MULCH, HYDROSEEDING, AND PREGERMINATION OF SEED
, 8 min reading time
When irrigation is limited or unavailable, you may want to consider a mulch to aid in germination of grass seed. Newly germinated seedlings are very subject to desiccation in the first few days after the primary root emerges. This will continue for a week or two until the seedling has developed enough of a root system to obtain moisture from underlying soil. Small seeded species like creeping bentgrass can die in a single windy afternoon in the first few days following germination if they are unprotected.
The term mulch refers to many different materials that hold moisture and protect new seedlings without interfering with the germination process. One of the most common mulches for grass seed establishment is straw. Bales of straw usually used as animal bedding are generally available locally from farmers or sometimes from garden stores. The standard recommendation for mulching newly seeded grass is 1 to 1.5 bales per 1000 sq. ft. of seeded area. It should be distributed uniformly over the area so that no part of the site is covered with an excess amount of material. Straw is surprisingly effective as a mulch, even in regions with very limited moisture. The advantage of straw is that it is cheap and biodegradable. You can simply leave it on the area and it will break down quickly. There is no need to remove it later. The downside of straw is that sometimes it contains perennial grassy weed seed that can cause serious problems later on. Try to get the cleanest straw possible. Seed of oats or wheat may germinate from straw, but they go away quickly with mowing. If it is grasses like quackgrass and bromegrass in the straw, they can cause serious problems in the future. Rollup matts of straw may be available from garden stores. This can be very effective but will be much more expensive than bales of straw.
Excelsior is another form of mulch used for establishing turf (Figure 1). It is composed of wood fiber like that used in packing materials. It comes in matts of various sizes that can be rolled out on top of the seed bed after seeding is finished. It is very good for holding steep slopes like those shown in Figure 1. It is biodegradable, so it can be left on the site to break down naturally. It can also be removed after germination, dried and saved for another job. It is expensive, but not as expensive as redoing an eroded hillside. It is also weed free which is a big advantage over straw.
Figure 1. Wood fiber much that comes in rolls.
There are also a number of porous turf covers that can be used for establishment. Covering golf greens in the winter to protect them from winter desiccation is a common practice in the upper Midwest, northern US and Canada. These covers can also be used to cover new seed beds during establishment. These covers are not left on the turf to biodegrade. They are removed, dried and used again. They are expensive, but they work very well. In Figure 3, they are being used to grow in an entire golf course. This is a very expensive practice, but again, it is much less expensive than dealing with severe erosion from a heavy rain event just after seeding. They are removed as soon as the grass has emerged and can hold the soil against movement.
Figure 2. Mulching with permeable cloth on a golf course.
Occasionally, you will find straw mats with fertilizer and seed incorporated in the mat. You simply roll it out on the soil, water and forget it until the grass is up. My experience with these has not been very positive. They generally contain inferior quality seed. It is also hard to keep them in contact with the soil and the germination of seed is low. I recommend establishing the lawn in the regular way first and then putting mulch on top. It will work much better for you.
The next method of seeding involving mulch is hydroseeding. In this process, a large piece of equipment with a tank with internal paddles to facilitate mixing is used to form a slurry of water, seed, mulch, fertilizer, and a tackifier (glue) to hold the material together on the soil. This slurry is sprayed out on the seed bed. That is me in Figure 3 hydroseeding a new lawn at Reiman Gardens on Iowa State University campus.
This process is very effective, particularly if you are dealing with slopes that can erode. Success of course depends on the quality of the seed used in the tank, but you can control that by purchasing the best available seed and providing it to the contractor. Some hydroseeders made for use in roadside construction can spray the slurry up slopes that are 30 to 40 feet high and can establish grass on very steep areas that would be nearly impossible to establish in any other way.
Hydroseeders are very expensive and are generally only available through large landscape companies. You can hire them to seed a lawn. Unless you have some very steep slopes, I would recommend the standard establishment procedure for smaller areas like a lawn. Hydroseeders are generally a good investment for a college campus or city operations where a lot of seeding is done every year. There are distributors that provide professional grade mulch and tackifiers for use in hydroseeders. This is a hard process to do right and I would recommend using professional grade products in the equipment.
Figure 3. Your author hydroseeding on Iowa State Campus.
Figure 4 shows a new process called dryjecting. By this process, seed and fertilizer are combined with dry compost and sprayed out on the soil surface. This again requires very specialized equipment. It is not as good on steep slopes as hydroseeding but is very effective on normal lawn area and roadsides. I have had limited experience with this process, but what I have seen of it has been very positive. Again, the quality of the seed is vital to success.
Figure 5. Dry mulching with compost and seed.
Pregermination of seed is a method of speeding up establishment. It is generally used on golf courses and athletic fields to repair damage quickly. By this method, seed is soaked in water for a few days before seeding until germination begins. The mortality rate of pregerminated seed will be very high, so I do not recommend it for lawns or other normal situations. But in emergency situations, such as before a big game on a sports field, it does allow for more rapid establishment.
The following process is from the 4th ed. of my textbook, “Fundamentals of Turfgrass Management”. I got it from Mike Andresen (Certified Sports Field Manager), former athletic field manager at Iowa State University. Mr. Andresen uses it to pregerminate seed to fill in damaged areas on athletic fields where rapid establishment is a must. The procedure is as follows:
1. Begin with 50 lb of seed in a nylon bag.
2. Place the bag of seed in a 50-gal barrel and cover it with water. Then cover the barrel with plastic.
3. Each day remove the plastic and change the water.
4. On the fourth day, aerify the area to be seeded. Empty the water from the barrel and spread the seed by hand on the aerified area. Sand is combined with the seed for hand spreading. Calcined clay can also be used to dry the seed so that it will flow through a spreader.
5. Apply a starter fertilizer and Subdue™ fungicide to control Pythium.
6. Use a verticut to slice in seed and break up plugs.
7. Lightly rake the area and roll with a medium-weight roller (200 to 500 lb).
8. Water the area until the establishment is complete.
In situations where smaller amounts of seed are needed, seed can simply be placed in a bucket and soaked in water for three to four days before seeding.
Again, this is expensive and should be used for emergencies only. It is not necessary if you have sufficient time for normal seeding.
Nick Christians, University Professor of Horticulture, Emeritus, Iowa State University
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Fundamentals of Turfgrass Mgt. 5th ed http://www.wiley.com/WileyCDA/WileyTitle/productCd-1119204631.html
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