Handbook for a Sustainable Greenhouse

Julie Baumgart

Capstone 499

Handbook for a Sustainable Greenhouse

Dr. Robin Richardson

Fall 2010

Sustainable methods of treating small outbreaks of mealy bugs and scale insects include dipping a brush into methylated spirits such as eucalyptus oil. Another method of treatment is to use an organic washing liquid with lukewarm water to clean the affected areas on citrus plants for example. This treatment shouldn’t be used with sensitive plants or done in direct sunlight because of sensitivity issues. There are ways to reduce pest outbreaks such as making sure plants are examined and cleaned before entering a greenhouse. It may be helpful to quarantine new plants for several days so that certain types of pests can mature and be found more easily in order to treat (Tampion, 1999). Clear sticky tape such as Sellotape can be used to find and remove insects from leaves and stems. Plants can be affected in different ways by pest infestations. Pipevines for example are rarely infested with aphids whereas the family Asclepiadaceae can become heavily infested by aphids (Tampion, 1999).

Pests

Aphids reach maturity in about 7-10 days and can produce 40-60 live offspring. Aphids live in colonies and their infestation can lead to depletion of sap in plants because the sap is what they feed on to grow and mature. The method of infestation of aphids is that they attack the terminal growth areas of the plant and from there they suck the sap and water from the plant which leads the plant to wilt and turn yellow. Feeding aphids will not critically harm healthy and hearty trees and shrubs; it just makes the plant less aesthetically pleasing. There are plants that are more sensitive to the saliva of aphids and the fruit and/or flower production can be diminished. Aphids produce honeydew which fungus can grow on. The honeydew may accumulate on the leaves and branches and that can make the affected areas turn black. This is the point in which the infestation is obvious. Ants and other insects may be attracted to the sticky deposits which just increases the infestation. A way to control an infestation is to practice early detection and examine plants (Townsend, 2010).

Mealy bugs are insects that are seen with “fluffy white wool” which is actually a waxy material when scraped. Females are the most common because the males live shorter lives and their wings are rarely seen because their wings are so small. The females live just long enough to reproduce and lay eggs. The most common area of a plant to feed is where the leaf attaches to the stem. The infestation most seriously damages passion flowers (Tampion, 1999).

Red spider mites are red in color but the color only appears by inactive hibernating mites. The mite is actually green with dark spots. They are small and magnification may be needed to seen. A fine silky thread is left on the leaves as well as leaf joints and that causes the leaves to wilt. Mites have a rapid life cycle but increased temperature and dry conditions may speed up the life cycle even more. Females can reach maturity in about a week and can lay over 100 eggs. Infestation can be confirmed by using clear sticky tape or by using magnification (Tampion, 1999).

There are many species of scale insects but they are usually assorted into hard and soft type categories. They are commonly found on citrus plants but can also be found on a variety of other plants. They appear brown in color and have small domed scales on the leaves. Scales suck the sap from the vascular tissues of the plants and then they secrete honeydew which makes a thick coat of dark fungus which reduces the plants ability for photosynthesis to happen. A sustainable approach to managing small infestations is to use a brush dipped in methylated spirits such as eucalyptus oil. Another approach is to dilute washing liquid and use a soft sponge to wash off both the scales as well as the fungus (Tampion, 1999).

Thrips are small, black, and have elongated bodies. They are hard to identify from one species to another. Thrips travel easily from one place to another when they are disturbed. They are mostly found in flowers which allow them to go undetected. The females lay their ova under the surface of leaves and then they become colorless which is then followed by the development of a more yellow color as they mature. Thrips can be found on the underside of the leaves of plants. Infestations cause quite a bit of damage to sensitive plants especially if they accumulate over time. Leaves can become covered with silvery flecks and that can lead the plant to shrivel up and die. At maturity they fall to the ground where the adult then emerges. A sustainable approach to handling an infestation is to wash the leaves of plants such as the Asclepias species to remove the infestation. This treatment isn’t safe for some other plants. It takes quite awhile to control serious outbreaks because mature thrips continue to breed (Tampion, 1999).

Whiteflies are one of the most common pests found in a greenhouse. The adults are small in size but are clearly visible when disturbed. They are covered with a white waxy material. Adults lay small groups of ova which hatch into a stage which actively seeks out the veins of a leaf. They attach to feeding scales which grow and create sticky honeydew which encourages secondary mold to grow. They pupate on leaves, emerge as adults, and then move off to gather on other leaves that they are attracted to (Tampion, 1999).

