Indoor Plants: Air Quality and Growing Conditions

2. OBJECTIVESThe student will be able to… • Describe howplants can“clean” indoorair.

3. OBJECTIVESThe student will be able to… • List ways the indoor environment differs from the outdoor environment in terms of plant growing conditions. • List four of the six indoor environmental conditions affecting interior plant growth. • Describe what to look for before purchasingan indoor plant. • List the points for which one should “inspect” indoor plants on a biweekly basis. • Describe the differences in how renewalpruning, thinning, and pinching are done.

4. INTRODUCTION • Almost every home now displays at least a few indoor plants. • Hanging baskets, freestanding plants, window sill pots. • Many people enjoy being surrounded by plantsin the home, at work, or where they shop, or dine. • Indoor plants link the outdoor world of nature and the indoor domain of people in a mutual living space. • Many commercial buildings have atriums, skylights, and lighting to accommodate plant requirements. • Commercial interiorscaping or interior landscaping isa multi-billion-dollar industry with a technological base.

5. INTRODUCTION • Scientific advancements have made houseplant growing more successful for the average person. • New cultivars have been selected or generated fromtissue culture mutations—some never commercially produced or even cultivated until relatively recently. • Much more durable, and better able to survive—even thrive—in less light & humidity than the original species. • Also selected for pest resistance, though this is amore elusive quality than environmental adaptability. • Much research has focused on developing new, more dependable flowering plants, with longer lasting flowersin a wider range of colors.

6. PLANTS - CLEANERS OF INDOOR POLLUTANTS • Research over the past two decades has shownthat plants improve indoor air quality. • During the 1970s, self-contained ventilation systemsthat recirculated the air became standard. • Most big commercial buildings are still designed this way. • Pollutants can accumulate to levels that make the air inside these buildings more polluted, in some ways, than the outside air of a large industrial city. • Recirculating air has led to a collection of illnesses referred to as “sick-building syndrome.” • Physical symptoms such as respiratory infections\difficulties, headaches, skin or eye irritations, nervous system disorders, and even psychological disturbances.

7. PLANTS - CLEANERS OF INDOOR POLLUTANTS • Common chemicals identified as indoor pollutants: • Carbon monoxide, nitrous oxide, benzene, formaldehyde, and trichloroethylene. • Acetone, ammonia, toluene, and xylene. • Carbon dioxide, nitrous oxide, benzene.

8. PLANTS - CLEANERS OF INDOOR POLLUTANTS • The obvious solution, better ventilation, is ill advised in cities where exterior pollution levels are high. • Plants are effective in “scrubbing” the air. • NASA research is the main source of informationon the air-cleaning abilities of various plants. • Almost every plant tested reduced pollutants, withvariation in which plant was most effective onwhich pollutant. • In general, plants that can live in low light andhave large leaves remove pollutants best. • Soil is found to play a role in removing pollutants. • Soil microorganisms play a particularly important part.

9. PLANTS - CLEANERS OF INDOOR POLLUTANTS Potted plants, when combined with activated carbon filters and a fan were more effective than just the plants alone. The carbon absorbed pollutants,and the roots grew into the carbon, degrading the chemicals there. Discovered in the research wasthat plants & soils continuously exposed to air containing toxic chemicals actually improve theirability to clean air, over time. See the entire tableon textbook page 273.

10. THE INDOOR ENVIRONMENT • A plant must adapt to many environmental conditions to live indoors. • Light, temperature, humidity, water quality, containerization, and air circulation. • Plants will always be at a disadvantage indoors because human comfort will always be the primary consideration.

11. THE INDOOR ENVIRONMENTLight • Light intensities comfortable for living and working are insufficient for many species of plants. • If plants do not receive sufficient light to manufacturecarbohydrate required for respiration, they eventually die.

12. THE INDOOR ENVIRONMENTTemperature • Outdoors, cooler night temperatures reduce the rate of respiration & prevent rapid depletion of stored carbohydrate reserves. • Plants grown indoors are often not exposed to cool night temperatures, and their carbohydrate reserves are used more quickly. • The plants have little or none to use for new growth.

