Cariboo Gardening Guide 2003
* Greenhouse Growing *

Whether you are wanting to grow your own bedding plants or keep yourself in fresh produce for the year, there are many things to consider when starting off plants in a greenhouse.

If you do not have an existing greenhouse already, but would like to build your own, you will have to consider the following factors:

1. Greenhouse Plans
2. Location
3. Covering Material & framing
4. Venting
5. Heat Source

For most recreational greenhouse growers, a greenhouse with an area of roughly 170-200ft² will be adequate. A great source for greenhouse plans is the library or the internet. Sites such as www.h2othouse.com offers a variety of plans for greenhouses, coldframes, benches etc…. When selecting a plan, think about which type of covering material and framing methods will be feasible for you.

Once you decide on a plan, the next step is to select the location for your greenhouse. Ideally, your greenhouse location will be free of shade, close to the house for water, electricity etc…, and have firm ground to support the framing. The recommended exposure is to have your greenhouse ridge line running North to South as this is where it will receive the most light.

There are many different options when it comes to selecting a covering material for your greenhouse. The covering material selected will also dictate which type of framing you will need to use. The different types of covering material are:

1. UV Treated Poly – Most cost effective at about 18¢ per square foot. Should have 2 layers of 6mil poly for heat retention. Install an inflation fan to provide air layer in between. Snow slides off easily. Can use any type of framing (metal, pressure treated wood, etc) +/- 5 year life span
2. Lexan – Good light filtration. Built in air layer. More expensive than poly at $2.00 per ft.²
3. Glass – Expensive. Should be tempered to avoid breakage in hail storms. Best light filtration. 15 year + life span Difficult construction techniques.
4. Fibreglass – Reasonably economical. Durable. Bad heat retention. Good light diffusion. Can layer on top with poly to help seal in heat.
5. Coroplast – Breaks down in the sun in 2-3 years. Economical and easy to install for end walls. Good heat retention.

All greenhouses should have a means of ventilation as they can heat up very quickly once the sun comes out. This can be as easy as opening the door when it becomes too hot or you can install a simple fan at the end of your greenhouse and a gas shock opening vent at the other end so your greenhouse doesn’t pull itself down when the fan comes on.

Most smaller greenhouses can be adequately heated with an electric heater. A 1,000 watt electric heater should be fine for most greenhouses up to 200 ft2. Heaters placed under the bench to warm soil are ideal. The temperature should be monitored frequently in the greenhouse with an air thermometer. Move it around during the day to see where the cold and warm areas are. Day Temperature should be kept to around 75° and Night Temperature ideally should be around 60ºF, although as long as it doesn’t freeze, plants will not suffer too much. Temperature should not exceed 85ºF. Soil thermometers are also very useful during germination.

PLANNING
Once you have your greenhouse, you will have to decide what you want to grow. The winter is a great time to plan for next year. Peruse the seed catalogues and make a list of all the seed you would like to order. Catalogues like Stokes have all the information listed with each plant such as temperature required and days to germination. This information will help you plan when to seed each crop. Secondly, you will want to plan you greenhouse space according to your needs. Even if you are using your greenhouse strictly for tomatoes planted directly into planting beds, most greenhouses benefit from a small potting table with cupboards or shelves underneath to store gardening tools, pots, etc…. If you plan on starting your own seed, benches are recommended to keep the flats off the ground.

SEEDING
When seeding, clear plastic domes placed over the seed flat will help retain humidity and speed up germination. They should be removed once seedlings emerge & during hot days. To protect seedlings from Damping Off, which is the product of a fungi located in the soil that can cause seed to decay as well as rotting off seedlings & cuttings, apply the fungicide NO-DAMP to the seed flat as a preventative. Damping off is also due to poor air circulation and tall weak stems. If seedlings are ‘stretching’ or growing too quickly, you may have to lower the temperature to slow down their growth.

WATERING & FERTILIZATION
Water & Soil Testing should be done yearly, or whenever plants are not growing vigorously. Testing allows us to determine what should be added to improve soil & or water quality. There are many tests available that will allow you to test pH as well as levels of nitrogen (first number in a fertilizer analysis – responsible for green growth), phosphorous (Second number in a fertilizer analysis – responsible for blooms, fruit production, rooting) and potassium (last number in a fertilizer analysis – responsible for disease resistance & hardiness).

The general accepted pH for most plants is around 6.0 – 7.0. If your pH is extremely alkaline (high) or acidic (low), then it may prevent the plant from drawing up nutrients and you may start noticing signs of fertilizer deficiencies in the plant. If you need to raise your pH you can use Dolomite Lime. As our soil pH levels around Quesnel are usually high, you can lower your pH by using products such as aluminum sulphate, sulphur, or peatmoss.

Once plants are actively growing, make sure they have all the nutrients they need to remain strong & healthy by applying a water soluble fertilizer that contains micro nutrients such as iron & magnesium as well as nitrogen, phosphorous & potassium at least once every two weeks. For organic growers, there are a variety of products such as kelp, compost tea, bonemeal, bloodmeal, or the ever popular Fish Fertilizer that will help your plants stay in tip top shape. The healthier your plants are, the more able they are to resist disease.

GREENHOUSE SANITATION
Keeping a clean greenhouse is the best way to help prevent disease & insect infestation. By adhering to the following simple rules, you will help your plants remain as pest free as possible.

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