Maryland Turfgrass Council – Planning and Procedures for Spring Seeding: A Good Job Can’t Be Done on the Cheap

March 13, 2023 | Maryland Turfgrass Council | PODCAST

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MTC TURF NEWS: Peter H. Dernoeden, Ph.D., Professor Emeritus, University of Maryland

Spring seeding is fraught with problems, but winter is a good time to prepare. Some basics include: getting a soil test; selecting quality seed blends and mixtures; addressing seedbed weeds with an appropriate herbicide; ensuring irrigation for dry periods; using composts; and providing erosion control measures. While spring seedings are much more troublesome than those performed in the fall, planning is the key to success. Cost is always a major factor, but a good job can’t be done on the cheap.

Soil testing is a step that too many professionals ignore. For big jobs, it is a must and it’s fast and easy. Getting a handle on soil pH is an important first step since it will greatly influence nutrient availability for many years. The best time to address soil pH extremes (and thus nutrient availability) is just prior to establishment when there is bare/open soil. With open ground, you can apply much larger amounts of either pulverized limestone [use where pH is < 6.0] or elemental “flowers” sulfur [use if pH > 7.0] to more effectively address pH extremes. It also is the best time to address nutrient deficiencies (esp. phosphorus). If you wait until after establishment, it may take hundreds of pounds of lime per 1000 sq. ft. applied over a period of years to set things right. A good target number is pH ≈6.5 and a soil test will give you guidelines on amounts of lime needed. DO THIS FIRST and acquire enough lime according to a soil test and incorporate (e.g., apply and till) the lime prior to seeding.

New construction sites in particular need to be sampled properly since there normally are excavations, trees removed, top soil improperly stock-piled, fill introduced and then everything mixed, pushed around and graded. Soil pH can vary greatly, even in a small area if soil is drastically disturbed. For example, in my lawn, an area carved from a wooded lot, I found pH ranging from 4.1 (probably sub-soil moved to the surface) to 5.8 (probably top soil). A big mistake is that too many just grab a spade full of soil for testing. So take the time to get a proper sample from at least three separate areas (i.e., say front, middle and back). Use a simple soil probe and take a dozen or more random samples from a 3-4” depth in each of the three or more separate sites. Other important numbers are those pertaining to phosphorus (P) and potassium (K) levels as well as organic matter percentages. A starter fertilizer is invariably used at seeding and contains a combination of nitrogen (N), P and K. For most purposes, the starter is formulated in roughly a 5:2:1 ratio, but it can vary and the soil test will indicate a proper ratio. The important thing for a spring seeding is to choose a starter that has about 50% of its nitrogen (N) in a slow release form. Phosphorus is another key element that should be applied to bare soil at establishment.

The only way to boost organic matter levels in soils is to incorporate a recommended material prior to seeding. The problem is that nobody ever figured out how best to proceed. Indeed, the idea of incorporating topsoil (way too expensive) can be an act of futility. Potential problems with topsoil include the following: without testing how are you to know its pH, nutrient and organic matter content; whether it has a poor ratio of clays and fines; whether it contains heavy metals or salts; etc. Finally, topsoil is heavy and trucking expenses likely will greatly exceed the cost of the soil.

There was a landmark study conducted at the University of Maryland as it relates to organic matter manipulation in soils of established turf. A seven-year study showed that no matter how much organic fertilizer (Ringer, Sustane and Milorganite) was applied to the turf surface, they had zero impact on boosting organic matter, as well as microbial populations, below the thatch layer and in the root-zone.

Soil Conditioners: Most soil conditioners are composts and sphagnum peat moss. They are incorporated into poor soils to improve water and nutrient holding capacity. Composts are partially decomposed organic matter and include cow manure, paper mill byproducts, mushroom soils, sewage sludges (aka biosolids); and yard waste materials (composted leaves, clippings, twigs, chipped branches, etc.) and byproducts of arborists. The most common compost that contains high levels of humus, that I am aware of, is called LeafGro (produced by Maryland Environmental Services, in Montgomery County, MD). LeafGro is the product of very well decomposed grass clipping and yard leaves. It is very dark-almost black in color, has a pleasant earthy odor and contains high levels of humus (thoroughly decomposed organic matter via microbes). What makes high humus products better than peat moss, and probably other composted materials, is that these products have superior water holding capacity (225% by wt.) and nutrient hold capacity, and freedom of hydrophobic properties. LeafGro is far less expensive than most other soil conditioners (e.g., sphagnum peat, yard and forest composts and similar products).

Peat moss is a primitive plant that contains no vascular system and is comprised of primitive branches, tiny (one cell thick) leaves and root-like rhizoids. Peat can be used in turf as a soil conditioner because it provides improved nutrient and water holding capacities. Peat moss, however, is water repellant (i.e., hydrophobic) and needs to be mixed with a wetting agent. Most products also are mixed with Perlite. Perlite is included since it aides in water infiltration and thus improves aeration. One of the best-known peat moss products is MiracleGro, but there are a multitude of similar sphagnum peat moss products. Peat moss is expensive, compared to organic yard waste composts, and thus is used mostly in potting mixes.