13. THE INDOOR ENVIRONMENTInsufficient Humidity • Insufficient humidity causes tropical plants to lose water more rapidly by transpiration than in their native environment. • Often water is transpired faster than it can be replaced. • Leaf tips turn brown, and plants develop other symptoms indicative of insufficient humidity.

14. THE INDOOR ENVIRONMENT Water Quality • Rainwater has relatively few impurities & generally, a neutral pH—neither acid nor alkaline reaction. • Tap water, depending on source & prior treatment, may contain numerous chemicals such as chlorine, sodium, or fluoride. • It may be acidic or basic, which, over time, will affectthe availability of nutrients from the growing medium.

15. THE INDOOR ENVIRONMENTContainerization • Nutrients and water available to the plant arelimited by the small amount of medium in the pot. • Must be more carefully regulated than for plants outdoors. • Soil that is loose and drains quickly outdoorsmay pack down and drain slowly in a pot. • Garden soil is often not suitable for houseplantuse unless it is mixed with other materials.

16. THE INDOOR ENVIRONMENTAir Circulation • Outdoors, air movement is fairly constant dueto changing temperatures and natural winds. • But indoor air can be relatively stagnant during thewinter months when windows remain closed. • Fresh air is likely to come through an outsidedoors, possibly 40 deg. F colder than room temperature. • Plants in the direct path of doors can often sufferundiagnosed illnesses from rapid temperature changes.

17. PURCHASING INDOOR PLANTS The way a plant looks in the storeis not necessarily how it will look after 2 or 3 months at home. Regular indoor light intensity is often not strong enough to cause new buds to set After present buds are exhausted, the plant is unlikely to bloom. See the entire table on textbook page 275. • There are bargains & lemons among indoor plants. • As with any other purchase, it pays to shop around.

18. PURCHASING INDOOR PLANTS • A well-grown houseplant will be compact and have richly colored foliage, strong new growth, and a full crop of leaves. • The stem should easily support the weight of the top and have no weak or discolored areas, especially at the base. • Check growing tips, leaf undersides, and potting mediumfor hiding pests or signs of their damage. • Plant prices vary according to where it is purchased, the species, cultivar, etc. • Mass-merchandising outlets normally have lowest prices, florists the highest & local greenhouses, in between. • Mass-merchandising outlets usually have least selection, and plants displayed for long periods may be in poor condition.

19. PURCHASING INDOOR PLANTS • Price charged for a plant is often a reflection ofease of propagation & time needed to grow to selling size. • Wandering Jew and coleus, for example, propagatevery easily from cuttings and grow rapidly. • Kentia palms are grown from seed, and take anaverage of 8 to 12 months just to germinate. • Wrap a newly purchased plant in paper, or enclosein a paper bag—folding leaves upward—before taking it outdoors, to protect against the sudden temperature drop.

20. ACCLIMATIZATION AND CONDITIONING • Plant shock is common in new houseplants. • Sudden change to lower light and humidity disturbsthe plant metabolism and temporarily halts growth. • Leaf drop may occur, and some plants even may die. • Properly grown houseplants are conditionedor acclimated prior to sale. • Light & humidity are lowered gradually, with watering & fertilization at levels commonly found in indoor conditions. • Plants not acclimated appear extremely lush and bright green, with much new growth, and dense,soft or succulent foliage. • Healthy, vigorous plants that would to grow well in a greenhouse, but not adjust well to indoor conditions.

21. ACCLIMATIZATION AND CONDITIONING • To acclimate a tropical plant not conditionedbefore sale: • Give the plant the maximum light & humidity available. • Keep the soil moist. • Gradually move further from the light & decrease humidity and water to recommended range over several months. • After acclimatization, the plant should grow slowly but satisfactorily provided the correct light level and other requirements are met.

