IN THE GARDEN NOW April 2018 HELPING GARDENERS PUT KNOWLEDGE TO WORK Understanding Soil Fertility in the Vegetable Garden Lisa Rayburn Extension Agent, Horticulture Contact Us: NCCE-Onslow County 4024 Richlands Hwy. Jacksonville, NC 28540 (910) 455-5873 (910) 455-0977 Fax http://onslow.ces.ncsu. edu North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating. Photo credit: Lisa Rayburn Understanding soil fertility and how fertilizers work is key to growing a vegetable garden. Sometimes discussions of soil and plant fertility get a little overwhelming for the beginning gardener so I am going to spend my newsletter space this month and next month discussing these topics. This month, I ll address our native soils and how they interact with three of the plant nutrients needed in the highest levels. Next month, I ll cover fertilizer formulations, how they behave in the soil and how that determines how and when you apply them. I m going to discuss this from the perspective of the vegetable garden, but the same concept applies to your lawn or flowering plants as well. If vegetable plants don t have enough nutrients, they won t grow or produce to their full potential and maybe more susceptible to insect and disease problems. Over fertilizing can cause problems as well excess vegetative growth and foliar disease, lack of blooms, problems with nutrient uptake, excessive salts in the soil and water quality issues downstream. Luckily, figuring out how to fertilize your vegetable garden doesn t have to be hard if you understand our soils on the coastal plain, the nutrients that plants need, and how these nutrients behave in the soil.
Many soils in Onslow County tend to be sandy and sandy soils don t hold on to nutrients very well. Soils that have higher amounts of silt and clay or organic matter will hold nutrients better. If your site was not used for farm land in the past, the chances are good that your soil is naturally low in many plant nutrients. If your site has been used for farmland, pasture, received applications of animal manures, or been in garden production for a while, then its nutrient profile will look different. Nitrogen, phosphorus and potassium are three nutrients needed by plants in the largest amounts. In fact, the three numbers on a bag of fertilizer stand for the percentage by weight of nitrogen, phosphorus and potassium. So a bag of 10-10-10 is 10% nitrogen, 10% phosphorus and 10% potassium. A forty-pound bag of this fertilizer would contain 4 pounds of actual nitrogen in the bag. Nitrogen, phosphorus and potassium behave differently in the soil. Nitrogen can move out of the soil rapidly in a variety of different ways taken up by plants, volatilized to the air, leached into the subsoil, utilized by soil microorganisms or bound up by soil particles. Phosphorus moves much more slowly in the soil, it tends to attach itself to soil particles and hold on tight. Potassium leaches out of sandy soils more readily than phosphorus does but not as quickly as nitrogen does. Not only do these nutrients behave differently in the soil, but plants don t take these nutrients up at the same rate. Generally, plants take up nitrogen, phosphorus and potassium in a 3:1:2 ratio. That is, they take up 3 parts nitrogen for every 1 part phosphorus for every 2 parts potassium taken up. Now this does not hold true for all plants or all parts of the plant life cycle but it is a general rate at which nutrients are taken up. Given the fact that many gardeners use a balanced fertilizer such as 12-12-12, it is common for the amount of phosphorus to build up in the soil over time. It s been applied at a high rate compared to plant uptake and it doesn t move out of the soil quickly. Excess phosphorus levels can cause problems though inhibiting the uptake of micronutrients from the soil and causing water quality problems when soil erodes and winds up in nearby waterways. Potassium levels can build up as well but potassium does not tend to build up to the same extent that phosphorus does since plants take up potassium at a higher rate and it leaches out of sandy soil more quickly. Local soils that have been fertilized for a long period of time often have excessive amounts of phosphorus and close to adequate potassium levels. Soil sampling is the only way to know for sure what the nutrient status of your soil is. You can stop by the extension office or call us at 910.455.5873 for detailed soil sampling instructions. I recommend sampling annually on new garden sites. Once you have been gardening in that location for several years, sampling every two to three years is sufficient. Soil sampling will tell you what level of phosphorus and potassium you have in the soil. Soil sampling does not test actual nitrogen in the soil because it is found in a variety of different forms and is not very stable. Instead, your soil sample will provide a recommendation for nitrogen application based on the crop that you coded for on the sample.
