potting soil

Materials used for growing mediums include: peat, coconut coir, wood products like bark and wood fiber, perlite, stone wool, soils/tufts, and recycled paper and cardboard.{{Cite journal |last=Jackson |first=Brian |date=November 2022 |title=Current and Future State of the Growing Media Industry |journal=Greenhouse Grower |issue=November, 2022 |pages=20–24 |url=https://woodsubstrates.cals.ncsu.edu/wp-content/uploads/sites/147/2023/01/82-popular-press.pdf |access-date=2024-06-17}} Other materials used include rice hulls, sand, vermiculite, and calcined clays.{{Cite web |title=Growing Media - Ornamental Production Ornamental Production |url=https://aggie-horticulture.tamu.edu/ornamental/greenhouse-management/growing-media/ |access-date=2022-11-11 |website=aggie-horticulture.tamu.edu}}

Typical potting mixes include one or more materials which retain moisture, one or more materials which aid in aeration and drainage, and fertilizer. Moisture-retaining materials and aerating materials can be combined in any ratio, depending on the particular needs of the plant. Soils are minimally used as growing media because they compact and lose pore space after repeated watering and can be too heavy for growing potted plants.Pleasant, Barbara. "The Complete Houseplant Survival Guide." Pages 314. Storey Publishing. {{ISBN|1-58017-569-4}} Mediums used for growing plants in pots typically are a mix of organic and inorganic ingredients.{{Cite book |last=Arteca |first=Richard N. |url=https://books.google.com/books?id=84XAAgAAQBAJ&pg=PA339 |title=Introduction to Horticultural Science |date=2014-02-14 |publisher=Cengage Learning |isbn=978-1-305-17780-2 |language=en}}

Good growing mediums have a number of properties including moisture and nutrient retention capacity, quick water infiltration, pore space for aeration (plants roots need oxygen), drainage for excess water, decompose slowly, and provide support for the plants growing in them. They also have an optimal range of pH, cation exchange properties, and lack substance that are toxic to plants These are also dependent on the type of plant grown since there is wide variation in moisture and nutrient needs among different plants.

This part is usually made up of peat (usually with limestone to reduce acidity)Nissen, Dante. "The Indoor Plant Bible." Page 21. Barron’s. {{ISBN|0-7641-5769-8}} or coconut coir. It serves to absorb water and nutrients. Tree bark, mainly of pine, may also be used.

The use of peat is controversial since the harvesting of peat moss from peatlands (which includes unique habitats such as bogs and fens) can degrade these peatlands. Peatlands are home to a diverse range of plant and animal species. Peat also has a very slow accumulation rate, as little as 1mm per year, so they take a long time to regenerate. Peatlands are also carbon sinks, constituting 3% of the world's surface but storing up to 30% of the carbon sequestered in the soil.{{Cite news |date=2021-11-10 |title=Serious about climate change? Get serious about peat. |url=https://www.washingtonpost.com/world/2021/11/10/cop26-peat-carbon/ |access-date=2022-07-26 |newspaper=Washington Post |language=en}} The removal of the layer of {{CO2}} absorbing plants releases {{CO2}} into the atmosphere, contributing to climate change.[https://www.independent.co.uk/environment/green-living/gardeners-urged-to-stop-using-peat-based-compost-1918355.html Gardeners urged to stop using peat-based compost][https://www.washingtonpost.com/lifestyle/home/should-sustainable-gardeners-use-peat-moss/2017/05/09/1fc746f0-3118-11e7-9534-00e4656c22aa_story.html Peat moss: Good for plants but bad for the planet?]

As such, alternatives such as coconut coir are promoted by some organisations.[https://www.gardenersworld.com/plants/alternatives-to-peat/ Peat alternatives in the garden][https://www.rhs.org.uk/science/gardening-in-a-changing-world/peat-use-in-gardens/peat-alternatives Alternatives to peat]

Sand and grit may be used for drainage and aeration. Perlite and vermiculite improve both aeration and water retention.

All plants need essential plant nutrients to grow, so it is important to make sure there is a sufficient amount in the potting soil.{{cite web |last1=Leichty |first1=Corey |title=Does Potting Soil Need Fertilizer? |url=https://donotdisturbgardening.com/does-potting-soil-need-fertilizer/ |website=Do Not Disturb Gardening}} Some nutrients may be already present in the bulking ingredients.{{cite web |title=pottingmix |url=https://www.uvm.edu/vtvegandberry/factsheets/pottingmix.html |website=www.uvm.edu}} Peat contains 1% nitrogen that is almost never released. Limestone (for raising pH) contains mostly calcium (calcite), but can also contain magnesium (dolomitic). The latter is preferred as it supplies both elements. A typical proportion of limestone to peat is {{convert|8.5|lb/cuyd|kg/m3}}. Coir contains a high amount of electrolytes (salts). In fact, untreated coir contains too much sodium and potassium for plant growth, so it is washed and then buffered (partially replacing salts with other minerals, usually calcium and magnesium) to produce the growth medium. Vermiculite contains some calcium and magnesium, but more importantly it helps retain water and nutrients in the porous structure.