22. MAINTENANCE ACTIVITIESInspection • Inspection of houseplants should take place every1 to 2 weeks & consist of a general search of the plant for any signs of poor health. • New growth should be scrutinized carefully forsigns of pests such as spider mites. • More mature leaves should be examined both above and underneath, where insects frequently hide. • Leaf axils are a favored spot of concealment for pests. • If young growth is spindly or many lower leaves are beginning to yellow, growing conditions should be altered to remedy the problem.

23. MAINTENANCE ACTIVITIES Cleaning • Outdoors, rainfall regularly washes plant leaves. • It removes dust & dirt that block light and decrease photosynthesis. • Indoors, most water is applied directly to the soil. • So leaves never are cleansed. • Periodic washing/dusting is a substitute for natural cleansing by rainfall & should be done wheneverthe leaves show an appreciable amount of dust. • It also helps remove insects & lessen pest problems. • Small plants are perhaps most easily cleaned bythe spray nozzle found on most kitchen sinks. • A shower is very useful for large-specimen plants.

24. MAINTENANCE ACTIVITIES Cleaning • For particularly stubborn residue, leaves can be sponge cleaned with a drop or two of detergentin a bowl of water. • The plant should be rinsed thoroughly afterward. • Many indoor gardeners find carrying large plantsto the shower every month is inconvenient. • A damp cloth or sponge is satisfactory, providedthe leaves are smooth and not easily damaged. • Especially where water has an appreciable mineral content. • Dusting with a very soft duster, such as a featheror lamb’s wool duster, is another way of cleaninglarge-leaved plants.

25. MAINTENANCE ACTIVITIESLeaf Shines • Many commercial plant shines or “leaf cleaners”are available in sprays, fiber-tipped applicators,and foil-encased towelettes. • All claim to improve the appearance of foliage and enhance the looks of plants. • Most garden books contend they are bad for plant health, because they cause “pore” clogging. • Plant “pores” (stomata) are not like human pores anddo not respond in the same manner to clogging • Most stomata are on leaf undersurfaces where leaf shine is not applied, and the majority will not be affected.

26. MAINTENANCE ACTIVITIESLeaf Shines • While most plant shines and leaf cleaners will not harm plants, a few will, especially young foliage. • Attributable most often to an aerosol propellant. • Nor are leaf shines or cleaners necessarily thebest way to clean plant leaves. • Some leave an artificial-looking gloss and an oily residue that attracts dust, whereas others leave no residue and only a slight shine. • Chemical makeup varies greatly among the brands. • Homemade leaf shines such as milk or salad oil were commonly used in the past. • Salad oil is not suggested due to the resulting greasy film. • Milk is safe and relatively inexpensive.

27. MAINTENANCE ACTIVITIESLeaf Shines • The hair-covered leaves of tropicals can be cleaned with a spray of water or dusted with a soft brush. • Leaf shines should not be used, nor hand wiping.

28. MAINTENANCE ACTIVITIESLeaf Shines Water over 10 deg F. cooler than room air temperature will cause yellow splotching wherever it touches the leaves. The resulting discoloration is caused from destruction of leaf chlorophyll, and is permanent. Figure 16-23 Spotting of Africanviolet leaves caused by cold water. • When rinsing the hairy-leaved members of the African violet family, use room temperature water. • Gesneriads are very sensitive to temperature change.

29. MAINTENANCE ACTIVITIESLeaf Shines The scales are decorative, but their function is highly practical. The cells are for absorbing water directly through the leaves. Figure 15-1 White bands of water-absorbingscales on Aechmea bromeliad. Rick Smith photo. • Some indoor tropicals have a natural filmlike coating that should not be rubbed or covered with leaf shine. • The foliage of many bromeliad species is coveredwith flaky silverish scales.

30. MAINTENANCE ACTIVITIESLeaf Shines • Cacti and succulents frequently have a waxy cuticle that rubs off easily with the fingers. • An insulation layer against moisture loss & adaptation factor that helps them survive in arid environments. • As a general rule, leaf polishes or cleansers should notbe used on cacti and succulents.