If you were to look at soil samples on the same site over time, a general trend for our soils would be the use of a balanced fertilizer (one containing equal amounts of N-P-K) or even one with a higher phosphorus and potassium level (such as 5-10-10) initially when a site is first brought in to production. This would account for the initial low nutrient levels in the native soil. This would be followed later by a fertilizer that is higher in nitrogen and potassium (first and last numbers such as 15-0-14) with little or no phosphorus as phosphorus levels increase in the soil. Once phosphorus and potassium levels are in the high end of adequate, you could maintain the garden using nitrogen only fertilizers (just the first number 15-0-0 or 46-0-0) and periodic soil sampling to ensure that additional phosphorus and potassium are not needed. Now, every site is different, but this is a good general rule of thumb. In your particular garden, your soil sample results will tell you whether your soil has adequate phosphorus and potassium to support the plants that you want to grow. If the levels of these nutrients are already adequate, you will not need to add them as part of your fertilizer program. The soil sample report will also tell you what, if any, ph adjustments need to be made. Proper ph is important since ph influences the availability of many plant nutrients. If the ph is too high or too low for your intended crop, the plant may not be able to take up the nutrients even if they are at adequate levels in the soil. Next month, I ll talk about the different types of fertilizer formulations, how they behave in the soil and how that influences application and plant growth. Onslow County Farmers Market Onslow County Farmers Market Opens for the 2018 Season - April 14th!!! The Onslow County Market will open for the season on April 14. We will celebrate with our Spring Fling on April 21. Join us for a selection of local produce, meats, wines, jams and jellies, honey, eggs, baked goods, crafts, vegetable transplants and more! Vendors vary from market to market so make sure you check out all three locations: Saturdays from 8:30 to 1:30 at 4024 Richlands Highway Tuesdays from 8:30 to 1:30 at 4024 Richlands Highway Thursday from 10 to 2 on Camp Lejeune (specific location to be announced) Please note that some market days and locations have changed from last year.
Tips and Tasks On the Lawn Our spring continues to be a rollercoaster ride. The early green up, encouraged by our warm February temperatures, has been followed by cooler March temperatures and frost which have browned many warm season lawns. These lawns will come back but this is an additional stress on the grass. Avoid applying herbicides and fertilizers to these lawns until after the lawns are actively growing and the grass has been mown several times. Post-emergent herbicides can damage lawns under stress. If you have portions of the lawn that were damaged by winter kill or large patch, pre-emergent herbicides will prevent you from being able to reseed those areas for several months. Your best option for now is to mow to keep the winter annual weeds under control and commit to treating them in November and February next year. Wait until May (zoysia, bermuda, St. Augustine) or even early June (centipede) before fertilizing warm season grasses. Bring samples by the extension office or email good photos to lisa_rayburn@ncsu.edu if you need help identifying your weeds and developing a control strategy. In the Vegetable Garden You can start seeding warm season crops like sweet corn, beans and peas in early April. Mid- to late- April is a good time to start setting out warm season transplants like tomatoes and peppers. Use your soil sample report to determine your fertilizer needs. If you are using a granular fertilizer, incorporate the recommended fertilizer into the soil and till in prior to planting your crops. Alternatively, till ¾ of the fertilizer into the soil and use the other half to band alongside your rows. Some crops will need an additional side dressing of a nitrogen fertilizer during the growing season. Tomatoes, potatoes, sweet corn, cabbage, squash, okra, beans and peppers will require a side dressing of additional nitrogen during the growing season. In soils with low phosphorus and potassium levels, you could use 3-4 cups 8-8-8 per 100 foot of row. If your soil has adequate phosphorus and potassium levels (or you have been gardening and using fertilizers in this area for several years), use two cups of calcium nitrate (15-0-0) per 100 foot of row. Slow release fertilizers are a great option for raised beds, containers and sandy soils. If using a slow release formulation, apply at the labeled rate and work in to the soil at planting time. The special polymers surrounding the fertilizer will ensure that the nutrients are released slowly through the growing season. In the Flower Garden You still have time to transplant and divide perennial plants before the heat of summer sets in. Choose a cool, cloudy day to reduce stress on your transplants and watch them closely through the summer to ensure they have adequate moisture to get established. Remember to top of your mulch if it is getting a little thin but you don t need more than 3-4 inches of good organic mulch in a bed. Too much mulch can inhibit the movement of water and nutrients down into the soil. If you use a weed preventer such as trifluralin (the active ingredient in Preen Garden Weed Preventer), make sure you remove any established weeds prior to application. These weed preventers work by inhibiting the germination of tiny weed seeds, so ensure an even application and try not to disturb the surface of the soil after you have applied the herbicide according to label directions.
