Spring Fertilization Guidelines for Home Gardens

As we enter the spring growing season, this is the perfect time to apply fertilizer, especially as your plants are leaving their winter dormancy. Applying fertilizer now allows the plants to make use of it as warmer temperatures trigger that first flush of growth. If you would like to fertilize your lawn, I recommend a first application later in April. Lawns also benefit from more specialized fertilizers that are lower in phosphorus.

What fertilizer you use depends on what you are growing and your landscape goals. For an area you are cultivating intensely, I strongly encourage you to do a soil test before making fertilizer choices. If it is an area you have previously fertilized, you may find that no additions are necessary or that a pH modification is necessary. Soil pH is one of the biggest factors that determine whether a plant can use nutrients in the soil. In some extreme cases a soil may have all the nutrients a plant needs, but the pH of the soil prevents plant uptake.

Most established landscapes will not require a heavy or specialized fertilization. You can use a general fertilizer like 8-8-8 or 13-13-13 with good success in those circumstances. For maintaining plant health without encouraging vigorous growth that will need to be pruned back, I recommend a light broadcast application of shrubs and trees. Again, the rate depends on plant material, age and location. When applying fertilizer, a light incorporation can be very beneficial as well if it does not disturb the root systems present. An area where you plan to plant annuals or have your vegetable garden will benefit from a heavier application. I also strongly recommend having a weed control plan in those sections because it is not only your desired plants that benefit from the extra resources. Once you have done a March application, I consider making another one every two to three months throughout the growing season.

Remember, your soil is just as unique as you are. It may be best to get a soil test done to find out what conditions you have that are distinctive to your yard and local growing conditions. With that information your local extension agent can help you make choices tailored to perfectly fit your yard.

Cordiali Saluti,
Michael Polozola II, PhD

Fertilizer applied to containers and landscape beds should be applied evenly over the area.
Photo credit: Dr. Kathryn Fontenot

Terminal Tummy Aches in the Landscape

About 20 years ago, when I was a young service forester in Virginia, I learned about a biological control for the gypsy moth that was defoliating oak trees — Bacillus thuringiensis (Bt). Homeowners can use Bt to kill the worms eating up your foliage. Bt causes bacterial diseases of insects and is a safe, organic active ingredient that causes a stomach poison to develop in the gut of caterpillars. Newer strains can affect certain larvae, such as mosquitoes and leaf beetles.

Bt acts by producing proteins, or a “toxic crystal,” that react with the cells of the gut lining of susceptible insects. These Bt proteins paralyze the digestive system, and the infected insect stops feeding within hours. Bt-affected insects generally die from starvation, which can take several days. Bt is safe to use around people, pets, wildlife and honeybees.

The main disadvantage is that Bt is susceptible to sunlight, and the residual lasts less than a week, so other applications may be needed. Products with Bt have short shelf life, and Bt will not treat aphids and grasshoppers. It is effective on those caterpillars that become moths. That said, correct identification of the troublesome insect pest should always take place before any control method is implemented.

A quick review of the Louisiana Insect Pest Management Guide published by the LSU AgCenter reveals the vegetables on which Bt control is tested and suggested: broccoli, cabbage, eggplant, lettuce, mustard, parsley, tomatoes, and turnips. Brand name products in which Bt is the active ingredient include: Biobit, Bactospeine, Dipel, Javelin, Ketch DF and Thuricide.

Keith Hawkins, Area Horticulture Agent, Central Region

Fertilizer incorrectly applied to container-grown plants. Photo credit: J Stevens

The 2020 Spring Louisiana Super Plants

The Louisiana Super Plant program is an educational campaign of the LSU AgCenter that identifies superior plant material for Louisiana landscapes. Louisiana Super Plants have undergone rigorous trials and at multiple AgCenter locations across the state of Louisiana, as well as being vetted and approved by the Louisiana green industry. As such, Louisiana Super Plants are university tested and industry approved. Each year the AgCenter introduces new plants in both the spring and the fall. This year we have two amazing series of plants to announce in the spring. Both of these inductees are amazing bedding plants that will last throughout the warm season across the entire state. They are grown in full sun and bring an outstanding burst of color to any Louisiana landscape.

