Q: How soon can I seed this spring, and do you have any tips for me?
A: Cool-season grass seed germinates best when the soil temperatures are between 50-65 degrees F. If we look at Ohio, soil temperatures are consistently above 50°F by early April; however, there may be circumstances where getting the seed out a little earlier is warranted. Applying the seed in winter as a dormant seed ensures the seed is in place and ready to germinate when conditions allow. The advantages of dormant seeding are that soils are sometimes drier and easier to work, there might be more people available to do the job, and the seed may germinate earlier than a conventional spring seeding, giving it a competitive edge over crabgrass and other spring weeds. The disadvantage is that seed mortality is 30-50% higher, particularly if the seed germinates and then there’s a late spring frost. So it’s somewhat of a gamble, but one you might choose to make.
With any type of spring seeding, the key is to have seed down before mid-April when crabgrass germinates. Weed pressure in spring is a challenge, so ideally the seed operation would also include an application of a preemergent herbicide that controls weed seed germination without adversely affecting the grass seed. An application of mesotrione or siduron on the day of seeding, or an application of topramazone the day before seeding, should provide good weed suppression. Be careful applying other preemergence herbicides that might impede grass seed germination. Weed pressure is so great in the spring that repeat applications of preemergence and/or a postemergence herbicides may be warranted.
Another important point to make with any spring seeding is to avoid, if possible, disturbing the soil. Achieving good seed:soil contact is possible without disturbing the soil with equipment like slit-seeders, and fraze mowers. Cultivating the soil in spring opens up the weed seed bank and brings weed seeds up to the soil surface where they germinate. Weed seeds can remain viable in the seed bank for many years. The main source of weed seeds in the seed bank is from local mature weeds that set seed, so it’s important to control weeds like crabgrass, goosegrass and Poa before they set seed.
Unfortunately it is not possible to build up a seed bank of desirable, domesticated grass seed in the soil. For a viable seed bank to build up, the seed must be in the soil but not subject to the germination triggers, i.e., moisture and warmth. It is highly unlikely that seed that has been broadcast or slit-seeded into the soil surface and subjected to rain or irrigation wouldn’t germinate. This makes sense, when you think that we store grass seed in cool, dry places to prevent it from germinating or rotting. Biological seed bank management as a tool for sustainable weed management is not a topic that’s discussed a lot, but maybe it should be.
Seed rates and plant health are also worthy of a mention. It’s important to seed at the recommended rate for the turf species. While “more is better” is tempting, particularly if there are spring deadlines to meet, the long-term success of the turfgrass plants relies upon having space and resources to fully develop and mature. In essence, larger plants have increased wear tolerance.
Sod farmers will generally seed at, or just below, the recommended seed rate for a good reason. The turfgrass plants will not just grow, but will develop tillers, stolons and rhizomes that are critical during harvest. Those tillers, stolons and rhizomes are also critical for the long-term health of the plant and its ability to withstand athletic field traffic and wear. If seed rates are too high, the seedlings will be weak and susceptible to disease, and as they mature they will reach a carrying capacity within their community where they start to self-thin. A good example of this is crabgrass; in spring there are lots of tiny seedlings, but by the end of the season only large, singular plants remain. The crabgrass plants have competed with each other and self-thinned because they can only grow at the expense of others, otherwise known as survival of the fittest.
Ultimately, the most successful plants in the sward are those with quick germination, seedling vigor, the greatest density, and good tillering capacity. Turfgrasses with endophytes also have an advantage. It’s not surprising then, that perennial ryegrass dominates and monopolizes resources, and why it’s hard to get Kentucky bluegrass established in a mix where perennial ryegrass is greater than about 30% by weight.
One last point to make is that seeding is not successful on areas that already have a full, dense cover of turf. Years of research have shown us that you cannot change the species composition of an established sward by applying seed. In other words, if the field is comprised of a thick healthy sward of tall fescue, overseeding it with another species will not work. This is due to the exclusion of light in the turf canopy and the existing competition for below-ground resources. The turf sward must be thinned and soil exposed for the new seed to have a chance at germinating and establishing.
There are other tools to aid seed germination and establishment that I have not included but are worthy of more investigation. These include using pre-germinated seed, using seed coats that retain moisture or are pre-loaded with nutrients or fungicides, irrigation syringing cycles, starter fertilizers, the use of growth blankets, supplementary light racks, and frequent, high-quality mowing. As a sports turf manager, where fields are constantly under renovation, every little bit helps. Good luck!
Pamela Sherratt is a turf extension specialist and lecturer at Ohio State; her “Q&A” columns appear bi-monthly in SportsTurf magazine.