Association Meetings Onslow County Master Gardener Volunteer Association Meeting April 12, 9 am Contact: Lisa Rayburn, 910.455.5873, http://lisa_rayburn@ncsu.edu Onslow County Beekeepers Association Meeting April10, 7 pm Contact: David Peed, 910.330.7584 or myscubashop@yahoo.com Classes Vegetable Gardening 101 Series 10 am Cost: free Registration: 910.455.5873 Location: Discovery Gardens We will meet the third Saturday of each month, at 10 am, in the Discovery Garden (besides the Farmers Market). Come plant and tend the vegetables in the raised bed gardens with us. Each month, we will discuss what we are planting and why. Then you can help plant! These informal classes will be a great way to get your hands dirty, ask questions and get ideas that you can apply in your own garden. Back to Basics Gardening Series Wednesdays, 6-8 pm Cost: free Registration: 910.455.5873 Location: Onslow County Extension Office April 4 - Common Vegetable Garden Problems April 11 - Getting Started with Backyard Chickens April 18 - Growing Fruit in Onslow County April 25 - Composting Pruning Trees and Shrubs April 14, 9 am - noon Cost: free Registration: 910.455.5873 Location: Onslow County Extension Office Barbara Fair, extension specialist, will discuss proper pruning of trees and shrubs. Weather permitting, we will go outside and practice pruning hands on.
Spring Garden Symposium April 21, 8:30 1:30, Discovery Gardens (beside the Farmers Market) The Master Gardener Volunteers will have tomato and pepper transplants for sale as well as a garden yard sale including items like birdhouses, sand castings and trellises. Shelton s Herb Farm and Ash s Japanese Maples will be on site with their plants as well. Event located in Discovery Gardens. Classes will run through the morning including: Vegetable Gardening 101, 10 am - Rich Mullins, Master Gardener Growing Herbs, 11 am - Shelton Herb Farm Growing Japanese Maples, 12 pm Ash s Japanese Maples Online Plant Sale The Master Gardener Volunteers will be partnering with Gardens Direct to offer an Online Plant Sale. You will browse the availability online, place your order online, and a local nursery will deliver gorgeous plants to us for you to pick up on April 21. Orders will be taken online between Friday, April 13 th and Thursday, April 19 th. Contact us at 910.455.5873 or email lisa_rayburn@ncsu.edu if you are interested in this event. Backyard Wildlife Class for Adults April 28th from 10 am until 1 pm Join the NC Wildlife Resources Commission and Onslow County Master Gardener Volunteers in a fun and educational workshop on backyard wildlife. Participants will learn about the biology, behavior, and habitat needs of common wildlife that may frequent their yards, as well as gardening and landscaping tips to provide a safe haven for wildlife. Cost is free, contact Emilee Morrison at NC Cooperative Extension to register at 910-455-5873, or emroz@ncsu.edu. Location: Onslow County Extension 4024 Richlands Hwy. Jacksonville, NC 28540. Participants are eligible for Criteria II credits of NC OEE Environmental Education Certification and school teachers receive CEU credit. Backyard Wildlife Class for Families May 5th from 10 am until 12 pm Join the NC Wildlife Resources Commission and NC Cooperative Extension for a fun, hands-on workshop for children and families in Onslow County to learn about backyard wildlife. Participants will learn about different animals that may live near or visit their backyards, including the basic habitat needs and behaviors of the animals. Participants will also learn simple ways to make their backyards friendlier for wildlife, while enhancing the natural beauty of the landscape and exploring the outdoors. Cost is free, contact Emilee Morrison at NC Cooperative Extension to register at 910-455-5873, or emroz@ncsu.edu Location: Onslow County Extension 4024 Richlands Hwy. Jacksonville, NC 28540. Participants are eligible for Criteria II credits of NC OEE Environmental Education Certification and school teachers receive CEU credit. CONTACT US If you have questions about lawn, landscape or garden problems, contact your local Cooperative Extension office. In Onslow County call 910.455.5873, Mon. Fri., 8 am 5 pm, or visit us online anytime at http://onslow.ces.ncsu.edu. While you are there, you can post your questions to be answered by email using the Ask an Expert widget in the upper left-hand corner.