amount of potash of all the animal manures root crops should not be planted where you have used manure this year, it makes the roots forked and hairy. Wood ashes are a good source of potash but should NEVER be used on our soils. They are very alkaline. Our soil is already very alkaline and many plants already have a hard time growing here because of this. (In states where the soil is very acid wood ashes are a good replacement for lime to raise the pH as well as supply potash and some trace minerals)

Because I have not yet found any local nursery or garden center which carries a potash fertilizer I order mine from California in 50 pound bags. The fertilizer costs less than the shipping, but one bag will last me a couple of years depending on how much gardening I'm doing and how much new ground I'm working.

Phosphorous is the plant nutrient that makes for sturdy stems. A lack of phosphorous shows as stunted slow growing plants with weak stems. Some plants like corn and the cabbage family will turn purple on the bottom of their leaves when phosphorous is in short supply. In the Globe-Miami area you will probably not see a deficiency of phosphorous unless too much nitrogen and potash have been added to the soil, getting it out of balance or in plants growing in pots, especially in sterile potting soils that do not have a lot of plant food.

The only thing I add phosphorous to is long term container plants. Bone meal contains a high amount of phosphorous, again I only buy the organic brand to prevent any possibility of mad cow disease. You will read in many places that you should add some bone meal to your flower bulb plantings. Since bulbs are made up of layers of plant stems they do need phosphorous but our soils are already high in this mineral so it is superfluous to add it to our soils here. Bonemeal is also very attractive to dogs which will dig up the planting bed looking for the phantom bone!

What about Miracle Gro and other chemical fertilizers? I personally do not use them. The nitrogen they contain is obtained by a chemical process that burns up natural gas, causing a great deal of pollution. They do not contain any organic matter to improve the texture and water hold capacity of the soil. In fact, chemical fertilizers kill off much of the soil life, including earthworms, that make our soil alive and help our plants to grow.

The pH or acid/alkaline balance of the soil is very important. The pH scale goes from 0, very acid to 14, very alkaline, with 7 as the neutral point. Due to chemical reactions in the soil some minerals are 'locked up' in forms that plants cannot use when the soil is too far either way from neutral. The ideal pH for garden soil is about 6.5, at this level most plant nutrients are available in plant usable forms. The problem we have here is that our soils are very alkaline, this is why we so often see deficiencies of iron, zinc and some other trace minerals in our plants. These minerals may be present in the soil but they are not in forms that the plants can use.  The best remedy is to add lots of organic matter to the soil in the form of compost, leaf mold and manures. Organic matter forms mild acids in the soil which helps lower the pH and helps dissolve minerals into plant usable forms. When forming new garden beds the first year I also add a lot of peat moss to them. While the moss does not have much plant food in it, it is very acid and helps lower the pH of the soil. Peat moss can also hold a great deal of water. It will break down over time, but it is very helpful the first couple of years in the garden, especially if you do not have a lot of compost yet. I usually add about 4 cubic feet of peat moss to 100 square feet of garden bed.

Next time I will tell you about foliar fertilizers and how to use them. Please, if you have any questions, just ask! I am putting this information here to help you grow the best gardens possible and am trying to be of help. I have a lot of experience and am very happy to answer your questions.