It seems obvious that grass grows in daylight, but actually, it grows all the time – yes, even at night. The rate of growth isn’t consistent, however, and environmental conditions play a big part. Let’s unravel the mysteries of how grass grows and examine ways to optimize its growth.
Grass grows continually when not dormant. As long as the grass receives at least four hours of sunlight during the day, it can produce excess energy and carbohydrates that create new plant material. The grass processes these reserves overnight; the fastest growth typically occurs just before dawn.
Overview of How Grass Grows Overnight
Grass grows about two to six inches a month, depending upon the species. It’s easy to assume grass only grows while the sun shines, but actually, it’s growing all the time.
While grass does grow during the day, not all the energy and sugars it manufactures through photosynthesis are consumed immediately. In normal sunlight, the plant typically creates more energy and building elements than it can use during the day.
These excess sugars and other chemical products are stored as reserves. This allows your grass to continue building new plant growth after the sun has gone down. The plant processes this material at night and recharges its reserves during the day.
Understanding the mechanics of how your grass grows lets you work in harmony with its natural cycle of production.
How Grass Grows
Photosynthesis is a complex series of organic chemical reactions that convert light into physical matter. This amazing process combines absorbed sunlight along with water, carbon dioxide, and small amounts of other elements to produce glucose and oxygen.
The plant releases the oxygen into the air and uses the manufactured glucose for the production of carbohydrates. This material is further processed into new cells, pigments, and various compounds used within the grass’s system.
As its blades absorb sunlight during the day, your hard-working grass is building up reserves that it will process through the “rest” period of darkness. This means your lawn doesn’t quit when the sun goes down: it’s up all night, busy processing the day’s sunshine.
In fact, one of the fastest periods of growth is just at dawn, after the grass has digested the glucose and is resetting for a new day of photosynthesis.
Making Hay While The Sun Shines
Four hours of sunlight is the minimum amount needed by most grass species to survive. In that situation, the plant can’t produce a surplus of energy to grow. In practice, grass would quickly go dormant in this situation: otherwise, sun-deprived grass would yellow and die as its energy and reserves dwindled.
When it receives more than four hours a day, your lawn will create a surplus of glucose for repairs and new growth.
Your lawn doesn’t require four hours of intense sun; grass can photosynthesize and build reserves on cloudy days, too. Some grasses even thrive in shade, depending upon the species.
Photosynthesis And Respiration
Photosynthesis uses two sets of biochemical processes called the light reaction and the dark reaction. These two processes give a plant more flexibility in how it uses available light.
Light Reaction – This process absorbs light and transforms it into energy the plant can use. Light reactions can only happen in the presence of light. The energy it creates is unstable and breaks down quickly, so it can’t be stored for later use: the plant has to use energy created by the light reaction immediately, or it will be lost.
Dark Reaction – To balance out the need to use energy immediately, dark reactions convert the short-lived energy created by a light reaction into carbohydrates that can be stored for later processing. Dark reactions can occur under illumination, but light isn’t necessary. Dark reactions may happen at any time.
Plants use photosynthesis to produce the raw elements they need to live and grow, but that’s not the full story of growth. Respiration is needed, too: it’s the part of the cycle that actually creates new plant parts.
Plants respire? Well … at least they exhale. Respiration is the output of a chemical process that combines products created by photosynthesis with water and carbon dioxide. This reaction set creates complex carbohydrates necessary for growth. The end-product of oxygen is released after formation … and so the plant “breathes.”
In daylight, tiny chlorophyll-containing organs on the grass blades called chloroplasts absorb light and produce energy the plant can use. At night, the chloroplasts close, shrink, and shut down as photosynthesis stops … but respiration can continue.
Darwin’s Theory Of Nightime Growth
Charles Darwin predicted that plants grew at night. He actually thought they would grow more quickly at night than in daylight. His theory was that a plant would grow faster in low light in hopes of reaching better conditions.
Today we know that plants do indeed keep growing at night and grow fastest in the hours closest to dawn … but it’s probably not for the reason Darwin surmised. It’s true that plants in chronically low-light conditions can bolt and stretch for light, but they don’t do this regularly every night.
Instead, your grass grows fastest just before dawn to consume the previous day’s energy that was processed overnight. The early growth spurt is essentially when your grass is clearing its decks before a new cargo of sunlight arrives.
Factors That Affect Grass Growth
Grass grows continually but does so at different rates. The speed is limited to how much energy and sugars the plant can produce through photosynthesis.
Photosynthesis is understandably affected by the amount of light it receives, but other factors also influence grass growth:
Lawn grasses are categorized into warm-season or cool-season varieties, depending upon the seasons and temperatures in which they grow best.
Cool-season varieties grow best in the spring and fall; warm-season species grow better in the hotter months of summer. Both kinds of grasses are often used together in a single lawn to keep the turf green year-round.
The growing seasons of each category overlap a bit – neither type of grass grows in frigid winter; they go dormant instead. Cool-season grass springs up quickly in the spring, but warm-season grass isn’t far behind and hits its peak only a month later.