Vine weevils are easily recognizable because their heads are elongated with a pointed snout. They are under an inch in size and dark brown in color. They feed on leaves by biting out small pieces. Potted plants have the serious problem. The larvae are white and the legless grubs eat the roots which then kills the plant entirely. It’s most difficult to treat the underground stage but biological controls such as small nematode worms can be used as a type of parasitoid to control the infestation of vine weevil grubs. The nematodes can be mixed with water and then poured onto the soil or combined into the compost (Tampion, 1999).

Millipedes and woodlice may accumulate in damp environments and they can damage developing plants. Treatment of infestation can include removal by hand or using a damp brick or a piece of wood as a lure (Tampion, 1999).

Slugs may accumulate in damp environments and are quite a nuisance. They can be removed by hand or may be lured into a covered trap baited with stale beer (Tampion, 1999).

A sustainable method of pest control is the use of organic neem oil. The oil from the bark and leaves of a neem tree are used as a natural pesticide and insect repellent. Neem oil used in a sustainable greenhouse should be used at about a 70% solution because direct treatment can harm hymenoptera which are vital in pollination of many plants and flowers. Neem oil used at 70% controls insects such as mites, whiteflies, scales, and aphids. It also controls some fungus growth on plants as well. The oil should be applied each week or two as needed. It can also be applied once every two weeks as a preventative method. For best results, two tablespoons of 70% neem oil should be added per one gallon of water. Spraying both sides of leaves as well as stems is important (Bradtke, 2010). There is another “green” alternative to pest control is using products such as EcoSMART. It’s an organic pest controller that is made of organic plant oils and contains no pesticide residue. The active ingredients are clove oil, rosemary oil, peppermint oil, thyme oil, and 2-Phenethyl Propionate. It’s a widely effective with reducing populations of over 100 pests, many of which are listed above (EcoSMART, 2010).

Soil Cycles

Soil is made by the degradation and weathering rocks. Glacial movement created much of the soil throughout the Midwest. “The debris from rocks over which the glaciers passed was left as they receded. Glacial till, the material left in place by the glaciers is a mixture of various sizes of soil particles, gravel, rocks, and sometimes boulders of various sizes. Glacial outwash soils are mixtures as well, but often are stratified in layers.” The Midwest has mostly loess soils which were created by the wind. Fine soil particles are picked up from riverbeds by the wind. Riverbeds were created by retreating glaciers and the finer particles such as silts and clay blew farthest east (Fizzell, 2007). Figure 1 shows the much simpler soil cycle that exists in a greenhouse simply because there are less factors that can weather materials that are found in a greenhouse environment. Due to the enclosed environment, soil cannot be weathered as it would be in an outdoor environment. Photosynthesis can readily occur in a greenhouse with many windows and can be as effective as it would be outdoors. CO2 respiration is also not effected by an indoor greenhouse. Factors that wouldn’t be included are wind, rain, extreme heat or cold, or erosion due to recession of outwash.

Figure 1

Soils are categorized according to particle size. Sands have large particles and the grains are visible to the naked eye. Sandy soils are usually infertile because the soil is easily washed of nutrients by rains or irrigation. The particle size allows for the soil to be well drained. Sands are usually found in river valleys (Fizzell, 2007).

Silt soils contain small particles which are too small to be seen without magnification. Silt soils hold nutrients well, however, they are usually poorly drained which results in the soil becoming compacted under its own weight. If silts are managed properly, they can be a productive soil. For instance, the soils found in Salinas Valley California are large silts and the farmers have learned to manage the soils up in the hills and then grow their crop such as lettuce before the hills collapse (Fizzell, 2007).

Clay soil is the most productive type, although, they can be difficult if not managed properly. If they are worked in environments that are too wet or too dry, if they are kept too wet, or if they are walked on so that they become compacted, then the soil becomes unworkable. If they are properly handled then they are workable. Clay particles are microscopic and they have electrical charges which cause them to stick together and results in the formation of aggregates. Calcium promotes this formation to take place. Calcium should be tested before it’s added to the soil. With proper structure clay can hold large amounts of water inside the aggregates. Air is able to be let in if large spaces are present. Clays can be well drained and can provide plenty of water and nutrients to the plants (Fizzell, 2007).

Loam soils have the appropriate mixture of sand (20-80%), silt (40-60%), and clay (10-30%) which allows for the benefits of each kind of soil type to coexist (Fizzell, 2007).

