Natural Sources of Nitrogen for Your Garden

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Jul 03, 2014 | Laura Firszt

Photo: OldGreySeaWolf/morgueFileRecently, the leaves of my beautiful geranium plants started to look a lot less beautiful. In fact they were downright yellow at the edges. With the dry spell we’ve been having, the “off” color definitely was not due to overwatering. When I searched the Net, it seemed the problem with my posies might be lack of nitrogen. This mineral is one of the most important nutrients for plants, necessary to their production of proteins, amino acids and DNA.

So I called the savviest gardening expert I know – my mother – for advice on how to naturally supplement my geraniums’ diet and give them the nitrogen they crave. Her immediate response: “Coffee grounds.”

Coffee Grounds

Mom was right. No-cost and readily available, coffee grounds are an excellent way to add nitrogen to your garden. In the process of decomposition, the leaftovers from your morning cup of java give off nitrogen, together with phosphorus and potassium. Mix the grounds gently into your soil, or add them to the compost pile. In the latter case, make sure that they are fairly dry so they don’t interfere with the aerobic quality of your heap. Although coffee beans are naturally acidic, the brewing process neutralizes their acid content to an insignificant figure.

Higher-Nitrogen Compost

Speaking of composting, it’s a great way to reduce landfills and replenish the earth. However, the typical mix of compostable materials may not contain enough nitrogen for nitrogen-loving crops like tomatoes, spinach, cabbage, corn and potatoes. High protein substances and fresh greens are best for boosting the nitrogen level of compost. Some examples are:

  • alfalfa
  • meal ground from cottonseed or soy 
  • composted manure or chicken droppings
  • fresh lawn clippings (free of herbicide or pesticide)
  • fresh fruit and vegetable scraps.

Seaweed is also a good source, though you'll have to wait about 15 weeks for its cellulose content to break down enough to release nitrogen. Please note that your municipality may have regulations concerning what types of materials are permitted in your compost heap. This is not an arbitrary restriction, but designed for effective pest control in Houston and other large cities.

Garden Management

Another way to enrich your soil with nitrogen is by careful  management. Rotate your crops, following a high-nitrogen-consuming veggie or flower with one that needs much less of this mineral. Or plant legumes, such as peas, beans, alfalfa or clover. These leguminous cover crops, sown early in the spring or in autumn, are excellent for the purpose of nitrogen fixation – depositing nitrogen absorbed from the air into their root nodules. Just cut legumes down before they flower and become woody; then dig the plants under to work that nitrogen into the earth. This process helps to loosen and aerate the soil as well.

Add Nitrogen with Caution

Overenthusiastic application of nitrogen can be counterproductive. It may stimulate plants like tomatoes to grow disproportionately (resulting in strong, healthy stalks but stunted fruit) and might even burn them, especially if it comes into contact with their leaves. Excessive amounts of nitrogen might seep or run off into nearby water systems, causing accelerated growth of algae. These algae produce toxins and bacteria that make the affected water dangerous for drinking. In addition, they decrease or eliminate oxygen in the water, with illness and death for the fish population as the consequence.

Test your soil before enriching it with nitrogen, and apply the mineral in small quantities. Use mulch to reduce run-off. For expert advice, consult an expert local landscaper.

Laura Firszt writes for

Updated January 3, 2018.

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