Demystifying Nitrogen

Demystifying Nitrogen

Fertilization is a subject that throws many a gardener for a loop. It can be confusing, and we in the professional horticulture world understand. This topic will almost always be approached from the prospective of nitrogen. So why does nitrogen get so much attention? What is its role in plant growth? Nitrogen is the primary driver of protein synthesis, plant metabolism, energy creation, and is the structural component in chlorophyll. These are all extremely important functions leaving little doubt as to why it’s so critical. Your plants use this resource abundantly for healthy growth. The reason it gets so much attention is owing to its frangibility in the soil. Nitrogen goes through changes once applied to soils and is readily lost to the environment. For this reason, nitrogen application needs to be timed appropriately, and your cultural practices need to be such that encourage plant uptake over losses to the environment. Fear not my friends, this article will bolster your insight into the wonderful world of nitrogen, and have your plants growing strong and healthy.

The What and Why of Nitrogen

Nitrogen is one of three macronutrients identified in every fertilizer bag as the first of three numbers. This standardized NPK labeling refers to the amount of this nutrient in the bag by percentage of total weight. Application rates should be based on this number, and how much nitrogen you’ll need to cover a specified area. which number you use is based on the equipment you have to apply more so than the plant requirements.

Fertilizer bag
UF/IFAS Photo: Dan Culbert

Nitrogen can be natural or man made. Natural sources come in the form of composts, manures, and through atmospheric deposition. The later of these sources means rain, which washes nitrogen out of the atmosphere and into your soils. Man made sources conversely come in bags and are the result of a combustion process developed by Fritz Haber, and Carl Bosch circa 1910. Either way, nitrogen will be in the form of ammonia, nitrate, ammonium, or urea. Knowing this is important as it will dictate application methodologies. For instance, urea applied to the surface will escape into the atmosphere if not incorporated into your garden.

Fertilizer label showing types of nitrogen used.
UF/IFAS photo: T.W. Shaddox

Nitrogen type will also affect soil pH. This is especially important with ammonia-based fertilizers as residual acidity from them may lower pH. Applying the correct type will mitigate large unwanted changes in soil. Why are we concerned with soil pH? It speaks to nutrient availability and, thus how well your plants grow.  It can be overwhelming, but with soil testing and a call to your extension office, it’s easy to identify the appropriate fertilizers for your application.

Reactions in Soils

Soil is often considered inert, holding plants in place while providing a pantry full of the nutrients they crave. Nothing is further from the truth. Soil is a living entity with its own physical and chemical properties. The addition of anything, including irrigation, affects these properties.

Nitrogen takes two forms in your soil aside from nitrogen source. Inorganic nitrogen is converted from soil organic matter in a process known as mineralization or added from bagged fertilizers and is available for plant uptake. Organic nitrogen is unavailable for plant uptake and will be present in the natural forms listed in the previous section. Both are susceptible to the nitrogen cycle and may be lost to the environment. This happens as water passes through soil (leaching), erosion, runoff, or is lost to the atmosphere through volatilization and may have negative effects on surrounding water bodies.

Nitrogen cycle illustration
UF/IFAS Photo

To mitigate these risks through responsible fertilizer application, irrigation management, and landscape design. Apply fertilizers when plant uptake is favorable, and only to the level required by your plants. This will be during heavy vegetative growth periods such as initial installation. Irrigate as dictated by your plant life vs on a timer. Watering is a vital practice, but often overdone. Keep water levels enough to avoid plant stress but not excessive. Doing so reduces leaching potential and will keep your plants healthier. Finally, design your landscape with Florida Friendly Landscaping principles. Integrate diverse plant life, including turfgrasses and landscaped beds. The goal here is to allow enough plant life to absorb excess storm water, and support local pollinator populations.

Nitrogen is a critical piece of your fertilizer routine. It’s important to understand how it reacts with both your plants and your soils. A little knowledge can go a long way to keeping your plants healthy while mitigating risks from over fertilization. For more information, see this Ask IFAS document, or contact your local extension agent for additional information on this and any topic regarding your gardens and more.

Weak Lawns Respond to Warmer Soil & Correct Care

Weak Lawns Respond to Warmer Soil & Correct Care

Now that we are moving into warmer soil temperatures, weak areas in lawns will have a better chance of making some recovery. However, this is highly dependent on whether or not correct lawn maintenance practices are followed. These practices include fertilizing, mowing and watering correctly.

Many North Florida lawns came out of winter weak and thinning this spring. In areas of the lawn where there is at least sixty percent cover of the desirable type of lawn grass, recovery is possible. But where there is less than sixty percent desirable cover, reestablishment should be considered.