The first inclusion into the Louisiana Super Plants program for spring 2020 is the Lucky Star pentas. Pentas are some of the best plants for attracting pollinators to a garden, and with their bright vivid colors, pentas attract people as well! The Louisiana Super Plants program has already included Butterfly pentas, and the more compact Lucky Star pentas performed so well in our trials that it was time to add another group. Across our trialing sites and through the years, these were continually top performers. In fact, Lucky Star Dark Red was one of the top winners of 2018 in the Hammond Research Station Ornamental Trials, and Lucky Star Lavender was one of the top performers in the 2019 Hammond Research Station Ornamental Trials.

Currently, there are six different colors in the Lucky Star series, including Lipstick, White Improved, Deep Pink, Lavender, Violet and our favorite, Dark Red. These are more compact than Butterfly pentas and still keep the nonstop color throughout the season.

FlameThrower coleus is the second series that will be announced in the Spring 2020 Louisiana Super Plants. FlameThrower coleus can be spotted by their uniquely shaped foliage and their bold, lasting colors. These medium-sized coleus are great for landscape plants and also do well in large containers. Flamethrower coleus joins Henna coleus as Louisiana Super Plants.

Just like with Lucky Star pentas, FlameThrower coleus performed so well across the trials that it warranted another coleus addition to the program. FlameThrower coleus thrive in full sun and do best in well drained soils. Like most coleus, FlameThrower are low maintenance landscape plants, but this series is extra special because it is one of the last to flower in the landscape. FlameThrower coleus are currently available in seven spicy varieties, including Salsa Roja, Serrano, Habanero, Chili Pepper, Chipotle, Spiced Curry and Salsa Verde.

Dr. Jeb Fields, Commercial and Ornamental Horticulture Specialist

Vegetable Gardening

Spring is my absolute favorite season for vegetable gardening — and I am probably not alone. Cucumbers, tomatoes, peppers and more all grow this time of year. So, let’s get started!

Before Planting:

A great garden starts with a clean garden. Pull weeds and remove any fall vegetables that have already been harvested or are harboring insects. Lightly till the soil. Then take a soil sample. The LSU AgCenter Soil and Plant Testing Lab will provide you with results of the micronutrients and macronutrients in your soil that are available to plants, the soil’s pH and organic matter content. Soil samples cost $15 and are money well spent, especially because home gardeners really only need to run samples every three or so years. Make sure the soil pH is between 5.5 and 7.0. Adding lime will increase soil pH, and adding sulfur will decrease soil pH. If you plan to incorporate manure or compost, do so before you take your soil sample. We definitely recommend adding either, but if you chose manures, make sure they are aged at least 6 months old or older. Add fertilizer — your choice of organic or conventional — as the soil test recommends.

Planting Time:

Many great veggies can be planted in the next few months. Here are a few LSU AgCenter favorites.

March

Directly plant snap beans, Swiss chard, radishes, lettuce, collards, mustards, turnips, cabbage, broccoli and sweet corn seeds. Remember, sweet corn is wind-pollinated, so for full ears to grow, the corn must have good nitrogen fertilization and also in stands planted three rows wide or wider. The length of the row does not matter as much as the width of the planting. You never know which way the wind will blow. Plant tomatoes, peppers and eggplant transplants mid-month in south Louisiana and later in the month for north Louisiana. Plant cantaloupes, squash, cucumbers and watermelons well after the danger of frost is over; this is usually after March 15 in south Louisiana and closer to April 1 in north Louisiana. The cucurbits can be planted from seedlings or directly seeded into the soil this month.

