Greenhouse farming is a great way to economize on the use of space in your backyard, or if you’re into medium-scale farming, it’s a viable way to grow crops off-season.
Greenhouses help regulate the atmosphere surrounding the cultivated crops and keep out harmful pests allowing the plants to develop to their full potential.
Globally, greenhouses have become the default method of growing many kitchen garden vegetables. Greenhouse structures account for 473,466 hectares planted worldwide.
Factors Regulating Crop Growth Inside A Greenhouse
Greenhouse structures control four main factors that are crucial for plant growth. These are light, temperature, water, and air circulation. The question of what to grow in a greenhouse is largely dependent on these factors.
Light is a crucial component of photosynthesis, which is the process by which plants make their own food. Greenhouses regulate the light intensity, which in turn affects how much starch they build up and therefore how fast they are able to develop. Starch is important during a plant’s reproductive phase as it helps in the flowering process.
During periods of high light intensity carbohydrate metabolism takes place very fast so that the plant is able to elongate and reach maturity faster, this is why crops grow faster in sunny weather than in winter.
What makes greenhouses so effective in speeding up the growth rate of plants is that they trap UV light and warm up the interior of the structure. This is what is known as the greenhouse effect. Once these temperatures are raised, respiration takes place at a faster rate which in turn speeds up the plant's metabolism.
Inevitably higher temperatures go hand in hand with faster transpiration – the loss of water to the atmosphere – which if unchecked can lead to wilting of the plant. Transpiration, therefore, needs to be compensated for by having an irrigation system in place to replenish the plant’s water and nutrients.
It is also worth noting that at higher soil temperatures the roots are more active and able to take up nutrients and water at a faster rate, thereby boosting the overall rate of growth.
#3 Water and nutrients
Water is an important component of carbohydrates and also plays a role in the translocation, or movement of carbohydrates or starch from the leaves to the roots as well as other growing parts of the plant.
Nutrients, on the other hand, are involved in synthesizing proteins and other building blocks of the plant which are important for its development. Nutrients are taken up from the soil through the root system.
The soil type or media you use for growing your crop matters a lot in determining the availability of crucial nutrients for use by the plant. This presence is what we generally term soil fertility.
#4 Air Circulation
The other important ingredient during photosynthesis is carbon dioxide. Plants combine carbon dioxide and water in the presence of light to make starch.
The greenhouse effect mentioned earlier is important in building up carbon dioxide within the greenhouse which in turn increases the metabolism of starch.
Also, when there’s a high transpiration rate, humidity builds up within the greenhouse. The buildup of humidity and low air circulation encourage the development of pests and diseases within the greenhouse and must therefore be discouraged.
This may be done by incorporating shade nets within the greenhouse design to encourage ventilation to take place.
These factors are important for all plant types irrespective of which family they belong to.
Vegetable Types Grown In Greenhouses
Now, coming to what to grow in a greenhouse, there are plenty of options. Different vegetable types are grown because of their economic value as well as their nutritional value.
What you chose to grow will most likely be determined by the marketability of your product, although factors such as favorable climate also play an important role here.
Market Gardening vs. Export Production
Vegetables can be grown to sell locally at the grocery store or for export. In the former, the vegetables are sold at the farm gate or may be transported to the nearest town for sale in the market. In the case of export, these are normally processed and packed before export for use by big supermarket chains.
Tomatoes and Peppers
Vegetables belonging to the Solanaceae family are very popular for market gardening. These are mainly tomatoes and pepper.
Tomatoes and peppers do well in sunny weather conditions provided there is an adequate supply of water, especially during the fruit formation stage. Tomatoes can yield up to 60T per hectare if well taken care of, and take about two and a half months to reach maturity within the greenhouse environment.
They can also be grown using a hydroponics system (using mineral nutrient solutions dissolved in water, without soil) which is quite effective in controlling soil-borne pests and diseases.
When growing tomatoes or pepper it is important to carry out crop rotation to reduce incidences of crop damage by disease. Soil fumigation or sterilization can be done to kill off soil pathogens.
Tomatoes are sold fresh in the market or processed into other products such as tomato paste or juice. Peppers grown in the greenhouse are usually sold fresh in the market as well.
The world’s leading producer of tomatoes is China with an output of 3.5M metric tons annually.
Spinach, kale, lettuce, or broccoli are also popular vegetables grown in the greenhouse mainly because they take a relatively short period to mature and are easier to manage in terms of pests and diseases compared to other crops.
They tend to do well under cooler climates compared to tomatoes, and generally require more water during growth to make their leaves succulent.
These are great for marketing as salads and may be sold whole or packed for sale in the grocery store.
These are also known as vegetable confetti and are not to be confused with vegetable sprouts – as they are more varied in terms of colors, textures, and leaf shapes. They are a niche product in fine dining where they are used both as visual and flavor components.
Microgreens are suitable for garnishing in salads, soups, or on plates and are quite easy to grow. They are sown in plastic containers like nursery flats or punnets to facilitate growing and take 2–4 weeks between germination time and harvest.
Microgreens may be grown directly into the soil –popular with small growers – or using hydroponics.
Popular examples of microgreens include Beet, Peas, Tatsoi, Choi, and radish.
Grape vines require support when growing in the greenhouse or conservatory. Trellises are used for this purpose. They can be cultivated free-standing in the soil or in pots and are often pruned to manage their growth.
They require warm temperatures and good ventilation to encourage pollination and reduce fungal infections. Sometimes hand pollination is required to increase yields.
Greenhouse grapes are marketed fresh or may be processed into resins for use in the confectionary and baking industry. They may be packaged into plastic containers or without.
In conclusion, a greenhouse is a wonderful way to extend your growing season, protect your plants from pests and harsh weather conditions, and experiment with different vegetables that might not do well in your outdoor garden.
When deciding what to grow in your greenhouse, consider the size of your greenhouse, your location, and your personal preferences. Keep in mind that certain vegetables, such as tomatoes, cucumbers, peppers, lettuce, and eggplants, tend to thrive in greenhouse environments.
With a little bit of planning and effort, you can enjoy a bountiful harvest of fresh, delicious vegetables all year round.