Growing eggplants outdoors –if done rationally and on a scalable basis- can be a good source of income. In a few words, eggplant is a perennial plant, but growers in most cases treat it as an annual. Most commercial eggplant growers start the crop from seeds (hybrids) in an indoor protected environment. As they wait for the young seedlings to grow and be ready for transplanting (normally 4-6 weeks), they prepare the field. They till the land, they make the raised beds or furrows and they place a black plastic film through the rows. The black plastic film not only helps the soil become warmer, but also controls weeds. They also design and place the drip irrigation system. When they are ready for transplanting, they make small holes in the plastic film, where they dig small holes and plant the seedlings. Fertilization, Drip Irrigation and Weed Management is applied in most cases. When plants reach a height of 40 cm (16 inches), most growers stake the plants, so as to support plant growth, improve aeration and facilitate harvesting some weeks later. Thinning is also applied. Commercial eggplant growers remove some sprouts in order to encourage the plant to devote its resources in fewer but bigger and tastier fruits. Most commercial eggplant varieties can be harvested 60-100 days after transplanting. Time from Planting to Harvesting depends on the variety, climate conditions and the age of the seedlings planted. Harvesting can only be made through hand scissors or knives and is normally performed in more than one session. After harvesting, eggplant growers plow and destroy the remaining of the crop. They may also rotate the crop (with cabbage, corn, legumes and others), in order to control diseases and prevent soil from depleting.
The restrictive factor when growing eggplants is always the climate. The plant comes from warm climates. It is a plant sensitive to low temperatures and frost. It requires on average temperatures from 21 to 30°C (70 to 85 °F), while soil temperature should not fall below 20°C (68°F). Cool weather during growth period will inhibit plant growth and it is nearly impossible for shocked plants to recover and give an acceptable yield.
First of all, it is crucial to decide the growing method as well as the varieties of eggplant that thrive in our area. There are 2 methods to grow eggplants: From seed and from seedlings.
Growing Eggplant from Seed
Eggplants are long-period crops. They need 60 to 100 days from transplanting to maturity point. However if you are planning to grow eggplant from seed, there are some facts you need to know. First, eggplant seeds require at least 21 °C (70 °F) soil temperature in order to germinate. Second, it is very important for the seed to have optimum moisture levels in order to sprout. Over irrigation can be harmful. Eggplant seeds germinate approximately in 8-17 days depending on the weather and soil conditions. Producers in areas with frost danger, prefer to sow the seeds in seed beds under controlled conditions and then transplanting them into their final positions. They often use turf as substrate for optimum aeration. In areas with hot weather during spring, producers may sow the seeds directly in the field. Although this is a cost effective method, it generally results in greater problems later, as the crop matures.
Growing Eggplant from Seedlings
If you prefer to start eggplant farming from seedlings, it is crucial to buy disease-free plants from a legitimate seller. The optimum time for transplanting is when they have 3-4 real leaves (4-6 weeks). Transplanting will most probably fail, unless the soil temperature is above 20 °C. Thus the best period for eggplant transplanting, in most countries is during the second half of spring.
Soil Requirements and Preparation for Eggplant Cultivation
Soil can rarely be a restrictive factor, when we grow eggplants. However, the plant thrives best in middle to sandy soils with proper aeration and drainage. It normally has greater drought tolerance than tomato plant has, due to its deep roots. On the other hand, eggplant does not like soggy soils. The optimum pH levels range from 6 to 7. There are cases in which growers managed to grow eggplants and achieved average yields in soil with pH 8,5, but with special handling.
The basic soil preparation starts 1 month before transplanting eggplant seedlings. Farmers plow well at that time. Plowing improves soil aeration and drainage. At the same time plowing removes rocks and other undesirable materials from the soil.
One week later, many farmers apply a pre-planting fertilizer such as well rotted manure or synthetic commercial fertilizer, always after consulting a local licensed agronomist. Most farmers integrate top dressing at the same day, using tillage tractors. The next day is probably the right time to install the drip irrigation pipes. Following the installation, some farmers can apply soil disinfection substances through the irrigation system, in case soil analysis has revealed soil infection problems (ask a licensed agronomist in your area).