April

Plant snap bean and butter beans. Butter beans or lima beans require a little more heat to germinate and grow nicely, so April is a great month to get them growing. Radishes, collards, cucumbers, eggplants, cantaloupes, okra, Southern peas (field peas), peanuts, pumpkins, winter squash, summer squash, sweet corn, sweet potatoes (late April), tomatoes (transplants), peppers (transplants) and watermelons are also great to be planted this month. Like butter beans, okra really needs warm soil to germinate, so you may need to wait until the middle of the month or even later. If the soil is cold, the growth will be slow, and the plant will be more susceptible to insect and disease attacks. Well-fed well-watered plants planted at the right time can withstand a lot more insect and disease pressure, so patience is key for warm weather and excellent okra germination. Many gardeners also recommend soaking okra seeds for a few hours in water or scratching the surface of okra seeds with sandpaper just to help with uniform germination.

May

Most spring vegetables can be planted in May because the soil has warmed and danger of frost has passed. Plant sweet potatoes (transplants), okra, Southern peas, pumpkins, peanuts, sweet corn, watermelons, cucumbers, butter beans, squash, cantaloupes, collards and eggplants (transplants). Snap beans, butter beans, sweet corn, tomatoes and peppers (transplants) should be planted in the early days of May to prevent poor fruit set because of high temperatures. If you have not had a chance to plant tomatoes yet, you can still do so, but the LSU AgCenter recommends planting heat-set tomatoes at this time of year — especially if it is late in May. Heat-set varieties include, but are not limited to, Solar Set, Sun Gold, Phoenix and Florida 91. If the name sounds hot … it is probably heat-set. Heat-set simply means that when night temperatures are above 75 degrees Fahrenheit, pollination and fertilization will still occur.

After Planting:

Once your spring plants begin to flower, add just a little bit of extra nitrogen, such as bone meal, calcium nitrate, nitrate of soda and potassium nitrate, to the plants. Place this fertilizer about 6 inches from the main stem to prevent burning the plants. This little boost of nitrogen will help increase fruit set and increase plant vigor. How much? That really depends on which fertilizer you use. Follow rates on the label. Water your plants at the base. Plants drink from their roots and not so much from their leaves. Identify insects before you spray. Some insects are good and others are bad. There is no use in spraying the good ones and no use in spraying the bad ones with insecticides that will not work. There is not a one-size-kills-all insecticide, so make sure to talk to your local LSU AgCenter extension agent when identifying both insects and disease. Also, enjoy the garden. Yes, it’s work, but — wow — can it be pretty, too! Put a bench or little table by your garden to sit back and relax.

Dr. Kiki Fontenot, State Vegetable Extension Specialist

Checklist for Spring

1. Treat lingering winter broadleaf weeds with herbicides containing the active ingredients atrazine, 2,4-D and mecoprop, dicamba and carfentrazone. You can also try organic alternatives with such active ingredients as citrus oil, iron HEDTA, 7.8% pelargonic acid, or clove oil and citric acid. Organic herbicides often require two applications for best control. Follow label directions for any herbicides used. Controlling winter weeds is the best practice for a healthy spring lawn.
2. Begin your preventative rose spray program in early March. Alternate fungicides to control blackspot and powdery mildew. Treat in the early morning or late evening every week. Copper is a great organic alternative to other traditional fungicides.
3. After spring bulbs that reliably return each year have finished flowering, wait until the foliage turns yellow before cutting it off. Food is being manufactured and stored for next year’s blooms.
4. Mulch plants to reduce watering requirements, suppress weed growth and minimize soil temperature fluctuations. Excellent mulches are pine straw, chopped leaves and pine bark. Mulch should be applied 2 inches thick for effective weed suppression.
5. Pull out the lawn mowers. You can make your first cutting in March. Gather and compost clippings.
6. Fertilize your lawns if your soil tests indicate a nutrient deficiency. You can begin fertilizing after the threat of the last freeze has passed. Usually after March 15 in south Louisiana and after April 1 in north Louisiana.
7. Fertilize shrubs in the spring using a general-purpose fertilizer such as 8-8-8, 10-10-10 or 12-12-12. Carefully follow the label directions.
8. Plant warm-season bedding plants beginning in mid-March (south Louisiana) or mid-April (north Louisiana) and continuing through early May. The list is endless. Whether you choose annuals or perennials is a personal choice. Annuals typically live only one year if we get a rather cold winter. Perennials will come back year after year from their roots. Here is a short list of great options — celosia, coleus, cone flowers, gaillardia, hibiscus, impatiens, marigolds, pentas, ornamental peppers, vinca, black eyed-Susans, torenia, sedums and zinnias. Consult the AgCenter website at www.lsuagcenter.com for a complete list of Louisiana Super Plants.
9. Lace bugs on azaleas and aphids or whiteflies on gardenias are common in the spring. Treat with horticultural oils or sprays as needed as an organic option. Also examine camellias, sasanquas and hollies for scale insects on the lower foliage. Control with acephate imidacloprid or use organic alternatives such as horticultural oils sprays.
10. To revive your cool-season flower plantings, pinch off old flowers on bedding plants after their first flower cycle is completed this spring.
11. Roses may develop insect problems. Watch for aphids on tender new growth, thrips on flowers and cucumber beetles on foliage. Beetles are especially a problem if a vegetable garden is nearby.
12. Spring is a great time to plant flowering trees and shrubs that will bloom in summertime. Plant these shrubs and trees (depending on the variety you select) for great flowering all summer. Some great examples are crape myrtles, butterfly bush, oleander, plumbago, hibiscus, firebush, ever-blooming roses, Encore azaleas, Shoal creek vitex and magnolias.
13. If your crape myrtles have had problems with crape myrtle aphids and the unattractive, black sooty mold they cause, treat your trees now to prevent problems this summer. Apply a drench of imidacloprid insecticide to the base of the tree, and the tree will be protected from aphids all summer.

