Building Your Own Greenhouse by Max Clarke - HTML preview

/ Home / Recreation & Hobby / Building Your Own Greenhouse

PLEASE NOTE: This is an HTML preview only and some elements such as links or page numbers may be incorrect.
Download the book in PDF, ePub, Kindle for a complete version.

"Building Your Own Greenhouse" by Max Clarke

Page 64 of 123

accordance to the weather conditions in your area. Strict

adherence to these codes helps to prevent freezing or cracking

of the foundation of your greenhouse.

Mark chalk lines across the ground area for your greenhouse

and dig trenches according to your local building codes along

the marked chalk lines. Set level concrete footings eight

inches wide into the trench. Your steel rod footings should be

tied horizontally or vertically inside foundation forms before

the pouring of concrete.

Flooring of Your Greenhouse

Ensure the ground area across your flooring to be as level as

possible. Dump in gravel and smooth it.

Next, pour in crushed stone and tar paper. You could use

builder's heavy plastic too. Then, set the mesh and pour in the

concrete.

In hot weather, cover concrete with plastic and sprinkle water

intermittently to help the flooring become strong and sturdy.

"Building Your Own Greenhouse" by Max Clarke

Page 65 of 123

Leave two-inch drainage holes four feet apart in the

foundation. After the footings settle well into the foundation,

remove your forms and fill the foundation with gravel or dirt.

Installing gravel or tile drainage channels with drainage holes

can allow easy drainage within your greenhouse.

"Building Your Own Greenhouse" by Max Clarke

Page 66 of 123

Selecting the Right Lights

Greenhouse cultivation does not depend on natural weather

conditions. It all depends on the artificial environment you

create within your greenhouse. Therefore, your artificial

arrangements should be in accordance with the natural

requirements of plants for healthy growth.

Light Requirements

Sunlight forms the essence for the growth of any plant. All

greenhouses allow easy penetration of sunlight. However,

available sunlight may not be sufficient during the winter

months and on cloudy days. Therefore, you need to arrange

artificial lights.

"Building Your Own Greenhouse" by Max Clarke

Page 67 of 123

Selection of artificial lights depends on:

Your plants’ requirements

The area of your greenhouse

Availability and intensity of sunlight

Many different types of lights are available; fluorescent lamps,

incandescent lamps, mercury vapor lamps, neon lamps,

sodium vapor lamps and others.

Different color combinations of lights exist. Color choices

depend on the requirements of your plants.

Lights could increase the temperature within your greenhouse

if they are in addition to reasonable sunlight. Choosing lights

that emit more light and less heat energy can help to maintain

greenhouse temperatures at appropriate levels.

Types of Lights

Fluorescent lamps: These lamps are most popular for use in

greenhouses. These lamps are available in various colors. The

highest preference is for white fluorescent lamps. These lamps

"Building Your Own Greenhouse" by Max Clarke

Page 68 of 123

provide more light with less heat. High intensity fluorescent

tubes of 1500 ma can deliver a high wattage of around 2000-

foot candles.

Soft lights of this type contain the entire spectrum of sunlight.

Having such lights over seedlings with poor growth can boost

their growth. Restricting use of these lights over smaller areas

can be a good option.

Incandescent lamps: Incandescent lamps are available in

different wattages, ranging from sixty to five hundred watts.

These lights can make the plants think days are longer in your

greenhouse. You can vary foot-candle levels by adjusting the

spacing and mounting height of the lamps over your plants.

High-intensity discharge (HID) lamps: As the name

suggests, these lamps provide high emission of light. These

lights last for a long time; for over five thousand hours.

Efficiency of these lights increases with the addition of sodium

and metal-halides.

Metal Halide Grow Lights: These lights emit the blue and

violet colors of the spectrum. Such light is normally available

during spring. These lights best suit growing plants and

support their early developmental stages to promote stronger

roots, increased resistance to diseases and a more compact

green growth.

