Horticulture: Unit 2

What are the Environmental Factors of Plant growth?

Light, Water, Growing Media, Essential Nutrients, Growth Hormones, etc.

Why is light important to plant growth?

Photosynthesis, affects how fast plants grow, what kind of growing plants do, and what shape plants grow in.

Factors to consider:

Intensity, distance from light source, quality, and duration.

Intensity:

brightness of the light

Light quality:

wavelength/color of light

Light duration:

length of light

What happens if a plant doesn’t get enough light?

The plants get leggy (stems get long and thing), chlorophyll production decreases, turns pale green/yellow/white, and leaves may drop.

What happens if a plant gets too much light?

Sunburn; leaves may appear scorched or bleached.

Low Light:

Tolerate 10-15 watts; thrive in North-facing windows/corner of room with little to no direct sunlight. Don’t need as much water.

Usually groundcover in forests.

Medium Light:

Tolerate 15-20 watts; thrive in East or West-facing windows and out of direct sunlight. Don’t need much water.

High Light:

Tolerate 20+ watts; thrive in South/south-west windows. Love brightly lit places, but soil drives faster so they need more frequent watering.

What to consider when choosing the right location for a plant?

Determine the light quality your area gets and choose a plant that would thrive in those conditions. May tolerate lower light than they do best in, they just won’t be as healthy.

Artificial Lighting:

Replacement for sunlight found when using LED or fluorescent bulbs. Controls the specifics about the type/length of light being received.

Light Spectrum:

Different plant systems use different light wavelengths.

What color lights are the best for plants?

Blue and Red light

What color light is the worst for plants?

Green, because the leaves have a green pigment already, therefore, they reflect the light (don’t absorb it).

Blue Light:

Produces healthy stems and establishes roots.

Red Light:

Produces longer stems ad increases the plant’s leaves, flowers, and fruits.

What are the three factors of leaves changing color in the fall?

Leaf pigments (chlorophyll), length of night, and the weather.

Carotenoids:

Produces orange, yellow, and brown pigments.

Ex: carrots, corn, daffodils, rutabagas, buttercups, and bananas

Anthocyanin:

Produces red pigments. Appears in the watery liquid of leaf cells.

Ex: cranberries, red apples, concord grapes, blueberries, cherries, strawberries, and plums

Chlorophyll:

Produces green pigments. Necessary for photosynthesis. Gives leaves green color during summer.

Which pigments are present during the growing season?

Chlorophyll and carotenoids

Which pigment is produced in autumn?

Most anthocyanins

When does chlorophyll production slow/stop?

As the night lengths start increasing.

Explain the process that happens to leaves when the night lengths begin increasing?

Shortening days/longer nights= oncoming winter

Steps:

1. Veins carry fluids into/our of the plants as layers of cells form at the base of each leaf

2. Clogged veins trap sugars in the leaf and promote anthocyanin production

3. The separation layer completion allows the tissue to seal off the leaf from the stem and prepare to fall off.

What factors influence the color and brilliance of leaves during fall?

The weather before and during the time of chlorophyll’s breakdown, temperature, and moisture.

Phototropism:

A plant’s growth towards or away from light.

Positive Phototropism:

Growth towards light (most plants).

Negative Phototropism:

Growth away from light (roots).

How does a plant go about phototropism?

1. The phototropins/photorecepters detect the different levels of light hitting the plant.

2. Different levels of phototropins impact auxin (hormone) production. The shady side gets flooded with auxins.

3. The plant is able to elongate on the side with all of the auxin, and bends towards the sun.

Photoperiodism:

Some plants require certain day conditions to flower. Plants measure length of the darkness.

Short Day Plants:

Need 6 hours of daylight, and an uninterrupted night to flower. (drops below a specific day length)

Ex: Rice

Long Day Plants:

Need 12 hours of daylight, and an uninterrupted night to flower. (rises above a specific day length)

Ex: Spinach and beets

Day Neutral:

Day length has no impact on flowering.

