Seed Test Plots: Finding a Better Method

Minnesota winters present a number of challenges to our landscapes. Salt usage, deep snow piles, and the freeze/thaw cycle all contribute to one of these challenges called ‘winterkill’. Winterkill is used as a general term to describe grass (ie. turf grass, hereby referred to as “grass”) that has died over the winter, possibly due to the causes described above. Living in our climate, winterkill is an unfortunate and inevitable problem that we must tackle each spring to some degree. Over the years, Horticulture Services has tried a number of different methods for winterkill grass repairs, with the two main methods being sod and grass seeding. Sod certainly has its merits, but presents its own problems with its high cost, high labor, and high water needs. This increasing cost of sod meant it was not always a viable option for our customers, so we found it important to develop and implement a worthwhile and economical go-to grass repair option. Through testing it became clear: Seeding is the most versatile, hassle-free, and cost-effective option for winterkill and most all grass repairs. However, this fact had not always been clear to us, as seeding had historically brought inconsistent results.  Arriving at our new conclusion regarding seeding took a handful of years, careful observation, and many seeding test plots.

In the fall of 2014, we began taking a closer look at our seeding methods. We knew that seeding worked, but we wanted to make it work in a variety of situations and locations. To explore this, a trial area was created in an open space with bare topsoil and regular irrigation. The primary variables we were looking to test were: soil amendments, mixtures, and seeding media. Prior to these tests we had already found a seed mixture that had performed really well for us which contains equal parts Kentucky Bluegrass and Perennial Rye. We also had success using compost in our seeding process so we chose to focus on the use of standard compost in many of the trials. Our hope from testing was to develop an easy-to-use product that would work in multiple situations and give us consistent results. Our tested soil amendments included the use of standard compost, a compost blend, and pulverized topsoil (black dirt).  The use of a seed media or seed-aide was also tested. Seed-aide is a paper mache-type material which accomplishes a couple of things. It first absorbs and retains water which in theory would be available for the germinating seed. It also coats the surface of the area which helps to prevent the top layer of soil to heat up and dry out as quickly. The last variable we set out to explore was how the seed was distributed. We either chose to sprinkle the seed over the area and let it rest on top, or we physically mixed it into the soil. To keep each test consistent, the same volume of soil amendment was spread out over each test plot, the same seed variety and amount was used, and each of these areas was also irrigated equally and by using the same method. Lastly, we repeated our testing plots three times to ensure we received consistent results.

Below is a table representing our 6 seed plots from 2014:
Jeff-WilsonWhile our first set of trials were simple with few variables, they offered up clear and concise results. Within five days we began seeing signs of germination within many of the plots. At day 12 it became clear that the standard compost with seed mixed in was our front runner. While the other test plots had some patchy tufts of grass coming up, the plots with the mixed compost and seed were nearly full of young emerging grass shoots. Our final results showed that compost was the best soil amendment over blended compost and topsoil. We also observed that a growing media such as seed aide used in this manner had little positive effect on germination and establishment of our seed. Lastly, our major takeaway was that mixing seed into the compost was by far the most beneficial practice we tested. After seeing these results we then implemented this method of seeding for the repair of winterkill the following spring.

Jeff-WilsonOur seed test plots showing repeating consistent results, 2014 | Photo Horticulture Services

Jeff-WilsonCreating our seed test plots, 2014 | Photo Horticulture Services

Jeff-WilsonCreating our seed test plots, 2014 | Photo Horticulture Services

Jeff-WilsonOur seeding method showing great results at a client’s property | Photo Horticulture Services