31. MAINTENANCE ACTIVITIES Turning • Plants indoors normally receive their light from a nearby window—leaves facing the light receive more solar energy, causing the plants to develop more in the direction of the light. • To prevent plants from becoming lopsided, turn aquarter-turn every few weeks so different sectionsof foliage face the light.

32. MAINTENANCE ACTIVITIESPruning • Indoor plant pruning is often neglected, resultingin many poor-looking houseplants. • Pruning causes branching &new growth, producing a fuller, more attractive plant. • It removes dead, insect-infested, or diseased plantparts to halt the spread of the organisms.

33. MAINTENANCE ACTIVITIESPruning - Pinching   a. b. Figure 15-2(a) Pinching a coleus. (b) One month later after branching has occurred.Drawing by Bethany Layport. • Pinching consists of breaking off up to about 3” of the growing tips—the most commonly practicedform of pruning for indoor plants.

34. MAINTENANCE ACTIVITIESPruning - Pinching  • Plant meristems produce a plant hormone called auxin which inhibits growth of buds lower on the stem and prevents branching. • This hormonal effect is termed apical dominance. • Indicating the top bud (apical meristem) “dominates”the growth of the buds below it. • Auxin concentration decreases as it moves down. • The lowest buds sometimes overcome dormancyand grow into shoots. • Auxin manufacturing rates & movement vary. • Why some plants branch naturally, when others do not.

35. MAINTENANCE ACTIVITIESPruning - Pinching   a. b. Figure 15-2(a) Pinching a coleus. (b) One month later after branching has occurred.Drawing by Bethany Layport. • When a growing tip is removed, it is nearly always the buds nearest the tip that begin growing. • Pinching removes the auxin source on plants thatwill not branch of their own accord.

36. MAINTENANCE ACTIVITIESPruning - Pinching   a. b. Figure 15-2(a) Pinching a coleus. (b) One month later after branching has occurred.Drawing by Bethany Layport. • While sometimes only one will grow, usually two to three appear, producing several new leafy shoots. • They soon begin auxin manufacture, keeping budsbelow dormant, and the cycle continues

37. MAINTENANCE ACTIVITIESPruning - Pinching  • Pinching must be done regularly on some species to promote constant branching & develop a full plant. • Leafy, vining houseplants most often require regular pinching to prevent a stringy appearance. • Ideally pinched frequently to develop a large numberof cascading stems.

38. MAINTENANCE ACTIVITIESPruning - Pinching  The most commonvining and upright-growing houseplantsrequiring frequentpinching are listed. See the table on page 278 of your textbook.

39. MAINTENANCE ACTIVITIESPruning - Renewal Pruning Figure 15-3 Stages in renewal pruning. Drawing by Bethany Layport. • Renewal pruning—removing all or nearly all foliage, leaving only 1- to 2” stems—is used to rejuvenate a plant that has become unattractive & bare-stemmed. • In several weeks new growth begins from leafless stubs.

40. MAINTENANCE ACTIVITIESPruning - Renewal Pruning • Renewal pruning is a drastic measure, used onlyif the plant is basically healthy, with a strong root system, and stored carbohydrate reserves. • With regular pinching and improved growing conditions, the plant will become attractive again in a few months.

41. MAINTENANCE ACTIVITIESPruning - Renewal Pruning • For plants in a severely weakened condition… • The source of the problem should be corrected, to encourage healthy growth. • Often sufficient to break the dormancy of lower buds. • After the plant is partially refoliated, the remaining unattractive portions can be cut back. • Leaving some foliage prevents further carbohydrate depletion.

42. MAINTENANCE ACTIVITIESPruning - Thinning • Many houseplants such as spider plants grow in a form called a rosette & produce new foliage from a short section of stem at soil level called the crown. • Others, such as most ferns, send up new leaves from an underground rhizome system. • Botanically speaking they have no “stems” above ground. • Only leaf petioles. • Each new shoot is a single leaf, and dormant buds are found at the crown at or just below soil level. • It should be cut off at the base to promote new growth from the crown, as pinching a leaf back will nevercause branching.