Applying the correct type and amount of fertilizer will promote lawn recovery. To maintain a healthy Florida lawn, it’s critical to use a fertilizer with adequate potassium. In most cases, use a lawn fertilizer with equal amounts of nitrogen (first number) and potassium (third number) such as 8-0-8, 10-0-10, 15-2-15 or similar analysis. Phosphorus (second number) should be low or zero unless you have the results of a reliable soil test indicating that more phosphorus is needed. Err on the side of being light handed when applying fertilizer to the lawn. In North Florida, most lawns will do just fine with an application in spring no earlier than mid-April and a second application in summer no later than mid-September.

Follow these mowing practices for a healthy lawn.

  • Never remove more than 1/3 of the leaf blade height at any one time.
  • Here’s the recommended mowing height in inches for each lawn grass: bahia – 3 to 4; centipede – 1.5 to 2; standard St. Augustine cultivars – 3 to 4; dwarf St. Augustine cultivars (Captiva and Seville) – 2 to 3; zoysia cultivars suitable for home lawns- 2 to 2.5; bermuda – .5 to 1.5.
  • Keep mower blades sharp.

Follow these irrigation practices for a deeper rooted and drought tolerant lawn.

  • Turn your automatic sprinkler system off and learn to operate it manually on an as-needed basis. Your lawn needs water when leaf blades start to fold in half lengthwise or when footprints remain visible in the lawn long after being made. Irrigate when at least 30% of the lawn shows these signs of water need.
  • Apply ½ – ¾ inch of water when you do irrigate. Place empty, straight-sided cans in the area being irrigated to see how long it takes to reach this amount.
  • Irrigate during early morning for more efficient water use and to minimize lawn diseases.

Here is a link to a UF/IFAS Extension publication on Best Management Practices for a Florida lawn. http://edis.ifas.ufl.edu/ep236

Math for the Home Gardener

Math for the Home Gardener

Math isn’t always fun! Here is Euclid explaining math in Raphael’s The School of Athens. Credit: Creative Commons.

There are a lot of things gardeners need to know to cultivate a beautiful landscape. Between plant zones, scientific names, soil chemistry, and pest identification, being a gardener takes curiosity and willingness to learn new things. Unfortunately, one topic that needs to be well understood, especially when it comes to applying pesticides and fertilizers, is a subject that many cringe when they hear it – mathematics!

Some of the most common mathematical concepts to have a good grasp on for gardening include area, converting decimals to percentages and vice versa, estimating volume and converting units, and determining how much fertilizer to be applied based on your fertilizer grade.

Here’s a couple tips to help you gardeners out with math.

Area

Most often, we need to know the square footage of our gardens. Rectangles are straightforward, you multiply length (in feet) by width (in feet) to get feet squared. Since most yards are not rectangles, we sometimes need to use other shapes to best calculate the area, such as circles and/or triangles. The area (A) of a circle is , where “π” is 3.14 and “r” is the radius (half of the diameter or the distance from the center to the edge). Remember that the little raised 2 means you multiply the radius by itself twice, not by two.

Most of the time, square feet is the best area unit to use. But just in case you need to know, one acre equals 43,560 square feet. So, if you find your lawn is 10,000 square feet, that means you have 0.23 of an acre (10,000/43,560).

Get your calculator’s out! Credit: iStockphoto.

Percent Conversions

This one may be better understood by most, but this becomes important later when we determine fertilizer needed or doing volume conversions. Basically, any percent can be divided by 100 to convert it to a decimal that can be used easily in other calculations. For example, 15% is the same as 0.15 (15/100). The easy way to remember is that 100% is the same as one, and 50% is the same as 0.5.

Volume Estimation and Conversions

Determining volume is required when figuring out how much mulch is needed for a garden bed or soil required for a raised bed. Converting one unit to another is especially important when determining how much pesticide product is needed to prepare a mixture.

For mulch and soil, the cubic feet (cf) or cubic yards (cy) are needed to figure out how many bags or truckloads will be needed. Most bulk products are sold by the cubic yard. Since we are dealing with volume, we need three measurements, the length, width, and depth. If we want to add three inches of mulch to a 500 square foot garden, we multiply the 500 by 0.25 feet (3”/12” equals 0.25 inches) to get 125 cubic feet. That is about 62 bags of mulch from the hardware store, which are often sold in 2 cubic foot bags. If we divide 125 cubic feet by 27 (three feet in a yard so 3’ x 3’ x 3’ = 27) we now have the answer in cubic yards and find that we need about 4.5 cubic yards of mulch. One cubic yard is roughly a half of a full-size pickup truck bed.