General information on selection and use of composts can be found in: “Establishment of Lawns with Compost and Microclover in the Chesapeake Bay Watershed; found by Googling Maryland Turfgrass Council Publications. The publication covers soil modification with composts; noting that a proper material can improve soil structure, increase nutrient and water retention, and provide nutrients. Yard trimmings probably are the most commonly used composts in turf. Yard trimming composts should be dark-brown to black in color, loose and crumbly, and have an earthy odor (avoid products smelling like ammonia or sulfur). Composts should be free of large, whitish-gray undecomposed wood chips (small, degraded/rotted slivers will be present); have a carbon: nitrogen ratio of about 30:1; and a pH range of 6.0-7.5.

University of Maryland researchers (Dr. Tom Turner and Dave Funk) performed pioneer work in using LeafGro as a soil conditioner for turf. To improve soil before seeding/sodding, apply a compost (e.g., LeafGro) to the soil surface with a 1 inch layer (3 cubic yards/1000 sq ft) or 2 inch layer (6 cu.yrds. /sq. ft.). The compost needs to be incorporated via rototilling into the upper 4 to 6 in. of soil, which is easier said than done. Using more than a 2” topical layer is extremely difficult to properly mix into the upper 4-6” soil. Excessively wet composts and/or soils cannot be thoroughly mixed. It is important that the compost be thoroughly mixed and not allowed to form clumps and layers.

Seed Selection: For most situations, including lawns, roughs, sod production, sports fields and other professionally managed areas, a blend  2 or 3 cultivars of tall fescue mixed with about 3 to 5% Kentucky bluegrass is best. Regionally adapted turf cultivars for mixes can be obtained from any County Extension office. In DE and MD, use University of Maryland’s TT77 “Recommended Turfgrass Cultivars for Certified Sod Production and Seed Mixtures in Maryland (Google Maryland Turfgrass Council Publications). 

Spring Seeding and Herbicides: There are too many scenarios to address here as it relates to seedbed preparation. Tilling, leveling, incorporating a recommended organic product (especially helpful in sandy as well as clay sub-soils) and firming are the basics. Assuming a uniform grade, killing existing vegetation and disk/drill seed also works well. After the seedbed has been prepared, it is very important to apply a seedbed-safe preemergence herbicide like Tenacity (mesotrione) or Tupersan (siduron). The reason being is that the most common cause for spring seeding failures comes from weed competition. While Tupersan is highly effective on crabgrass and foxtails, it has little or no impact on broadleaf weeds and sedges. Tenacity has been a major game changer in successful spring seeding’s because it safely targets a multitude of common broadleaf and sedge weeds as well as crabgrass. For best results, apply Tenacity at or just after seeding and then apply a second time four to six weeks later. Use a high label Tenacity rate (e.g., 6 oz. product/acre) if seeding into Round-up-killed vegetation. It works wonders in reducing weed competition, thus allowing seedlings to tiller and for stands to mature more rapidly. Note: Tenacity is highly toxic to bentgrasses. When seeding bentgrass, use Tupersan in the seedbed for safe and effective pre-emergence control of crabgrass and foxtails (not likely to control goosegrass or broadleaf weeds). Tenacity use will easily pay for itself; factoring in labor, time and costs to purchase and apply different herbicides targeting broadleaf and annual grass weeds. Tenacity is safe to use on cool-season grass seedlings (except bentgrass), but can bleach-discolor and/or thin seedlings if excessive rates are applied (e.g., in overlaps, etc.).

Irrigation can be a wild card. If available, it will greatly enhance success. In our region, irrigation generally is not needed in the spring until seedlings emerge. Seedling emergence is governed mostly by soil temperature in spring and timely rains that keep the seedbed moist. In general, it is best to wait until mid-April to seed to ensure soil temperatures are warm enough to promote turfgrass seed germination. Irrigation should be withheld as long as soils are moist, which again is likely to be the case in most springs. What you need to worry about most is the potential of soil erosion and seed washing in response to spring rain deluges. If the area is mostly bare soil that is prone to erosion (e.g., slopes), the site should be top-dressed by lightly scattering either straw (make sure you have a reliable weed-free source), compost or straw/paper blankets.

Mulching newly planted seedbeds helps to retain moisture, moderates temperature, and reduces erosion (i.e., movement of seed and soil off-site due to heavy rain events). Straw comes in bales of cereal grains (e.g., wheat, rye, barley or oats). Any small amount of cereal seed present will actually be helpful. Grains germinate fast and help to hold soil in place, yet plants die out quickly when mowed. Straw should be applied/sprinkled to ensure there are sufficient openings to the soil surface, which allows for sunlight penetration. Too much straw could promote disease or cause weak and spindly growth; whereas too little will not help retain soil moisture or prevent erosion. Rates of 80 to 100 lb straw per 1000 sq.ft. (a bale weighs about 35 lbs). Steep slopes may require more straw, and in some cases netting or string-tie-downs to hold straw in place. Straw should be raked /blown or otherwise removed once stands have good density.There also are numerous “straw blanket” products on the market, which often are utilized by professionals when soils get cold from late fall (Nov.) to early spring (March). On severe slopes, and in water drainage patterns and swales, straw blankets may be the best option in preventing excess erosion. Straw blankets are weed free, effective and should have at least a six-month durability onsite; hence, they are much more expensive to use versus straw bales. For small patchwork, yard trimming composts are effective (e.g., LeafGro). Simply apply about one inch of compost over bare areas; apply liberal amounts of seed (like peppering a steak); rake seed in and lightly tamp.