Organic Matter

Organic matter is created from the breakdown of plants, leaves, peat moss, cottonseed meal, compost, and manure among other things. Organic matter that contains large particles open the soil so that air can get in which improves heavy soils. Particles of organic matter act as sponges which hold water and improve soils that are light and sandy. Soil microorganisms break down organic matter which results in nutrients being recycled. The microorganisms also help reinforce soil particles together which improves aggregation of clay soils. Plenty of organic matter is essential for healthy and productive soil (Fizzell, 2007). Figure 2 depicts the process of how dirt becomes “living” soil by the process of breakdown of organic matter and with the addition of microorganisms that aid in the benefici

Figure 2

Soil Chemistry

Soil provides most of the nutrient demands of plants and productive soils usually have enough of the elements in forms accessible to plants. Carbon, oxygen, and hydrogen come from air and water. The proper soil acidity and adequate air and water are essential for these elements to be obtainable. The key elements needed in larger amounts by plants are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Minor elements are those needed in smaller amounts and include iron, manganese, boron, zinc, copper, molybedenum, cobalt, and chlorine. Native soils are seldom deficient in minor elements. The minerals that make up loam soils typically provide adequate calcium, magnesium, and potassium as well. They are part of the chemical framework of the rocks from which these soils came. Garden soils usually lack the major elements of nitrogen, phosphorus, and potassium because they are used up by the majority of plants (Fizzell, 2007).

Nitrogen

Nitrogen is needed for the proteins that develop the tissues in plants. Air contains about 80 percent nitrogen but plants aren’t able use it in that form so soil organisms capture atmospheric nitrogen and convert it into forms that plants can use. The majority of the nitrogen in the soil is part of the organic matter. As the nitrogen decomposes, it is released, and recycled by the plants and soil organisms. It doesn’t matter if organic nitrogen, inorganic nitrogen, or natural nitrogen is added to soil because organisms will convert it either way into a form useable by plants (Fizzell, 2007). Figure 3 shows the nitrogen cycle that takes place in soil and how it is processed from the air and into the soil.

Figure 3

Phosphorus

Elemental phosphorus is a white material that is quite poisonous and flammable. Of course, plants cannot use it in that form. Phosphorus combines with hydrogen and oxygen in the soil, creating usable forms depending on the soil pH. Rock phosphate has accumulated over many years in soils that have been formed. Much of the phosphorus is held firmly in the soil and plants can’t absorb it. Plants need phosphorus for healthy roots, flowers, and fruits (Fizzell, 2007).

Potassium

Potassium strengthens plants and encourages in the development of flowers and fruits. Clays contain potassium, magnesium, aluminum, and iron silicates. Most of the potassium in the soil is held tightly so plants aren’t able to absorb it. It is recommended to add potassium to the soil before it is tilled. When soluble potassium is applied in solution it is more readily accessible to plant roots (Fizzell, 2007).

Soil alkalinity/ Acidity-pH

Soil pH is a measure of the acidity or alkalinity. Soil is neutral at a pH of 7.0. Above 7.0, the soil is alkaline. Below 7.0, the soil is acidic. Most garden plants prefer a pH of 6.0 to 7.0. Soils with a high pH are quite difficult to change (Fizzell, 2007).

Gardening Soils

Planters filled with garden soil are poorly drained because they don’t have the deep, natural soil profile through which the water can seep into, which results in the water becoming stagnant and the development of an anaerobic environment. A good soil mix for general use consists of 1/3 garden soil, 1/3 course organic matter such as shredded leaves, compost, or peat moss, and 1/3 course sand. Containers should have drainage holes (Fizzell, 2007).

Soil

Soil contains billions of bacteria and fungi which constitutes soil as a living system. Soil results from five factors which are listed below.

1. Parent material
2. Climate
3. Biotic factors (plants, animals, bacteria, fungi)
4. Topography
5. Time

Animals, bacteria, and fungi decompose organic matter and aerate the soil to allow for water to pass through. Invertebrates in the soil such as millipedes, centipedes, earthworms, mites, springtails, and grasshoppers consume organic matter and excrete out partially decomposed materials. Soil texture is determined by the ratio of different sized soil particles. Texture is somewhat inherited from parent material and results partly from the soil-forming process. Without space, oxygen, food, water, and activity of living organisms, soil development couldn’t be maintained. Earthworms burrow in soil and deposit aggregates which produce more space in heavy soils for aeration. They also improve soil environment for other organisms. Millipedes feed on surface matter and eat leaves that are partially decomposed by fungi. Snails and slugs posses a wide range of enzyme which allow cellulose and other plant polysaccharides to be hydrolyzed (Smith et. al., 2001)