The next and most important step (especially in countries with non optimum soil temperature during the planting period) is the linear polyethylene coating. Many producers cover the rows with black or green Infrared – Transmitting (IRT) or black plastic film. They use this technique, in order to maintain the root zone temperature at optimum levels ( >21°C or 70°F) and prevent weeds from growing.
Eggplant Planting Outdoors and Plant spacing
In many eggplant producing countries, the most suitable time to plant eggplants outdoors, is during the second half of spring. At that time, temperatures are close to 21 °C (70 °F) and the danger of frost has passed in most cases. However, in the United States (Florida) and in United Arab Emirates, planting normally takes place during August and harvesting starts from November onwards. Farmers generally prefer seedlings aged from 4 to 6 weeks. At this point they have developed 3-4 real leaves. There are cases in which growers plant 8-10 weeks old seedlings. This technique will normally result in fewer days from transplanting to harvesting.
After all the preparation steps started 1 month before planting (plowing, basic fertilization, installation of the irrigation system and plastic film covering), we can proceed with transplanting. Growers label the exact points on the polyethylene mulch where they will plant the young plants. They then dig holes on the plastic and plant the seedlings. It is important to plant the seedlings at the same depth as they were at the nursery.
Producers plant eggplants at single or twin rows. A common pattern for single rows planting is: 0.4m to 0.8m (18-35 inches) distance between plants on the row and 1.2m to 1.5 m (4-5ft) distance between rows. For twin rows planting, many growers prefer: 0.4m to 0.8m (18-35 inches) distance between plants on the row and 0.9m to 1.2m (3-4 ft) distance between rows. Following this pattern, we will approximately plant 10000-20000 plants per hectare. However, this is not always the case. Many farmers plant from 25.000 to 35.000 plants per hectare. The distances and the number of plants, depend on the eggplant variety, environmental conditions and of course the yield goals of the producer. (1 hectare = 2,47 acres = 10.000 square meters).
Most eggplant producers use stacking for their eggplants. There are several advantages of using this technique. First of all, stacking prevents foliage and fruits from touching the ground, while at the same time leaves extra space for aeration. Furthermore, harvesting becomes much easier. The right time to start stacking, is when eggplants have reached a height of 40 cm (16 inches). Farmers tie every plant with wooden stakes 0.5cm (1 inch) thick and 1-1.5m (50-60 inches) long.
Eggplant’s Pruning – A controversial method
Many eggplant producers prefer to prune their eggplants, while others claim that pruning delays the development and fruit setting of the plant. Those who prune their plants remove most of the peripheral stems of the plant early during the first stages of development, when it has 3-4 stems. With this method, they force the plant to develop further through the two v-shaped main stems. They keep removing excess foliage that prevents proper aeration, during the entire growing period. Thus, they protect the plant from humidity favored infections. Moreover, some producers remove most of the double flowers, leaving the most vigour ones on the plant. This method helps the plant distribute more nutrients to the remaining flowers. These flowers will eventually give bigger fruits.
Eggplant Water Requirements and Irrigation Systems
According to State University of Utah, the proper irrigation plan for eggplants, is to apply 2.5-5cm water (1-2 inches per week).
Of course, water requirements can be totally different under different weather and soil conditions. For example, heavy clay soils normally need less irrigation than a sandy soil. Moreover, on rainy days or on days with high humidity, we may not require irrigation at all. On the other hand, a dry day with high temperatures may require more than one irrigation sessions. Different eggplant varieties also have different water requirements.
As a general rule, water requirements of plants increase from pollination to fruit setting. Many producers in Mediterranean countries prefer to irrigate their eggplants providing 1 liter οf water per plant every 2-3 days, during their first stages. During the fruit setting stages and as the temperature increases a lot (35 oC or 95oF), they increase irrigation sessions, due to the high needs of the plant. At this stage, they irrigate daily, or even twice a day depending on the weather conditions. They irrigate their eggplants early in the morning if the day is cloudy, adding one more irrigation sessions at night, during hot periods. Watering the foliage has been linked with diseases outbreaks. In general, excess humidity, especially on foliage, may favor diseases outbreaks. On the other hand, water-stressed plants are more susceptible to diseases.
