Seeding Your Lawn in the Spring
March and April, when the relief of spring seeps into our gray-tinged winter lethargy here in Pittsburgh, PA, is when we get inspired by our lawn and garden. Bright green starts to show itself and new growth is evident as soil temperatures rise and plants re-emerge. As the Turfgrass Specialist here at Cavacini Landscaping & Garden Center, it is when I get the most questions about grass seed and overseeding of customer’s lawns.
Bald spots in the yard, damage spots from pet urine, and overall thin turfgrass cover are the conditions that I hear customers most frequently ask about improving or recovering. The preparation and process are the same for all those scenarios. But, before you pull out the tools, timing is imperative to success. Turfgrass seed is not going to germinate until soil temperatures are regularly hovering around 55 degrees F. And that’s a minimum soil temperature for Kentucky bluegrass and fine fescues. Tall fescue and perennial ryegrass don’t do much until soil temperatures are closer to 60 degrees F. I’ll come back to the different species of turfgrass later, but for now, the key takeaway is that soil temperature drives germination. We do not consistently achieve that until approximately mid-April here in Pittsburgh, PA.
With that point made, preparation of the area that you’d like to seed, or seedbed preparation, is the most important factor for success. The new grass seed must be pressed into contact with soil. Using a rake, or any cultivation tool you prefer, remove all the loose organic debris, dead grass, and leaves covering the soil. Once all of the debris is gone, scarify, or scratch, the soil to a depth of at least ½”. Try raking in two or three different directions to loosen the top layer of soil. Once you have a smooth, lightly cultivated soil area, the seedbed is prepared. Nothing else is required. However, adding a thin layer of new topsoil at this stage is an opportunity to improve your seedbed or level the area.
Next, sprinkle your grass seed over the prepared seedbed. Seeding rates for a new lawn, meaning it’s completely bare soil and you are starting with zero grass, range from 4 to 7 pounds of grass seed per 1000 square feet. For overseeding, meaning you have some grass present, and you want to introduce more, the rate is about half. Or 2 to 4 pounds of seed per 1000 square feet. Often, we are “spot seeding” bare areas among what is an otherwise decent lawn. These spots are often only a couple square feet and calculating seed rates is rather futile. Pictures are always better than a written description and Albert Lea Seeds has a great example of how seed should look at the correct rate. The point is to avoid seeding too heavily as it is NOT advantageous. Once the seed is down, lightly tamp or walk on the area to press the seed into the soil.
Here is where I will briefly loop back to grass species selection. Almost all residential lawns perform best with a seed mix. This means three or four species mixed together in the bag of seed. Kentucky bluegrass, perennial ryegrass, tall fescue and fine fescue are the cool-season grasses suited to grow in our region. They all have pros and cons related to their appearance and maintenance needs, but when mixed together, the species most suited to the conditions present will tend to dominate. For instance, the slightly more shaded areas of your lawn will usually end up being mostly tall or fine fescue. Sidebar: turfgrass does not grow in deep shade. Other groundcovers or perennial plants can live in particularly low light but turfgrass is not one of them. Kentucky bluegrass has the darkest green color but only thrives in full sun. Perennial ryegrass has the absolute toughest seedlings that can survive foot traffic even before it is mature. Yards with pet traffic often end up having a high population of perennial ryegrass because its seedlings are the only ones that reach maturity. For these reasons, I will always recommend a mix of turfgrass species for home lawns.
After the seeding process is complete, add a starter fertilizer. Starter fertilizer gets its name because it is ideal for seed germination due to a high ratio of phosphorus. Fertilizers have three numbers on the bag that are always expressed in the same format of NPK or nitrogen (N), phosphorus (P), and potassium (K). The numbers, for example (9-18-12), correspond to the percentage of the nutrient by weight. In the example I gave, there is 18% phosphorous by weight. It is the phosphorous that is most important to successful grass seed germination but the other nutrients are needed as well. Starter fertilizer normally lasts about 4 to 5 weeks by which time your seed should be germinated, and the young seedlings will be ready for another light feeding with a balanced fertilizer to help them reach maturity.
To cover or not to cover? The answer is that your new grass seed does not need to be covered in order to germinate or grow. However, a light covering at the time of seeding can help in a few different ways. Covering the newly seeded area can help prevent washouts during heavy rain, will help slow down the drying of soil so your watering interval is less frequent, and to some extent a covering can help keep the seedbed warmer to aid in faster germination. A covering can consist of many different materials. Traditionally, folks used straw and that is still a viable and inexpensive option. The downside of straw is that it often contains weed seeds that end up competing with your desirable grass plants. A better choice is a light (1/2” or less) covering of mushroom manure or compost. There are also many commercially produced seed coverings that consist of recycled paper products and work quite well.
The newly seeded area needs to be kept consistently moist from the time of seeding all the way until the new seedlings have been mowed at least 3 times. How much water and how often always generates a lot of questions. I created a separate factsheet about this topic that you can find on our website’s Resources page (it is also available for download as a pdf.)
But, of course, there are a few caveats when seeding in the spring. In the previous paragraph I talked about watering requirements. This is often the most undesirable part for homeowners. Assuming you seed in April and have a nice covering of new seedlings in May, that young grass now has to face the heat of summer in June, July and August. It is very likely that it will need extra water throughout the entire first summer to become mature enough to withstand normal bouts of heat and drought stress.
The other biggest hassle when spring seeding is competition from crabgrass and other annual weeds. These annual weeds are different from perennial weeds like dandelion and clover which can be treated later in the summer when the young grass seedlings are mature enough to withstand herbicides. Crabgrass and goosegrass are easy and inexpensive to manage preventatively. They are much more difficult and expensive to manage post-emergently, or after you have them. When you spring seed, you cannot use the traditional crabgrass preventive products. There are some specialty products, mesotrione or quinclorac, that can be applied at the same time you put down the grass seed to provide 30 days of crabgrass control. This is not enough for season-long control, however. Also, these products are not easily obtained in small quantities reasonable for homeowners.
These caveats, among a few others, are the reasons why spring seeding of lawns is not ideal. If you can wait until early September, that is the ideal time in our region to install a new lawn or overseed your existing lawn. Jonathan Green, a well know seed company and the brand of grass seed that we carry in the Garden Center, has an expanded explanation on their website. Of course, it is not always possible to avoid spring lawn seeding but waiting until the early fall significantly reduces the watering imposition and completely removes the headache of crabgrass and goosegrass encroachment. Please reach out to me if you have additional questions about seeding or lawn care.
Seeding Your Lawn in the Spring
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