Air: The Invisible Ingredient for Successful Growing

, written by Bob Flowerdew gb flag


One of the most important factors for success with plants is the air. Yet, as it is not visible, it often goes unnoticed and is not considered so important. However it takes part in several different interactions with plants, and to understand them we need to examine what air is made of. The constituents that concern us are the carbon dioxide (which makes up a minute percentage), oxygen which is about a fifth, four fifths nitrogen and water vapor (or humidity). Each has a different role and each may affect growth.

Plants Need Carbon Dioxide

Carbon dioxide is converted by photosynthesis in most green parts (not just the leaves) into various organic chemicals which the plants then use for growth, and to store energy. Carbon is the key ingredient of all living matter and most of this is obtained from the air, although some is also taken up from the soil.

However as carbon dioxide is in such a small proportion, it can be rapidly removed from the air if this is not moving. In still air and bright sun a field of corn can use all available carbon dioxide within half an hour. Now, although there is a surplus of carbon dioxide in the whole system, this rapid removal down near ground level means that replenishment from elsewhere is necessary if plants are to keep growing. Fortunately almost all life in the soil is continually giving off carbon dioxide and this emerges underneath the leaves (where it is to some extent trapped) and is thus available to the plant.

Roots Need Air

Indeed, it is little understood how roots and all non-green parts of plants (as well most micro-organisms) breathe like us, taking in oxygen and giving out carbon dioxide. They are burning carbohydrates with oxygen for the energy to grow and perform other functions.

Beans take in carbon dioxide which is then used for growth by the roots
Beans take in carbon dioxide which is then used for growth by the roots

Because of this, soil needs to be aerated. A quick way to kill most plants is to waterlog the soil. Their roots drown as they can get no oxygen. Indeed the main benefit of improving drainage is to improve the aeration. Digging and incorporating gritty, fibrous or coarse textured materials may help but worms are the main aid as their tunnels provide easy ingress for air, down to two meters in some soils. (Also when heavy rain falls their tunnels fill, expelling stale air and then as the water drops down or is absorbed fresh air is sucked in.)

The Effect of Wind

Wind is one of the other more obvious effects of air and its effects can be good or bad. In many cases it causes direct damage, rocking plants and loosening roots, blowing off leaves and even breaking branches. It may also pick up small objects to batter the plants causing bruising.

Another major drawback of wind is its cooling effect. Although this may be welcome in hot weather, generally, in temperate climes, it acts to reduce the effective temperature and so slows growth. But even a wind as of just a few miles per hour causes most plants to reduce transpiration and growth. Strong cold dry winds are worst as they suck moisture from plants searing leaves and causing wind burn destroying leaves and flowers.

On the other hand in stagnant air, such as enclosed gardens with tall hedges or surrounding trees, the lack of air flow reduces growth, the likely high humidity causes an increase in disease (nothing promotes mildew, rusts and fungal diseases so effectively as plants in damp air with dry roots). Because the air is stagnant and not moving them then plants develop weak stems and become spindly and drawn, and probably etiolated (leggy, yellowish growth) as well if light levels are also lowered.

Increasing Throughput of Air

Where a garden is at the bottom of a slope then cold air, acting much like water, can pool and form a frost pocket. Enclosed gardens on slopes should have a gate, hole, gap, or some place that cold air can pour out. Never close off all openings on to a ditch or stream for this reason- it will be at a low point and is essential for removing cold air.

Plants in a greenhouse
Plants growing in a greenhouse need ventilation

Under cover fresh air becomes even more important. Although plants do not like being in draughts they loathe stagnant air and all cover should be given maximum ventilation. Most greenhouses and tunnels are insufficiently well ventilated! One reason is that we like to keep them shut up for the warmth. Commercial growers do likewise but then supply carbon dioxide from compressed bottles. You can simply put fermenting liquids (sugar and yeast in water will do) under the staging to supply carbon dioxide in a similar way. (Or keep pets there – permaculture systems sometimes link a hen house with a greenhouse for this reason and for the added warmth.) Regular ventilation will still be necessary to prevent disease.

Finally, researchers using artificial light to grow plants found that over-crowding plants reduced their growth more from the hindrance to air movement than from the shading. So do remember to keep your plants well spaced.

By Bob Flowerdew.

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Show Comments


"This reference to growing under lights hindering air movement was very interesting. I am going out right now and move seedlings further apart!"
Pat Roloff on Friday 8 April 2011
"thats why my leek seedlings were all leggy!!"
di green on Saturday 9 April 2011
"Di, you'll find more information about what's going wrong with your leek seedlings in the following article by Barbara Pleasant about onions which are similar: (particularly some of the comments at the end of the article)"
Jeremy Dore on Saturday 9 April 2011
"I just love this web site. So informative. Now my question is, how do I move my seedlings from a small indoor greenhouse that I got at Walmart, to a 6' X 12' greenhouse we just put up this weekend outside by my garden? How do I regulate the temp from day to night? My little veggies are now in 3" pots and looking quite nice. I don't want to burn them or freeze them."
Faith on Sunday 10 April 2011
"Faith, if there is not much difference in temperature between the two greenhouses you can just go ahead and move them. Otherwise, gradually introduce them by taking them to the new greenhouse for a few hours and then back to the smaller one for a few days. To regulate the temperature in the new greenhouse you need to open the door and air vents during hot days and close them before temperatures drop at night. Bayliss greenhouse vents can help do this automatically, although you'll still need to open the door on very hot days (e.g. If you get a late frost forecast it's worth bringing them indoors overnight."
Jeremy Dore on Sunday 10 April 2011
"thanks- I read the article before and found it really interesting and useful - but never related it to leeks!!"
di green on Sunday 10 April 2011
"I knew about good space between my growing plants in my green house. But providing needed carbon dioxide was something I didn't know. I love your site for these wonderful tips and information. Out to the green house I go with sugar and yeast!"
Pamela Jessup on Sunday 10 April 2011
"I'd like more info re chickens and greenhouses and or hoop houses. I just found 3 eggs from my free range chickens in my greenhouse yesterday so they must like it in there. What are the benefits/downsides/cautions....... "
Linda W on Friday 15 April 2011
"You are so awesome! I don't believe I have read something like that before. So good to find someone with some genuine thoughts on this issue. Really.. thank you for starting this up. This website is one thing that's needed on the web, someone with a little originality!"
Marquis on Wednesday 14 August 2013
"It's impressive that you are getting ideas from this article as well as from our argument made at this time."
Mcclendon on Monday 19 August 2013

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