High-Pressure Sodium Lights: These lights produce orange and red colors of spectrum that encourages plant growth like

"Building Your Own Greenhouse" by Max Clarke

Page 69 of 123

you see in autumn and early fall. Therefore, this light suits

plants in a mature stage.

You can use a convertible grow light system to alternate

between metal halide lights and high-pressure sodium lights.

You can use metal halide lights for starting seedlings and then

shift to high-pressure sodium lights as they grow into mature

plants.

This can save you money compared to purchasing separate

lighting systems.

"Building Your Own Greenhouse" by Max Clarke

Page 70 of 123

Part-IV: Environmental Systems

Cooling, Ventilation and Your Greenhouse

Greenhouses essentially lock in sunlight to provide a more

suitable environment for plants to grow. But, trapped sunlight

should not exceed required levels. Otherwise, your plants may

wither. Use adequate cooling strategies within your

greenhouse to maintain optimum temperature and humidity

levels.

Cooling and Ventilation of Greenhouses by Plants

Plants have an inbuilt mechanism to cool themselves. They

regulate their temperatures by evaporating water through the

"Building Your Own Greenhouse" by Max Clarke

Page 71 of 123

process of transpiration. Plants can keep themselves cool in

greenhouses if there are many leaf surfaces.

If your greenhouse houses plants with many large leaves, the

atmosphere in the greenhouse can be cooled to a considerable

extent.

To help plants transpire easily and effectively, you should

supply them with lots of water. Irrigate your plants in the

greenhouses extensively and frequently. This neutralizes salt

levels in plant roots so that high salt levels do not interfere

with their intake of water.

Next, provide sufficient ventilation within the greenhouse so

that moist air transpired through leaf surfaces goes out and

cool dry air enters greenhouse. Employing proper air

"Building Your Own Greenhouse" by Max Clarke

Page 72 of 123

circulation techniques can help provide this environment for

your plants.

Cooling and Ventilation by Blocking Sunlight

You can maintain cool temperatures in the greenhouse by

blocking sunlight. Fix retractable or fixed sunshades to restrict

the amount of sunlight entering your greenhouse. Maintain an

adequate supply of sunlight for plants to photosynthesize their

food.

Light requirements of plants depend on the specific species

and the intensity of available light too. If your greenhouse has

many crops with dense foliage, use little restrictive shades so

that these plants and their foliage do not suffer from lack of

adequate sunlight.

Use semi-permanent shade materials like screens and

coatings. These are very flexible in adjusting light

requirements.

Ventilation Equipment

Roof vents help remove hot air from within the greenhouse

and replaces it with cool outside air. Hand-operated roof vents

require regular temperature checks. You have to open and

close vents according to the changes in outside weather. This

is necessary to prevent excessive cooling or heating of air

within the greenhouse.

"Building Your Own Greenhouse" by Max Clarke

Page 73 of 123

Install sidewall or gable exhaust fans underneath curtains to

remove trapped, heated air.

Curtains pulled in an east-west direction prove useful in

regulation of penetrating sunlight. Use curtains of open-weave

materials so that hot air rises through the roof.

Ventilation systems function in relation to the area of your

greenhouse. The height of your greenhouse does not play any

role in effective ventilation. An effective ventilation system

should be able to exhaust eight to ten cubic feet of air per

minute from every square foot of your greenhouse.

Further, ventilation should be uniform all over your

greenhouse. If outside temperatures are very high and dry,

use ventilation systems in combination with the natural

transpiration systems of your plants to maintain necessary

coolness within the greenhouse.

This requires frequent regulation of the air in the greenhouse.

Another way of cooling your greenhouses is through use of

mechanical cooling; refrigeration or air-conditioning. This

technique could prove very costly.

Other cooling techniques include mists, fogs, pads and fan

systems and sprinklers. All these work fine if moisture content

in the air is not perfect.

Mists, fogs, and sprinkler systems can function independently

or synchronize with other mechanical ventilation systems. But,

"Building Your Own Greenhouse" by Max Clarke

Page 74 of 123

you should regulate air and humidity temperatures for these

systems to function smoothly. You can switch them on and off

intermittently.

