Renovating a Tired Lawn Without Starting Over

Why did my lawn get thin in the first place?

Diagnose before you seed. CSU's PlantTalk on patchy lawns says thin grass is often a sign the lawn has not had enough fertilizer or water, the soil is too compacted, there is too much wear, or there is a disease or insect problem, and that pests are usually the least common reason while improper fertilizing, watering or mowing are the most common. CSU says to diagnose the cause first; seed thrown onto a lawn without fixing the cause thins out again.

Walk the lawn with a few questions. Is the thin area under a tree that has grown bigger? Is it a sprinkler dead zone? Is it the path to the shed or the dog's route? Is the soil hard enough that a screwdriver will not go in? Is there more than half an inch of thatch? Each answer points to a different fix, and our guides to mowing height, thatch and lawn insects cover the common ones.

What are the options short of starting over?

Three levels. First, change the care: Montana State University Extension's lawn guide makes the point that mowing at 2.5 to 3 inches, deep infrequent watering and fall-weighted fertilizing are what keep turf dense, and CSU says routine lawn management will thicken grass back up once the cause is fixed. Second, overseed thin areas. Third, partial renovation: CSU defines it as core aeration and overseeding to thicken thin turf and introduce better-adapted grass varieties.

Partial renovation keeps the existing lawn, its roots and its soil structure, while adding new plants into it. The lawn stays usable, and the change happens over one or two seasons instead of starting from bare dirt.

How does partial renovation work?

Core aerate hard, then seed into the holes. CSU's renovation note recommends thoroughly core aerating, perhaps with two passes at right angles to get more holes than usual. Seed must contact soil and stay moist to germinate; it will not germinate resting on a mat of grass leaves. Seed that falls into the aeration holes gets soil contact and protection from drying sun and wind. MSU agrees that overseeding after aerating improves seed-to-soil contact, and suggests a thin (1/4 inch) layer of compost after aerating on poor soils.

Then water lightly and often. CSU says to keep the seed moist through the roughly 21-day bluegrass germination period with brief waterings several times a day depending on temperature, and warns against overwatering, which wastes water and harms the roots of existing grass and trees. Our guide to when to aerate and overseed covers the equipment and steps.

When is the best time to renovate in Montana?

Late summer into early fall. MSU says seeding in mid-August to mid-September is better than spring, because annual weeds do not have time to seed and the grass gets fall and early spring to establish before summer. CSU names September as a good overseeding month and says overseeding in spring and fall both speeds the process. MSU says to aerate when turf is actively growing, in spring or fall, never when dormant, and when the soil is moist.

One timing conflict: CSU warns that a spring crabgrass preventer will kill seedling grass, so if one was applied, wait until August to seed. Our guide to new lawn timing in Montana has the full calendar.

Which seed should I use when overseeding?

Something compatible with what is there, and better suited to the problem spot. CSU says to choose a species compatible with the existing lawn. For lawns thinning as trees grow, CSU suggests newer shade-adapted bluegrass and fine fescue, and MSU's shade mix is about 60 percent creeping red or Chewings fescue. For full sun, CSU mentions Texas by Kentucky hybrid bluegrasses for heat tolerance and deeper roots. Where billbugs have been a problem, MSU notes that endophyte-containing perennial ryegrasses and fescues can be highly resistant.

Avoid mismatches: CSU warns against dropping pasture tall fescue or annual ryegrass into a bluegrass lawn. Our guide to Kentucky bluegrass versus fescue explains how the species fit together.

When is starting over the honest answer?

When the problem is the grass itself, the soil or the grade. CSU's PlantTalk on roughstalk bluegrass says no selective herbicide removes it from a bluegrass or ryegrass lawn, so homeowners must either live with it or kill and reseed or resod the whole area. CSU says the same logic applies to a lawn severely infested with perennial grassy weeds: renovation can begin by spraying the area with a non-selective herbicide, then working and seeding or sodding three to four weeks later.

Grade and soil problems also call for a rebuild. MSU asks for at least a 1 percent slope away from the house, and says that if you change the grade you should remove the top 6 inches of soil, regrade, then replace the topsoil. Water that sits against a foundation, or lawn on a few inches of soil over cobble, will not be fixed by overseeding. Our guides to sod or seed and standing water in the lawn cover the rebuild.

Is power raking part of a renovation?

Only when thatch is severe, and then it is the renovation. MSU says mechanical dethatchers and power rakes should only be used when thatch has become excessive, because dethatching causes severe damage and is roughly equivalent to renovating the lawn. MSU says that where thatch is heavy or soil compacted, aeration gives quicker results, and that both must be followed by reducing nitrogen and/or irrigation so thatch does not rebuild.

What does renovation not fix?

Care habits. If the lawn thinned because it was mowed short, watered lightly every day or fed heavily in midsummer, new seed will thin the same way. MSU notes that frequent light watering produces shallow roots and favors annual bluegrass and rough stalk bluegrass. It also will not fix deep shade; CSU says that in heavy shade, ground covers or wood-chip mulch with shade-loving perennials may be more practical than grass. Our guide to replacing some lawn with native plants covers that route.

How long until a renovated lawn looks good?

Longer than a new sod lawn, shorter than people fear. CSU says new grass emerges as plumes from the aeration holes and spreads over time, and that fully introducing better-adapted varieties this way may take several years, which is why it suggests overseeding in both spring and fall to speed the process.

Keep foot traffic and dogs off newly seeded areas through germination and the first few mowings. Mow when the new grass reaches about a third above your target height, removing no more than a third of the blade, as MSU recommends for all lawns.

Can I combine weed control with renovation?

Yes, with sequencing. CSU and MSU both favor fall for perennial broadleaf weed control, and fall is also the seeding window, so the two have to be scheduled around each other and the product label, which sets how soon seed can follow an herbicide. Where weeds are heavy, a common approach is to treat in late summer, then seed into the gaps once the label allows; where they are light, digging them during aeration and reseeding the holes avoids the conflict. Our guide to common lawn weeds in western Montana helps identify what you are dealing with.

What should I ask a lawn company about renovation?

What do you think caused the decline, and how will the plan address it? How many aeration passes, and how close will the holes be? CSU's aeration note says a single pass often leaves holes several inches apart and does little. What seed, and why that mix for my shade and use? Who handles the germination watering, and how will the sprinkler schedule change? What fertilizer and weed control follows, and when? Our guide to what drives the cost of a lawn care program explains how those choices affect the scope.

Lawn renovation with HJ

We start with a look at why the lawn thinned, then match the fix: aeration and overseeding for most lawns, sprinkler repair where coverage is the cause, and a rebuild through our landscaping work when the soil or grade is wrong. Our licensed fertilizer and weed control program keeps the result thick. This guide is part of our Montana Landscaping, Lawn & Irrigation Guide. Call (406) 215-7319 or request a free estimate.

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