The fundamental difference between the two lawn grass categories is their preferred temperature range. Warm-season varieties can remain green and growing in the hot summer sun that puts its cool-season cousins to sleep; conversely, warm-season grass heads for the exits in the kind of autumn weather a cool-season turf loves.
Warm-Season Grass – The peak of production for warm-season grass is at a temperature between 90ºF (32ºC) and 95ºF (35ºC). Most will stop growing when the thermometer dips below 55ºF (13ºC).
Cool-Season Grass – The optimal range for cool-season grass is about 65ºF (18ºC) to 75ºF (24ºC), but they don’t stop growing until temperatures drop below 40ºF (4.44ºC). Cool-season grasses need more water than warm-season types; in hot weather their growth slows and they enter dormancy.
Moisture And Humidity
Water is a critical factor of grass growth. If you’re looking for speedy production, keep your lawn well-hydrated (but never soggy!)
Dormancy comes naturally to either category of lawn grass, and dry conditions are one of its triggers. In good growing weather, simply watering the grass can make it green up again.
Like most plants, grasses generally grow well in a humid environment. Some tolerate drier conditions than others, but most prefer higher levels.
Because it’s low-growing vegetation, soil moisture plays a big part in your lawn’s local humidity. Even in dry climates, turf kept in moist soil and out of direct sunlight usually won’t suffer humidity issues.
Grass grows best in slightly acidic soil with a pH between 5.0 (acidic) and 7.0 (neutral). Higher or lower levels can keep grass roots from absorbing the nutrients they need, which weakens the turf and reduces resiliency and tolerance to drought.
It’s a good idea to use an inexpensive test to find out your soil’s pH. Each species has a specific pH range it prefers. If your readings veer wildly from the correct range, you can add amendments to adjust the pH higher or lower.
Your lawn is a heavy feeder and needs a significant level of macronutrients to grow at the brisk rate we want for our lawns – often more than natural soil can provide. Supplying these elements at the right time keeps grass production humming.
The three most-needed macronutients are nitrogen, phosphorus, and potassium. Nitrogen is the primary element for building those beautiful grass blades, and it’s consumed in relatively high quantities. Unfortunately, nitrogen can leech from the soil with watering, so it’s also the element that requires the most supplementation.
Apply as sparingly as the label suggests. Feeding your lawn too much nitrogen can stimulate a profusion of tender, weak growth. On the other hand, a lack of nitrogen turns the grass pale or yellow, a condition called chlorosis.
How To Maximize Grass Growth
Though your grass never really stops growing, it will grow healthier and faster with good maintenance.
Considering that your grass grows all night, you might wonder if it matters what time you water. There isn’t a cut and dried answer, but here are some tips:
- Your lawn grows best when the top six to eight inches of soil are moist. This translates to about 1 to 1.5 inches of water, the weekly amount recommended for most growing lawns.
Pro Tip: You can determine how long it takes for your sprinkler system to deliver an inch of water by putting out small, shallow tins and timing it.
- After a night’s growth, your grass is fresh and ready for more nourishment. You can set your sprinkler for as early as one hour before sunrise without overwhelming the turf or encouraging fungal issues.
- If you want to water during the day, morning is the best time. You want the water to evaporate during the daytime – grass left wet overnight is vulnerable to mold, fungus, or even root rot.
- If you water later in the day, do it early enough that the grass has time to dry before nightfall.
Even if the pH and nutrient level are correct, grass won’t grow well if the soil is impermeable or lacks enough structure to retain moisture. Organic material is the solution to either condition.
Aeration can help you amend the soil without disrupting the turf too much, and it’s one of the best things you can do to improve soil quality, especially if you have compacted soil. It’s a valuable maintenance chore that only needs to be done once or twice a year – spring or fall – or before sowing seed.
Aeration is done with a machine that pulls cylindrical pellets from the soil, leaving small, open divots in the turf. After aerating, you can rake compost, sand, or other suitable material into the holes to improve the soil’s texture.
Besides good soil and careful watering, proper fertilization is probably the biggest factor in turbo-charging a lawn’s growth. Grass can deplete soil of its nutrients, but timely supplementation can keep your turf healthy and full.
It’s smart to get the soil tested before fertilizing. Either a home test kit or a mailed sample to your local agricultural service can do the job. If your soil shows a deficiency, use a fertilizer with an extra amount of the missing ingredient. You can see dramatic improvements in your lawn when you give hungry grass a nutrient it was missing.
The biggest danger with fertilization is overdosing. Too much fertilizer can shock the plant and burn its roots, turning the blade tips or even the whole leaf brown. Use the highest dilution recommended and watch your grass’s reaction.
Slow-release formulas can be effective but harder to gauge than single applications.
Pro Tip: Though inorganic blends can be used safely and with great results, it’s much easier to overfertilize with concentrated synthetics than when applying organic fertilizer.