Lack of sunlight or a shaded environment

The most common problem when the grass isn't growing in certain areas is a lack of sunlight.  Landscapes mature over time, and what was once a sunny garden with a lush lawn could now be struggling. Trees and hedges, having grown in size, will now cast a shadow on your sun-loving lawn, causing it to perish.  The same thing will happen if you plant grass under existing trees and hedges if they are blocking too much sunlight.  The good news is there are many varieties of grass seed, some requiring 8 plus hours of sun and others handling limited light.  Your options will be to replace the lawn in that area with a grass not needing as much sunlight, bring your beds out further to cover the area and plant shade-tolerant plants, or just cover the bed with bark or mulch if you prefer.  You can also try increasing your mowing height a little bit in the shaded areas.

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Competition from tree roots

Grass near tree roots or even large shrubs may grow patchy and be noticeably poorer than in other areas.  This is because the grassroots are competing with the larger tree roots for water, nutrients, light, and space. With the tree and shrub roots being that much bigger, in the desperate fight for life-essential elements, the grassroots just aren't going to win. The solution is similar to our previous issue, lack of sunlight, build your beds out further or cover the area with mulch instead. 

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Compacted soil

Soil compaction can cause major problems for grass growth as it stops oxygen from getting down to the roots. Like us, grass needs to breathe. In compacted soil, the oxygen's ability to move through pores within the soil down to the roots is severely limited. It usually occurs due to a lack of preparation of the ground before turf is laid. This commonly happens on new build sites where they leave the garden till last and just throw a few inches of new improver on top and mix 3 or 4 inches deep.  The grass then grows close to the surface so it isn't starved of oxygen, making it susceptible to environmental stresses like heat and drought. The deeper the grassroots can grow, the better as it gives them more access to water and nutrients. 

 

Another sign you have compacted soil is if you have a large tree and its roots are growing across the surface instead of down (if they could grow down, they would). As you can probably imagine, the large roots will also further compact the soil as well as steal space, water, and nutrients, further hindering the grass's success. The way to solve the issue is aeration. The best time to do it is the day after it has rained. The tools most commonly used are lawn aerator shoes, hand aerators, and machine aerators. You can leave the leftover soil plugs on top afterward as they will decompose back into the grown. Once finished, it is a good idea to apply a layer of top-dressing which will add vital nutrients and improve your soil structure. You may need to do this once or twice a year, depending on how compacted the soil is.

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Underground objects

One reason for grass not growing which may surprise you is underground objects. These can be in the form of granite or buried construction material or just hard clay.  Again, the grassroots will stay near the surface, making them vulnerable.  There is no easy fix to this problem, unfortunately.  Other than digging up your lawn and starting again, you can try core aeration. However, this may not solve the problem and you may just have to work around the issue. 

 

Lack of airflow

The final issue usually occurs in small gardens surrounded by Leyland cypress. Often planted to solve privacy problems it can cause a lack of aeration, giving you another dilemma. The lack of airflow can make the air stagnant because there's little-to-no air movement. Your grass will have an increased risk of disease and thus dying. The only options you have are to limb-up trees to help with aeration or place fans around the garden (which is the more expensive and impractical option!)