These systems have their own problems too. Impurities in the

water could lead to clogging and foliage could suffer from

continuous wetting too. You can regulate the even dispersion

of water by regulating the size of particles and avoid chances

of over-wetting.

However, effective cooling depends more on the amount of

evaporation.

Shading equipment includes roll-up screens of aluminum,

wood, vinyl, paint-on materials or plastic shades. These

shadings function with the help of nylon ropes or pulleys. You

can adjust the shade according to outside weather conditions.

You can use shading compounds too. Apply them on the

exterior of the greenhouse glass.

"Building Your Own Greenhouse" by Max Clarke

Page 75 of 123

Plants in a greenhouse

Automated Cooling and Ventilation Techniques

Automated cooling and ventilation systems can offer

systematic and controlled regulation of temperatures within

greenhouses. These automated techniques do not require you

to maintain personal controls. Systems have an in-built

mechanism that manages irrigation levels, operate suitable

shading systems and provide necessary ventilation by

operating relevant cooling.

This occurs by coordinating various pieces of automated

equipment in relation to the varying requirements of your

greenhouse.

"Building Your Own Greenhouse" by Max Clarke

Page 76 of 123

Automated vents have a special thermostat and electric motor

systems that remain open to allow the necessary amount of

cool air. They also allow warm air to flow out similarly.

Maintenance of such moderate temperatures within a

greenhouse promotes healthy growth of plants.

Automated systems function independently and you do not

have to keep changing them according to different seasons.

You can use a single thermostat, or a controller with a

temperature sensor. Sensors should always be in the shade

and located at around plant height. White sensor boxes can

reflect solar heat and give accurate temperature readings.

"Building Your Own Greenhouse" by Max Clarke

Page 77 of 123

Understanding Heating Methods,

Systems, Sources, and Distribution

Heating systems are essential for greenhouses to function

normally. Solar energy is the main source of heat energy

necessary for greenhouses. Nevertheless, you should have

adequate alternative heating systems to maintain systematic

heating all year through.

These heating systems can regulate temperatures within

greenhouses and maintain a conducive environment for plants

to grow and flourish.

Heating Systems and Methods

There are different heating systems for regulating

temperatures within greenhouses. You can use that which best

suits your greenhouse requirements.

Pipe Heating: This has many metallic or plastic pipes

carrying steam or hot water spread across the greenhouse.

These pipes heat the greenhouse through convection and later

radiate heat directly to the leaves. Overhead pipes should be

"Building Your Own Greenhouse" by Max Clarke

Page 78 of 123

closer to plant surface for effective heating without loss

through radiation. Similarly, hot pipes passing near the ground

in the greenhouse can stimulate better circulation of hot air.

Pipes passing through the middle of greenhouse can provide

excellent radiation of heat. Take care to avoid scorching of

plants through heat from the pipes.

Warm Floor Heating: This heating system involves placing

hot water pipes below the concrete of the greenhouse. This

system helps in uniform heating of the entire ground surface

of the greenhouse and uniform distribution and circulation of

heat throughout the plant canopy.

Heating the root system promotes plant growth. But, this

system may be too expensive for many.

Bench Heating: This heating system involves placing hot

pipes on, or under, the benches. This can assure uniform

spreading of the heat across plant roots and improve air

movement extensively. Although this system can reduce the

incidence of root pathogens by warming soil, it can cause

"Building Your Own Greenhouse" by Max Clarke

Page 79 of 123

excessive stress on the plants closest to heaters. Similarly,

plants farthest from heaters may not receive equal benefit.

Air Heating: Overhead heated air directed through fans and

perforated polyethylene tubes can heat greenhouses quickly.

You have to maintain perfect on-and-off timings to regulate

temperature within your greenhouse. This system could prove

expensive.

Central Heating Systems: These heating systems generate

heat from a centralized location, normally a huge boiler. This

heating system proves efficient for huge commercial

greenhouses, although installation and maintenance costs are

expensive. Hot water produced in a boiler, pumps into your

greenhouse at 180° F. This system also requires extensive

plumbing and circulating systems to maintain the necessary

supply of heat. You can use steam centralized heating systems

as they provide heat at 215° F.