Water:

Makes up 95% of plants, carries nutrients through plant, and is necessary for photosynthesis.

Turgor Pressure:

Water pressure within a cell. More water= enlarged cells. (have to water plants completely)

Allow: structural support, flexibility/strength (plant won’t break in wind), and encourages root growth.

Loss of turgor pressure causes the plant to wilt.

Overwatering:

How most plants get killed.

Yellow/mushy leaves, wilting, root rot—> brown/black roots, and smelly soil.

Underwatering:

Drooping leaves, slow growth, brown leaf margins, wilting, yellowing leaves, and dry soil.

How to save an overwatered plant:

Hard to save.

1. Clear off saturate soil

2. Assess root condition; remove rotted ones

3. Repot in fresh soil and add drainage materials

How to save an underwatered plant:

1. Fully water soil

2. If soil is super dry: put pot in container of water (bottom watering)

Growing Media:

Anything that plants grow in which produces support and nutrients to the plant. May be 1 or many things; organic or inorganic.

Plants need:

nutrients, water, air, and support.

Examples of growing media:

Potting soil, sand, vermiculite, coconut coir, and tree bark.

Essential Elements:

Plant needs them to complete its life cycle, cannot be replaced by another element, need them for a specific biological function, and they must be required by a substantial number number of different plant species.

What are the essential mineral elements? (16)

Mg, K, Ca, Mn, Fe, Ni, Cu, Zn, Mo, B, N, P, O, S, Cl, H.

Which essential elements are nonmineral nutrients? (think: air and water)

Carbon, Hydrogen, and Oxygen.

What are the two types of mineral nutrients:

Macronutrients and micronutrients.

Macronutrients: (give examples)

Plants need lots of these: Nitrogen, Potassium, and Phosphorus. Deficiencies of these are quickly shown.

Signs of Nitrogen deficiency:

Yellow tissue in between veins (interveinal chlorosis).

Signs of Phosphorus deficiency:

Purple margins/edges (v shape)

Signs of Potassium deficiency:

Veins turns yellow, and leaf margins/edges wrinkle and turn brown.

Micronutrients:

Needed in smaller amounts, but are equally as important. Ex: Ca, Mg, Fe, Zn, etc.

Nitrogen Fixation:

Nitrogen in the atmosphere is a form of N that plants cannot use (N2). The forms plants can use (NH4 and NO3) are created by microbes breaking down organic matter in soil.

Are there any cases where plants can do nitrogen fixation on their own?

Yes, some plants can. Legumes, for example, have mycorrhiza (nitrogen fixing microbes) on their roots which can convert N into a useable form. These types of plants don’t need fertilizers with nitrogen.

Plant Hormones:

An internal plant growth substance that regulates physiological processes.

What do plant hormones control?

Cell elongation, cell differentiation, and physiological/natural plant processes.

Synthetic Hormones:

Fake hormones.

Natural Hormones:

Hormones made by the plant.

Inhibitors:

Prevent the action of hormones.

Hormones need to be:

Created internally (endogenous), organic compounds, regulating processes in low concentrations, be transported from their origin spot to a new location, and cannot be a nutrient or vitamin.

What are the 5 major growth hormones?

Auxin, Gibberellins, Cytokinin, Abscisic Acid, and Ethylene.

Auxin:

Stimulates a cut root to make new roots, thins fruit crops, conducts cell division and elongation based on sun exposure.

What is thinning a fruit crop, and why do trees do it?

Dropping a fruit before full development, so the tree can keep the extra energy for itself.

Gibberellin:

Stimulates enzyme production during germination and increases fruit size through cell elongation.

Cytokinin:

Stimulates cell division, promote shoot making/branching, and promotes development in tissue cultures.

Abscisic Acid:

Inhibitory; slows growth hormones, “stress” hormone (closes the stomata), and promotes apical dominance (where plant growth is happening).

Ethylene:

Last hormone to take action. Aging hormones, initiates a fruit to ripen and drop, and promotes senescence (deterioration with age).