43. MAINTENANCE ACTIVITIESPruning - Plants that Seldom Require Pruning A moderate percentage of houseplants seldom require any pruning except removal of dead leaves. Pinching or renewal pruning these plants often destroys their form, creating an unnatural appearance.

44. MAINTENANCE ACTIVITIESPruning - Flowering Houseplants • Flowering houseplants follow the basic rules for pruning that apply to other houseplants. • For many, the flowering period can be lengthened by removing flower heads & seed pods as blooms fade. • Exceptions to this practice are plants in which the fruitis an ornamental feature, such as Christmas cherry.

45. MAINTENANCE ACTIVITIESPruning - Disease and Insect Control • Pruning for the control of diseases and insects isnot a common because in most cases, the entire plant is infected before the problem is discovered. • Pruning is valuable in dealing with houseplant foliage diseases, because chemical cures rarely are available. • When pruning for this purpose, cut back all diseasedportions to healthy areas. • Clipping of browned leaf tips is commonly usedto improve the appearance of houseplants suchas dracaenas and palms. • Temporarily effective; leaf tips usually brown againwithin weeks.

46. MAINTENANCE ACTIVITIES Transplanting/Repotting • Transplanting (repotting) is a routine part of indoor plant maintenance, performed repeatedly from the seedling or cutting stage through maturity. • Primarily done to provide crowded roots with additional potting medium from which to absorb water and nutrients. • Less often as a general tonic or cure for an undiagnosed ailment suspected of being caused by roots or potting medium. • Most people repot more often than necessary. • Switching to bigger pots when frequent fertilizationwould have been sufficient. • Although unnecessary, repotting seldom is harmful, and it involves a considerable amount of extra work.

47. MAINTENANCE ACTIVITIES Transplanting/Repotting • Several factors must be evaluated to determineif a plant should be moved to a larger container: • Does the plant look top-heavy in its pot & tip over easily? • A plant with a large mass of foliage will grow best if given an adequate volume of potting medium to support that top growth. • Keeping it in an undersized pot will stunt its growth. • Does the plant require frequent watering to keep the soil moist, and does it wilt within a few days of watering? • Overcrowded roots extract available water and nutrients very quickly, necessitating more frequent watering and fertilization. • Is the health of the plant declining with no change in care or growing location? • Some houseplant media pack and crust on the surface after a period of months or years and repotting may be advisable.

48. MAINTENANCE ACTIVITIES Transplanting/Repotting • Some gardeners use the presence of roots growing from the drainage hole or circling the root ball as an indicator for repotting—not always reliable. • Roots grow most vigorously in areas that hold both moisture and air. • Soil near drainage holes, and around the inside surface of unglazed clay pots most ideally provides these conditions. • If large numbers of roots have grown in circles, repottingis justified, as the bulk of the root system is not in contact with the potting medium.

49. MAINTENANCE ACTIVITIES Transplanting/Repotting • Season is not important for repotting indoor plants. • Most are performed in spring or summer, as increased vigor due to increased light & humidity makes plants outgrow their pots quickly during these periods. • Blooming plants should be transplanted when not flowering, as it is common for a plant to drop buds and flowers prematurely when roots are disturbed. • Repotting blooming plants immediately after floweringprovides room for new root growth and, consequently, better foliage growth before the next flowering period.

50. MAINTENANCE ACTIVITIES Transplanting/Repotting - Unpotting Only in very difficult cases should a plantbe loosened by pulling on the stems. Root or stem damage is likely to result. Figure 15-4 Knocking a spider plantout of its pot. Photo by Rick Smith. Plants in 8” or smaller-sized containers can usually be unpotted by a technique known as knocking out Medium should be moist to keep from falling away from the roots. Support the top of the soil & plant stem, turn pot upside down & lightly tap the edge on a counter or table. The soil and roots should slide out intact.