Radiant heaters: These heaters have aluminum tubes with

reflectors. Combustion of fuel within the tubes cause

temperatures to rise to around 900° F. Reflectors direct the

infrared radiation downwards to plant surfaces and benches.

These surfaces absorb radiation and heat. These heaters

require low-flow or poly-tube fans to maintain necessary air

circulation.

The number of heating units should be such that there are no

cold spots. Initial costs are high.

"Building Your Own Greenhouse" by Max Clarke

Page 80 of 123

Fuel Sources for Heating Systems

There are different fuel sources for heating systems of

greenhouses. You can choose fuel according to cost,

availability, pollution regulations, storage possibilities, boiler requirements and maintenance requirements.

Popular Fuels:

Natural Gas: This fuel source may be currently one of the

most inexpensive and has low maintenance costs. It offers

clear burning and there is no need for storage tanks.

Propane and Butane: Although similar to natural gas, they

are more expensive and require storage tanks.

Oil: You need storage tanks to keep this fuel source. It

requires regular boiler maintenance as it does not burn

cleanly.

Wood chips or Logs: These fuel sources require huge

storage area and extensive handling with regular boiler

maintenance and cleaning.

Coal: This low-cost fuel requires extensive storage space and generates immense pollution too. You require regular boiler

maintenance.

While using coal, oil, or gas heaters, there should be a

constant supply of fresh air to avoid any build-up of carbon

monoxide. Fans can help to maintain the necessary air

circulation within greenhouses.

"Building Your Own Greenhouse" by Max Clarke

Page 81 of 123

Heat Distribution inside Greenhouse

Even distribution of heat inside a greenhouse is as essential as

generation of heat. Uneven distribution can cause many

problems.

Some of the most important are:

• Irregular growth of plants

• Improper maturation

• Excessive dry regions, and

• Stunted growth of plants

Different heating systems generate and distribute heat in

different ways. Centralized heating systems can be through

hot water or steam. Heat distribution takes place through a

network of aluminum, cast iron, or copper pipes. Steam offers

less resistance and therefore you can use pipes with a smaller

diameter. Steam additionally delivers higher heat than hot

water. Efficient distribution of heat requires proper placement

of pipes. This can increase heating and reduce heat loss.

"Building Your Own Greenhouse" by Max Clarke

Page 82 of 123

Potted plants in a greenhouse

Placing pipes in layers can reduce heating efficiency. Instead,

place pipes singly.

Unit heaters are not very efficient in distributing heat.

Temperature differences occur along the length of a

greenhouse. Temperatures close to the heater are high. Use of

multiple unit heaters across each other can solve this problem.

It helps to maintain uniform heat across the entire length and

breadth of the greenhouse.

Additionally, you can use horizontal airflow fans to promote

movement of air within greenhouses.

"Building Your Own Greenhouse" by Max Clarke

Page 83 of 123

Unit heaters mounted onto greenhouse gables and connected

to polyethylene jet tubes can distribute heat evenly. In cooler

seasons, you can switch off the fuel source and firebox and

use a fan of unit heaters with polyethylene tubes with outside

louvers.

Heating systems placed low in the greenhouse can help to

maintain warmer temperatures. Leaf surface temperature

above dew point can prevent condensation. It helps prevent

various greenhouse diseases.

Other heating systems should be as close to the canopy as

possible. This saves lots of energy too.

"Building Your Own Greenhouse" by Max Clarke

Page 84 of 123

Calculating Energy Requirements

for Heating Systems

Energy requirements for heating greenhouses are not the

same everywhere. It depends on various factors, including:

Size of the greenhouse

Difference in outside temperature and temperature within

greenhouse, and

Single or double layered covering of glasshouse in plastic or

glass.

Normally, greenhouse sellers educate you about heating

requirements of your specific greenhouse so that you can

make use of these systems too. You can calculate heat energy

requi