Greenhouse:

A structure that allows us to regulate the climate conditions of a space, such as temperature and humidity.

How can we use greenhouses:

Grow plants that can’t handle cold climates year-round, growing plants in different climates, controlling climate conditions, preventing climate conditions, and experimentation.

What are the two types of greenhouses?

Lean-to (connected to other structures) Freestanding (separate from other structures)

What are the different forms of greenhouses?

Lean-to, hoop house (quonset), gothic arch, A-frame, barn style and even space.

Lean-to:

Connects to other structure, maintain heat well, durable, wind resistant, and good for small spaces.

Hoop House (Quonset):

Dome shaped, inexpensive, easy to heat; distributes air, allows more sunlight (no sharp walls). Usually in fields with ground as floor and plastic covers on the outside.

Gothic Arch:

Similar to hoop house, curved roof with a point, allows rain and snow to slide off sides- preventing damage.

A-Frame:

Original- high slanted sides; harder to heat

Modified- build with gable roofs (not as steep, short sides)

Barn Style:

Straight walls; good use of space.

Even Span:

At least on end attached to another building and both sides are even. MOST COSTLY.

(GH) What are the internal structure building materials?

Aluminum, Wood, PVC, and Steel.

(GH) What are the external coverings?

Polyethylene, Polycarbonate, Polyvinyl, Acrylic, Fiberglass, and Glass.

Aluminum:

Long lasting, durable, lightweight, and easy construction. NOT good at insulation and expensive.

Wood:

Easy to cut/secure. Wood rots, warps, and molds when wet.

PVC:

Lightweight, easy to move/change, good for small structures. Not much support, easily damaged, and less sturdy.

Steel:

Sturdy and more cost effective than aluminum. More difficult to cut, heavy, and rusts.

Polythylene:

Cost efficient, allows lots of light/heat, double layered/insulated (more heat). Can’t use PVC with this, yellows with exposure, and is easily damaged.

Polycarbonate:

Almost as transparent as glass, flexible or rigid sheets, can be used on any greenhouse type, 10-15 year lifespan, and highly impact resistant.

Polyvinyl:

Very durable, transparent, and good for windy, snowy, and hail conditions.

Acrylic:

High light transmittance, strong/impact resistant, new to greenhouse market= expensive, but has a warranty from manufacturers.

Fiberglass:

Durable, ridged, available in many different light transmittance levels. Deteriorates by UV light and a short 5 year lifespan.

Glass:

Maximum light transmission, lots of heat. Expensive/fragile, needs replaced, heavy, if too much heat/want more privacy= try frosted glass.

(GH) What are the flooring types?

Concrete, vinyl tiles, and crushed stone/gravel.

Concrete:

Easy to clean, drains water well, improves insulation, prevents weeds. Slippery when wet and not textured.

Vinyl Tiles:

Easy to install, waterproof, sanitary, and prevent s weeds. Slippery when wet.

Crushed stone/gravel:

Easy to install, inexpensive, and good drainage. Weed growth.

Irrigation:

Controlled watering of plants. Can be done manually or through systems.

Self Watering Trays/Capillary Mats:

Best for bottom watering, constant water supply, has a water compartment, plants absorb water as needed. Promotes deeper root growth, creates a humid atmosphere, low maintenance, and reduces disease from overhead watering.

Overhead Sprinklers:

Nozzles that can be adjusted. Saves time, waters from pre-existing water source, heads can get clogged with soil/lime, best for watering small shots prior to transplanting, and there’s a lot of water waste.

What s the difference in in ground and above ground sprinklers?

Inground is used for outdoor watering, and above ground is used for greenhouses.

Misting Systems:

Similar to sprinklers; best for seedlings, small water droplets, run longer than sprinklers, decrease temperature, and increase humidity (great for tropical plants).

Drip Irrigation:

Hose above/below ground that release one drop at a time, prevents soil from drying out, minimizes water waste, and easily clogs.