When it comes to converting liquid volume units to help with pesticide mixtures, fortunately we have the internet to help. However, it is a good idea to at least be familiar with converting ounces to gallons and vice versa. Since 128 ounces equals 1 gallon, to go from gallons to ounces you multiply by 128. For example, 0.5 gallons equals 64 ounces (0.5 x 128). To go from ounces to gallons, we just divide by 128. For example, 192 ounces equals 1.5 gallons (192/128).

Applying the proper amount of fertilizer keeps your landscape healthier and protects local waterbodies. Credit: UF/IFAS.

Calculating Fertilizer Needed

Okay, bear with me, as we are about to do some hard math and piece together several of the above concepts. First of all, most fertilizer rates are provided by extension resources and given in terms of pounds of a particular nutrient for a set area, usually 1,000 square feet. For example, when using slow-release fertilizer a homeowner should apply no more than one pound of nitrogen for every 1,000 square feet of lawn. To figure out how much actual fertilizer to apply to meet the recommendation, we will need 1) the recommended rate, 2) the size of the lawn, and 3) the fertilizer grade on the product (the three numbers that represent the percent N, P, and K). Our rate is one pound nitrogen per 1,000 square feet. The size of our lawn is 50 feet by 30 feet, so 1,500 square feet. We are going to use a 16-0-8 fertilizer. Now, here is the hard part! To figure out how much of our 16% nitrogen fertilizer will provide one pound of nitrogen, we need to convert 16% to a decimal (16/100 = 0.16) and then divide the amount of fertilizer we need by that number – 1 pound/0.16 – to find that 6.25 pounds of our fertilizer product are required for each 1,000 square feet. Since we have 1,500 square feet, we need to multiply our answer by 1.5, which gives us a total of 9.4 pounds.

Math is hard and there are usually many methods to get the same solution. When using pesticides and fertilizers in the home landscape, it’s important to make sure we’re using the right amount of materials to minimize the chance of harming ourself, our plants, and the local environment. If you need help, or would like someone to check your work, contact your local extension office.

Summer Tasks

Summer Tasks

Summer should be the time to relax and enjoy the fruit of all the hard work performed in the landscape over the previous winter and spring.  However, there are still some essential tasks that need to be completed during the summer.  Perform them in short energy bursts early in the morning or late in the evening.

1. Aerate Your Lawn

If your yard is starting to look weak and thin, even with fertilizing and proper moisture, it may need aeration.  Aeration, which is creating channels into your lawn, allows water and nutrients to reach the deep roots of your grass more efficiently.

To test if you need to aerate your lawn, shovel up a patch of grass to a depth of at least four inches.  If the layer of thatch is a half-inch thick or higher, your yard would benefit from aeration.  There are self-drive aeration machines and tractor-pulled devices you can rent to make quick work of large areas.  For smaller areas, simply punching multiple holes with a pitchfork will do the job.

2. Fertilize

Gardener fertilizing yard
Commercial landscape fertilizer applicators must obtain state certification.

Turf grass often displays a yellow color during the mid-summer rainy seasons due to the heavy rains flushing nitrogen away from plant roots. If your lawn is looking sad and yellow, chelated iron can often give a temporary green-up. Iron is not a replacement for nitrogen, but it can work well during our summer rainy season.

If you soil test revealed a potassium or magnesium deficiency, summer is a good time to make the last corrective application.  Potassium (K) is an essential macronutrient. Fertilizer bags typically show the percentage of potassium in a product as the third number displayed on the front of the bag (e.g., the “8” in 16-2-8). Potassium acts as a “vitamin” for turf grass, increasing root strength, disease resistance and cold hardiness.

Magnesium (Mg), also a macronutrient, is essential for the production of chlorophyll, necessary for photosynthesis, and also plays a part in the movement of carbohydrates from leaves to other parts of the plant.

3. Don’t Mow Too Short

It’s a natural inclination to want to mow your grass as short as you can, so you have the longest time until you have to mow it again. However, giving your grass a buzz cut every time you mow can hurt your lawn over time.

While some turf grasses can be mowed relatively short, like Bermudas and some Zoysias, most grass types shouldn’t be cut shorter than two-and-one-half to four inches high.  Mowing shorter than that can damage the growth point and leave it susceptible to disease and pest infestation.  It can also dehydrate the grass and lead to long term damage.

5. Water Infrequently but Deeply

One common mistake made by many is watering too often and too shallow.  When only given frequent shallow waterings, grass will begin to grow their roots upwards to take advantage of the small amounts of water, which makes weak and unhealthy.  The grass becomes even more dependent on water and very susceptible to disease and insect attack.

Try watering only once or twice a week, but for a considerably longer time so that the water can penetrate deeper into the soil and encourage downward roots.  Ideally, each irrigation zone is calibrated to determine the length of time it take to deliver ½ – ¾ inch.  Then set the system to run every 3-4 days for that number of minutes.  While checking the irrigation delivery system, make sure the rain shut-off device is working and set to the same ½ – ¾ inch.

