What is nitrogen and why does our garden need it?

Nitrogen is a nutrient essential to a healthy lawn and garden. Plants that “fix” nitrogen, such as peas, beans, alfalfa and clover give a boost to poor garden soils. Many gardeners throw around the term “nitrogen fixer” but some do not know what this is how it is important to the soil. We are told to plant peas, beans and nitrogen fixing cover crops to enrich our soil, but how exactly does all of this work?

Plants fix nitrogen by drawing it out of the air and converting it to a form the plant can use. They do this through nodules on the roots. (You can see these nodules if you pull up a mature plant.) Rhizobia are bacteria in the soil that, once they are inside the nodules in legume roots, fix nitrogen. This process involves merging nitrate or ammonium ions. Sulfur, potassium and phosphorus all aid this process. Soils with less acid also help this process work better. Adding organic matter like grass clippings to the soil will enrich it, but won’t provide as much nitrogen as the organisms that break down the plant matter will need to use nitrogen for the process.

Beware of adding too much nitrogen to your soil and also adding them to the wrong plants for the wrong reasons. Too much fertilizer in the soil can lead to “burn” from a high concentration of mineral salts. If you want to encourage flowers, cut back on nitrogen or you will end up with leafy foliage instead of plentiful blooms. Also, fruit and vegetable plants may produce small or nonexistent crops. A high nitrogen fertilizer is best reserved for leafy plants like spinach, kale, lettuce and cabbage.

Avoid adding nitrogen fertilizers to your lawn before leaving on vacation or it will grow too wildly while you are away. In general, take care not to over-fertilize your lawn as the unneeded nitrogen can run off and get into the drinking water supply. Not only does this cause problems with over-fertilizing algae in the Chesapeake Bay, but nitrate in the drinking water can be dangerous to both pregnant women and infants. (It causes a form of blue-baby syndrome.)

To add nitrogen to the soil, try incorporating blood or bone meal. Fresh manure works well but should be added a few weeks before planting or it will be too harsh on young seedlings. Coffee grounds, fish emulsion, and grass clippings also add nitrogen. Dusting the soil with lime will help lower the acid content, if it is too harsh. If you plan to not use the garden bed for awhile, plant a nitrogen fixing cover crop. If planted in the fall, ground covers like winter rye, clover and hairy will also help keep your garden soil from blowing away in the winter winds. In the spring and summer, crops of peas, corn and beans will provide vegetables for you as well as enriching your garden soil.