Dr. Heather Kirk-Ballard, Horticulture Specialist

Lawn Weed Control

Herbicides can be effective tools for reducing weeds in your yard, but the best way to manage weeds is to grow a thick, healthy lawn. Lawns that are managed properly are lush and healthy, with few weed problems.

Visit www.lsuagcenter.com and search for the keywords “lawn BMP” for more information on growing a beautiful lawn.

Pre-emergence herbicides — Weed preventer or pre-emergence herbicides can be helpful in preventing the emergence of several summer annual grasses and broadleaf weeds. Pre-emergence herbicides may be applied safely in late winter to early spring to all established southern lawns.

Most pre-emergence products for home lawns are granular and should be applied with drop or broadcast spreaders and “watered in” soon after application. These types of herbicides kill weeds as they germinate, so application timing is extremely important. You have to apply before the weeds, such as crabgrass, germinate. They will not kill any existing winter weeds.

Residents in the New Orleans area and southernmost areas of the state should apply pre-emergence herbicides in late January or early February (definitely before Valentine’s Day) and then follow up with another application in mid-April. From Alexandria to Baton Rouge, residents should apply around Feb. 10, with a follow-up application in late April. If you live in north Louisiana, try to get these herbicides applied in late February to early March, with a follow-up application by mid-May. Some pre-emergence herbicide trade names to look for are Scotts Halts, Barricade and Hi-Yield Crabgrass Preventer with Dimension. Consult product labels concerning rates and application techniques.

Post-emergence herbicides — Post-emergence herbicides are used to kill weeds that already have emerged in the lawn. Winter broadleaf weeds usually are prevalent in the late winter to early spring throughout the state. MSM Turf (metsulfuron) and Celsius (theincarbazone-methyl + dicamba + iodosulfuron) are two highly effective broadleaf-killing herbicides that have consistently performed well in LSU AgCenter evaluations on winter broadleaves. MSM is effective on wild onion, false garlic and blue-eyed grass, which is actually an iris, as well as most winter broadleaves. These are low-use-rate herbicides, especially MSM. Follow the product labels very carefully so that lawns and trees are not injured. Do not use Celsius on carpetgrass.

More widely available broadleaf weed killers include trimec-type herbicides formulated with the active ingredients 2,4-D; dicamba; and mecoprop. Some examples of trade names to look for with these active ingredients include Trimec Southern, Ortho Weed B Gon for Southern Lawns, and Ferti-lome Weed Free Zone. Product manufacturers will often recommend a follow-up spray two or three weeks after the first application. Broadleaf weed killers such as these are widely available and can be used on most southern grasses. Injury can occur, however, when using them on St. Augustinegrass and centipedegrass as the weather gets warmer in late spring.