Nutrients not supplied by the bulk will need to be supplied by the fertilizer. In conventional mixes they may be slow-release formulae of synthetic fertilizers, while organic mixes will use organic source such as compost (e.g. leaf mold, bark compost or recycled mushroom compost). Overuse of fertilizers will, as with in normal soils, risk damaging the plant. For compost, the maximum recommended amount is 1 part compost to 1 part bulking material.

A soil test may be done to analyze the chemistry of a potting mix, despite the mix not necessarily being made of soil. As an approximation for indoor home planting, the mix is generally treated as greenhouse growth medium. The main method is a saturated media extract (SME), which tests the chemical contents of a water extract of the mix.{{cite web |title=Methods of Greenhouse Media Testing and How They Differ |url=https://ag.umass.edu/greenhouse-floriculture/fact-sheets/methods-of-greenhouse-media-testing-how-they-differ |website=Center for Agriculture, Food, and the Environment |language=en |date=6 March 2015}}

The growth medium should be adapted to each plant's (and growth stage's) preference for aeration, drainage, nutrition, and pH.[https://gardenranker.com/what-is-potting-soil/ What is Potting Soil?]

For seed starting, a "germination mix" is typically light-weight and suitable for starting small-seeded plants. A "seed starting" mix is suitable for larger seeded crops.{{Cite web|title=Guidelines for Starting Seeds Indoors, from Johnny's Research Team|url=https://www.johnnyseeds.com/growers-library/tools-supplies/seed-starting-transplanting-guidelines.html|access-date=2021-01-19|website=www.johnnyseeds.com}} Following early growth, most plants prefer a potting mix that is more well-draining.

Cacti and succulents require sharp drainage, thus requiring a much larger percentage of perlite or sand.Burne, Geoffrey. "Encyclopedia of Container Gardening." Page 22. Fog City Press. {{ISBN|978-1-877019-43-2}} Carnivorous plants, such as the Venus flytrap and the pitcher plant, prefer the nutrient-poor, acidic soils common to bogs and fens,{{cite web|url=http://www.philadelphiaweekly.com/articles/17273/a-e--dirty-buttons|title=Dirty Buttons - Arts and Culture - Philly Weekly|work=philadelphiaweekly.com|url-status=dead|archive-url=https://archive.today/20120907025516/http://www.philadelphiaweekly.com/articles/17273/a-e--dirty-buttons|archive-date=2012-09-07}} while water-based plants thrive in a heavier topsoil mix.{{cite journal|url=http://features.csmonitor.com/gardening/2008/06/18/creating-a-water-garden-in-a-tub/|title=Creating a water garden in a tub |journal=The Christian Science Monitor}}

Commercially available potting soil is sterilized, in order to avoid the spread of weeds and plant-borne diseases.{{cite web|url=http://www.tcpalm.com/lifestyle/columnists/carol-cloud-bailey-heat-potting-soil-to-prepare-it-for-replanting-ep-402745832-338716581.html|title=Carol Cloud Bailey: Heat potting soil to prepare it for replanting|author=Carol Cloud Bailey|work=TCP|archive-url=https://web.archive.org/web/20160530121331/http://www.tcpalm.com/lifestyle/columnists/carol-cloud-bailey-heat-potting-soil-to-prepare-it-for-replanting-ep-402745832-338716581.html|archive-date=2016-05-30|access-date=2016-05-30|url-status=live}}

As with garden soil, potting soil can attract insects. For example, the fungus gnat is often found around houseplants because it lays eggs in moist potting soil.{{cite web|url=http://www.azcentral.com/arizonarepublic/home/articles/0628martha0628.html|title=How to minimize dents in carpet from furniture|publisher=azcentral.com}}

Infections of Legionnaires' disease due to potting mix have been reported in Australia,{{cite journal|vauthors=Speers DJ, Tribe AE |title= Legionella longbeachae pneumonia associated with potting mix|journal=Med. J. Aust.|volume=161|issue=8|pages=509|date=October 1994|doi= 10.5694/j.1326-5377.1994.tb127576.x|pmid=7935133|s2cid= 28552691}} New Zealand,{{cite journal|vauthors=Kingston M, Padwell A |title=Fatal legionellosis from gardening|journal=N. Z. Med. J.|volume=107|issue=974|pages=111|date=March 1994|pmid=8127508}} the Netherlands,{{cite journal|last1=den Boer |first1=JW |last2=Yzerman |first2=EP |last3=Jansen |first3=R |last4=Bruin |first4=JP |last5=Verhoef |first5=LP |last6=Neve |first6=G |last7=van der Zwaluw |first7=K|title=Legionnaires' disease and gardening|journal=Clin. Microbiol. Infect.|volume=13|issue=1|pages=88–91|date=January 2007|pmid=17184293|doi=10.1111/j.1469-0691.2006.01562.x|doi-access=free }} the United States,{{cite journal|title=Legionnaires' disease associated with potting soil--California, Oregon, and Washington, May-June 2000|journal=Can. Commun. Dis. Rep.|volume=26|issue=22|pages=189–92|date=November 2000|pmid=11131692}} and Japan.{{cite web|url=https://www.cdc.gov/mmwr/preview/mmwrhtml/mm4934a1.htm|title=Legionnaires' Disease Associated with Potting Soil --- California, Oregon, and Washington, May--June 2000|publisher=Centers for Disease Control and Prevention}}

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