Over the next few years we used this method of seed mixed into our standard compost and saw much success with it. Knowing that this method worked under ideal conditions we continued using it while refining our process and timeline of installation. In the fall of 2018, we wanted to see if we could further the success of our method. We began looking at materials which could supplement our compost/seed mix method. Going into the process we knew that keeping the seed and compost damp was crucial to getting successful germination. Knowing this, we wanted to explore ways to either keep our seed damp and or covered. Our goal during this set of trials was to explore the use of erosion blanket, hydroseed, and a wetting agent. Erosion blanket is a thin layer of either straw or a ground-down fibrous material woven into a poly netting. It works by covering an area and preventing wash out. In our case we were interested in the shading effect it could have on a seeded area. Hydroseed is a similar product to the seed-aide that was mentioned in the previous test. Hydroseed consists of a fine paper-like product which is then wetted, mixed with seed, and applied to a given area. Lastly, our wetting agent was being tested for its hydrophilic properties. A wetting agent works with water in a way to help keep and disperse the available water for our seeding. All of these were being tested against our control, which was our standard mixed regular compost and seed. Instead of taking place on bare soil like with our previous set of trials, these trials were set up on dead grass to better mimic an area of winterkill. We also repeated our testing plots three times, but with full irrigation, part irrigation, and no irrigation. Like with our previous trials, we used equal quantities of soil, seed, and used the same seed variety.

Below is a table representing our 6 seed plots from 2018 (control not shown): Jeff-Wilson

This set of trials made it abundantly clear how extremely important supplemental watering was to our seeding process. In the testing plots which were partially irrigated or not irrigated at all we saw very little seed germination. We already knew water input was important, but after seeing this set of trials it made it clear to us that simply relying on rain was not a sufficient enough water source to get consistent results. Looking at the test plots which received full regular irrigation we saw a mixed bag of results. Hydroseed showed the most promise of all of our tested variables. The most germinated plots were the ones with wetted hydroseed, on both bare compost and dead grass. Our wetting agent plot showed the second most promise, but had significantly less germination than our hydroseeded areas. While hydroseed proved to be a viable option, we concluded that it may not be the best fit for our context of application. Hydroseed is quick and easy when applied by a machine over a large area, but not so quick and easy when applying to small patches like we commonly do. Our small scale method for testing included hand wetting and mixing the hydroseed media which would not be an easily managed practice on the job site. The erosion netting also showed some promise, but fell into the same category as hydroseeding in that it may not be the most practical for small areas like we are repairing. Erosion netting works wonders over a large area, but requires sod staples to secure it to the ground and each portion to be cut to size to fit a particular area. Once again, our standard mixed compost and seed proved to be a reliable and easy to replicate method for grass repair. The wetting agent, which we had been the most excited about, didn’t show us enough promise to become our new everyday seeding practice. This set of trials also solidified our previous notion that irrigation and the right conditions are essential for full germination.

A year prior, in 2017, a similar set of trials were set up to explore the use of wetting agents, hydroseed, and a peat moss amendment. Unfortunately, the fall of 2017 proved to be a hot and dry period which was not conducive to seed germination even with regular irrigation. Although we weren’t able to fully test another set of variables, it did provide us with results. It showed us that sometimes even in the correct time window conditions can be erratic enough to not allow for great seed growth. Each of our three trials were performed in the fall within a timeframe which we refer to as a ‘seeding window’. This seeding window typically gives us ideal growing conditions to reliably germinate grass seed. There are generally two consistent seeding windows each year. One in the spring which occurs sometime around late April to mid-May, and a second in the fall which usually occurs around mid-September to early October. The key during these times is temperature. A pleasant spring or fall day provides enough warmth and high sunlight to germinate seed without getting too hot and burning the seed or robbing the soil of all available moisture. Seeding is certainly possible outside of these seeding windows, but we have found seed will most reliably germinate at a consistent high rate within these set time frames.

The few sets of trials we have performed have allowed us to explore different products and practices that may be applicable to our needs. These trials have shown us what doesn’t work, but more importantly they have given us a reliable repair method and have reaffirmed that our method of grass repair using seed works reliably in a variety of settings and situations. The results can easily be replicated all over a property in areas large and small. As new technologies and products present themselves, we plan to continue to trial and test different products and methods that best fit our needs. Trialing and innovating within our ever-changing industry will allow us to continually provide the best and most reliable product for our customers that we can.

Brian Davis | Account Manager
Posted 4/13/2020