Do You Have to Kill Old Grass before Laying Sod?

Lawn work can be difficult, and if you don’t have much time or the energy to sod lawns that need it, you might look into shortcuts to fill those dead patches. Since the grass in your yard may already be dead and dead plants are nutrients, what is the harm of placing pieces of sod directly on existing pieces of turf?

Surprisingly, Dead grass may not come back but still can cause problems for new plants trying to grow, including sod pieces.

The grass isn’t the only organic matter that needs to be considered when laying sod, as weeds and pests can be lurking in your yard. Laying new sod on a weedy lawn or a dead lawn may result in even more turf troubles. Read on to figure out what to do with dead grass in your current lawn before laying the sod for a healthy lawn.  

How to Place Sod Over Previous Grass?

It is not advisable to lay sod over an existing lawn as it can make the new sod fail, resulting in wasted time and money and an unsightly turf situation. Grass that comes from sod farms is usually guaranteed to a certain extent to be pest and weed-free, but if you immediately drop it on existing vegetation, you could invite invasive grasses, weeds, and pests, right into your new turf.

Since new sod is still building a deep root system, herbicide, and pesticide options are limited, and you may not be able to restore the lawn without killing the sod.

For sod to root effectively, it needs direct soil contact, and the dead blades and matted roots of dead grass can act as a barrier against new root penetration.

Even adding fertilizer to grass may not give keep the sod alive long enough to push through the deeply-rooted lawn to find the air pockets and loose soil particles needed to thrive. The roots will have to push several inches deep and strong enough to spread across the entire lawn. 

A lawn that has died is likely in need of soil rejuvenation, and a layer of dead grass sandwiched under a new sod lawn is not going to cut it. Dead grass naturally leads to compaction, and before using a sod cutter to place your pieces, you will need to build air pockets with soil aeration.

Create loose soil particles for the sod to grow deep roots and improve water retention. You can cut openings in sod around irrigation heads and clean them up with a lawn roller and lawn edger.                                                           

Effective Methods of Eliminating Lawn Weeds before Sodding

Once the dead grass has been removed, a few simple steps can keep weeds from growing while the sod is rooting. Areas like loose turf edges will let in seeds, moisture, and light and can be an easy place for weed seeds to thrive.

But before you go and spray your whole lawn with Roundup, check out some ways to kill weeds in your previous lawn that will make your soil healthier and not harm your microbial population in the chart below. 

Method	Process	Benefits
Sheet Mulching	Alternate layers of cardboard and quality topsoil or compost until you have 4 to 6 inches and let it break down, adding water and heat to speed up decomposition	This method kills all plants and builds soil fertility and microorganisms extremely quickly while allowing lawn owners to level or increase the height of their turf where needed
Scalp, Rake, Topsoil	A walk-behind mower set to the lowest setting possible kills the grass at the crown, a rake pulls up the weakened blades and dry roots and adds a layer of topsoil 2 inches tall or taller	No soil structure is destroyed, and microbe populations are not exposed to the harmful surface conditions as they are with tilling; the topsoil depth can prevent grass from resprouting while giving your fresh lawn a better chance
Scrape, Aerate, Compost	Using a flathead shovel or pull-behind scraping device, remove the turf at the root level, then use a broad fork or core aerator to work the grass clippings into the soil and cover it all with a thick layer of compost	Less work than raking and removing all of the grass clippings and additional nutrients for new sod from the compost but not ideal for a weedy lawn
Natural Herbicides	Natural solutions like hot water, vinegar sprays, scorching, and excessive fertilization can eliminate weeds and grass while having little effect on future grass and soil life	While the methods are lethal to existing turf, the lingering effects and toxic residue of commercial-grade lawn herbicide are not present, making it better for jumpstarting new turf installation than glyphosate

What Happens if You Lay Sod on Weeds?

When you lay sod over weeds, rain, and existing seeds may create an environment where invasive grasses and persistent broad leaves can thrive. If you do not take the extra step to remove old grass and weeds before new turf installation, then watering could lead to a weed outbreak.

While trying to get a green lawn, you must keep the lawn damp, and weeds from nearby flower beds can enter with lawn debris and invite weeds. 

To prepare a lawn for sodding, you will want to remove all weeds and apply ordinary lawn fertilizer. Too much fertilizer or not enough can lead to weeds outgrowing your new turf, but a heavily seeded lawn in combination with sod can prevent that.

New sod needs routine lawn care until it is established, and removing weeds before laying sod will make the soil healthier and build the way to a lush lawn. 

How to Get Soil Ready for New Sod?

The process of getting the soil ready for sod should begin well ahead of the planned delivery date. A well-planned sod installation can save you time and money and give you the best lawn possible.

Missing a step or rushing the work, on the other hand, can result in countless problems and the possibility of the sod not taking. If this happens, you may need to redo all the work and pay for everything again, to avoid that, check out the steps below. 

Remove the Grass

Dead grass and undesired turf should be cut short with a mower and raked, scraped, or turned under until there is nothing between new sod and direct soil contact. 

Kill Weeds

Before placing new sod, you will want to remove dormant weed seeds as dormant seeds may spring to life when fertilizer and organic matter are added and watering increases. Scorching, natural herbicides, and manual removal are all great ways to keep a single weed seed from invading your new sod. 

Aerate 

Grass root growth determines how quickly you have a healthy yard, and bad root development can lead to dead turf quickly. Adding air pockets and creating a better environment for turf to focus on the development of roots is essential and easily done with aeration.

If your current turf failed, you can improve your grass roots and increase the benefits of irrigation systems and heavy rain. 

Fertilize 

Once you are ready for healthy, weed-free grass, you can add a fertilizer that will provide nutrients to the soil and be there when the sod’s roots get there. Fertilizer can be applied as a liquid or granular pre-mixed formula, or it can come in the form of natural organic matter laid over the previous layer of soil.

If using synthetic fertilizers, rinse the salts from the soil before placing sod, or you could burn new roots; if using fertile soils to build nutrients, lay it just hours before installation of sod to prevent the new soil from accumulating weeds and pests. 

Irrigate

Prepare irrigation by soil testing for moisture and make sure every part of your new sod will get even watering. Over or under-watering sod that has freshly been installed can kill it or invite weeds to replace it. Make sure you know how to reach all areas of the lawn without stepping on the sod to prevent unnecessary compaction. 

Lay Sod

Once the yard is prepared, lay the sod and level it with a sod roller. The more time spent leveling and preparing the soil, the better the sod will lay, so shortcuts should not be taken here. Sod with no spaces and a tight intertwine will grow better than sparsely or sloppily placed pieces.

Add moisture once all the sod is in place. 

Lawn Care Routine

Keeping new sod alive requires more care than maintaining a mature yard. For at least the first year, you will want to monitor and adjust your routine to prevent any areas of sod from dying. Constantly adjust watering rates if you discover low wet points, and protect your lawn from stress by watering and mowing correctly during the active seasons.

Once your lawn has deep roots, it can handle stress, and you can start to enjoy the fruits of your labor in the form of lush green turf.