6. Prevent Mosquitoes

Summer rains on a nearly daily basis lead to lots of standing water. In less than one inch of water, hundreds of mosquitoes can hatch 3 -5 days later. Not only are these blood-sucking pests annoying, but they can also transmit dangerous diseases like West Nile and Zika Virus.  Even without disease, their bites are painful and irritating.

To prevent mosquitoes, make sure no standing water is allowed to remain in your yard, either in low points or in empty containers like flower pots or wheelbarrows.  Any amount of stagnant water is the perfect breeding ground for mosquitoes.  Take a walk around the yard, dumping out water and disturbing the oak and magnolia leaves that are acting a collection cup.  Treat birdbaths and water features with floating “donuts” specifically designed to kill mosquito eggs.

While getting tasks done in quick morning trips to the yard, make sure to keep hydrated.  Heat exhaustion can happen fast.

Using Clover as a Winter Garden Cover Crop

Using Clover as a Winter Garden Cover Crop

One of the major recent movements in production agriculture has been the widespread adoption of cover crops.  This practice gives farmers a host of benefits, from erosion prevention to nutrient retention and recycling.  However, using cover crops isn’t just for large scale farming operations.  Hobby vegetable gardeners can absolutely employ similar systems on a smaller scale to reap the same benefits.  For the past two years, I’ve used Buckwheat to provide a soil building cover during the heat of summer between spring and fall gardens.  This winter, after my fall greens garden succumbed to frost, I decided to employ the same tactic with a mix of Red Clover (Trifolium pratense), White Clover (Trifolium Repens), and Crimson Clover (Trifolium incarnatum) to enhance my soil during the coldest months until spring tomato planting arrives!

Clover mix used as a cool season cover crop in raised beds. Photo courtesy Daniel Leonard.

While there are many different species of plants (rye, oats, wheat, various brassicas, etc.) that can be planted in November or December as cool season covers to deliver benefits like winter weed suppression, enhance soil organic matter, retain and harvest leftover nutrients, and provide habitat for beneficial insects, I chose Clover for an additional reason.  In addition to the above benefits, Clover is a legume and also fixes atmospheric nitrogen, making it available for subsequent plantings!  Not only is Clover an excellent soil cover, but it also provides some nitrogen fertilizer to the following vegetable garden!

Growing Clover, while not quite as simple as Buckwheat or small grain covers like oats and rye, is relatively easy for most gardeners.  The first step is selecting which clover species and/or variety to grow.  I chose a mix of Crimson, White, and Red Clover simply because I had several pounds of each left over from a previous field planting.  However, any one of the three may be used by themselves or in various combinations.  All are excellent choices for garden cover crops and have similar growing requirements.  Crimson Clover is the most readily available, but all three species can be found at most farm and garden supply stores.

The next step is to prep your garden beds for clover seeding.  I thoroughly remove weeds from my raised beds, lightly till the top couple of inches of soil, and rake to provide a level surface.  Since clover seed is tiny, a smooth, clean seedbed is a must for excellent germination.  Once this is done, your next should determine how much seed to plant.  Recommended clover seeding rates are usually given on a per acre basis and range from 3-4 lbs/acre (White Clover) to 20-25 lbs/acre (Crimson Clover).  Given these seeding rates, planting in a 4’x8’ (32 ft2) raised bed is only going to require a miniscule amount of seed.

Clover mix used as a cool season cover crop in raised beds. Photo courtesy of Daniel Leonard.

To ensure a good stand while minimizing risk of overplanting, I mix equal parts clover seed and either sand, vermiculite, or other media similar in size to clover seed and hand scatter over the surface of my beds, making sure to uniformly cover the entire bed.  If you think the stand is too thick, you can always hand-thin after emergence.

As a group, clovers prefer moist soil that is not allowed to dry out completely.  This isn’t usually a problem given the Panhandle’s frequent rainy cold fronts in winter, but if rainfall is inconsistent, some irrigation will be required.  Supplemental fertilizer isn’t normally necessary when planting a clover cover in vegetable gardens because nutrients remaining from the previous veggie crops are usually sufficient for growth and development (N especially is not needed as legumes produce their own through N fixation).  2-3 weeks before you’re ready to plant your spring veggies, chop the clover cover into the top few inches of your bed to terminate it and release its nutrients back into the garden.  It’s that easy!

Planting a winter legume cover crop like clover is a great way to harness the benefits of cover crops for your spring veggies and enhance the aesthetics of your otherwise barren and drab garden beds!  For more information about growing winter cover crops or any other horticultural topic, contact your local UF/IFAS County Extension office.  Happy Gardening!