Atrazine is a herbicide that is effective on winter broadleaves and also controls annual bluegrass, especially when applied before the annual bluegrass flowers. Most garden centers have a good supply of atrazine on their shelves. Most weed and feed products labeled for St. Augustinegrass and centipedegrass contain atrazine as their active ingredient. However, liquid atrazine sprayed on weeds in the yard has worked better in LSU AgCenter trials than atrazine weed and feed products impregnated on a fertilizer granule.

What about weed and feed products? Weed and feed herbicides can be used at the times recommended for the first fertilizer application of the year. Apply weed and feed in the New Orleans area from mid-to-late March. For north Louisiana, mid-April is the time. Just be aware that applying weed and feed too early (late February to early March) may encourage outbreaks of large patch disease.

Clean your sprayers thoroughly with an ammonia solution if the same sprayer is used for applying insecticides or fungicides on landscape plants. It is best to buy a sprayer specifically dedicated for weed killers, however, to avoid accidental injury to desirable plants. As always, be sure to read and follow product label recommendations before using any pesticide.

Fertilizing the lawn

Lawns vary in the amount of fertilizer required during the growing season. See the table below for information regarding the number and timings of fertilizer applications recommended for lawn species grown in Louisiana. Bermudagrass and St. Augustinegrass require the most fertilizer compared to other lawn grasses. Centipedegrass and zoysia only require one to two applications of fertilizer per year.

Which fertilizer should I use during the growing season?

A spring application of weed and feed could serve as your first fertilizer application. For future applications during the growing season, consider using 3:1:2 or 4:1:2 ratios of N-P-K as a guide for the analysis of fertilizers to choose for the lawn. For example, a fertilizer with an analysis of 21-7-14 is a fertilizer with a 3:1:2 ratio. You would be better off getting your soil tested. Soil tests would be most helpful to determine exactly what nutrients are needed to make your lawn beautiful. Contact your parish extension office concerning soil sampling your yard today.

Dr. Ron Strahan, Weed Scientist and Turfgrass Specialist

Exobasidium Leaf Gall

Leaf gall of camellias and azaleas is a fungal disease favored by extended periods of cool, wet weather during spring. This is primarily a leaf disease, but it occasionally may occur on stems, flowers and seed pods. There are mainly two species of the Exobasidium fungus that cause this disease: Exobasidium vaccinia on azaleas and E. camelliae on camellias.

Symptoms of leaf galls start appearing soon after the plants finish flowering. Leaves are distorted and become thickened with a fleshy or leather-like texture (Figures 1 and 2). Galls tend to be pale green, pink or white (Figure 3) in the beginning, but as they develop, they become white and powdery. The white powder material is the spores of the fungus, which readily disperse via air currents and by splashing water. As the galls get older, they shrivel up, dry out and turn brown and hard (Figure 4). Older galls fall to the ground, where they survive and may serve as a source of incoculum for the next spring susceptible growth.

Management of leaf galls is achieved primarily by adopting good cultural practices in the landscapes. Proper pruning and discarding of galled leaves are very important in reducing the spread of the disease. Cut galled leaves a couple of inches below the symptoms and, before discarding them, put them in resealable clear storage bags, such as a Ziploc-style bag.

Remove and destroy affected leaves with galls that have fallen on the ground. Improve air circulation by selective thinning of the canopy of established plantings to promote rapid drying of foliage. Also, maintain adequate spacing when establishing new plantings to avoid creating favorable conditions for disease development. Fungicides may help avoid infection when applied beginning at bud break. Repeated applications may be required every 10 days as long as the conducive weather conditions persist for disease development. For fungicide selection, please consult your local LSU AgCenter extension agent. For more information on leaf galls of azaleas and camellias, please contact Dr. Raj Singh at 225-578-4562 or rsingh@agcenter.lsu.edu.

Dr. Raj Singh, Plant Pathologist and Director of Plant Diagnostic Center