The most commonly used irrigation system is drip irrigation. Most producers use multiple or one – use drip strips with 20cm (7.8 inches) distance between drips.
Eggplant is self-pollinated. However, it has been reported that bees may improve pollination, and thus fruit setting and total yield per hectare.
Eggplant Fertilizer Requirements
First of all, you have to take into consideration the soil condition of your field through semiannual or annual soil testing, before applying any fertilization method. No two fields are the same, nor can anyone advise you on fertilization methods, without taking into account your soil’s test data, tissue analysis and crop history of your field. However, we will list the most common eggplant fertilization schemes, used by a considerable number of farmers.
The most commonly used fertilization method is “fertigation”. Producers inject water soluble fertilizers inside the drip irrigation system. In this way, they can provide the nutrients gradually and give the plant the proper time to absorb them.
Nowadays farmers make from 0 to 10 fertilizers applications throughout the 2 to 3 months period from transplanting to harvesting. Many farmers apply well rotted manure towards the rows, about two months before planting. They also apply a pre-planting fertilization high in Phosphorus about a week before planting and start the fertigation 10 days after planting. At this point, they apply a Nitrogen- Phosphorus- Potassium 13-40-13 fertilizer, enriched with trace elements (micronutrients). High Phosphorus levels at the first stages will help plants develop strong root system. Additionally, micronutrients makes it easier for plants to overcome any stress conditions caused by the transplanting. 3 days later, they repeat the 13-40-13 application.
During the following days, they apply once a week water soluble N-P-K 20-20-20. They continue the 20-20-20 applications until the fruit reaches ⅔ of its final weight. From this point, they start to increase Potassium levels by providing eggplants with KNO3 and/or Κ₂SO4 . At these stages, plants have greater needs for Potassium in order to create big, well shaped fruits.
Another common fertigation program for eggplant involves Urea, Potassium Nitrate and EDDHA. Urea is injected into the irrigation system 2-4 weeks from transplanting, KNO3 is injected 6 weeks after transplanting until the last stages before harvest, while EDDHA is administered throughout the growing period.
However, these are just common patterns that should not be followed without making your own research. Every field is different and has different needs. Checking the soil condition and pH is vital before applying any fertilization method. You can consult your local licensed agronomist.
Eggplant Pests and Diseases
The first precaution against pests and diseases is crop rotation and tillage. The second is to purchase only certified disease free seeds and seedlings.
Colorado Potato Beetle
Colorado potato beetle (Leptinotarsa decemlineata) -despite its name- attacks not only potatoes but also eggplants. The beetle overwinters on the ground and during the spring starts to reproduce. Larves of the beetle chew the eggplant leaves, causing serious damage to the entire crop. Companion planting of eggplant with beans has been reported to protect eggplants from beetle attack.
A good technique is to constantly monitor their population. If the number is over the tolerable limits, then you may consider to intervene. There are biological as well as chemical solutions on the market, which of course should always be used under Good Agricultural Practices standards and supervision from a local licensed agronomist .
Liriomyza bryoniae, is one of the most important enemies of the eggplant. It resembles a tiny fly, however, the larvae of this insect attack eggplant leaves, causing characteristically white stoas and holes. Eventually, the plant drops the leaves due to their inability for photosynthesis. Moreover, the holes that the larvae creates, favor the infection of harmful microorganisms.
A good technique is to constantly monitor their population. If the number is over the tolerable limits, then you may consider to intervene. There are biological as well as chemical solutions on the market, which of course should always be used under GAP standards and supervision from a local licensed agronomist .
Verticillium dahliae is a serious fungal pathogen that attacks the eggplant, causing plant death. The first signs start as we observe slow wilt on the foliage, which gradually turns brown. Infected plants may have slower development than the healthy ones do. Disease control begins with proper precautionary measures. These include: weed control and safe distances between plants along with proper pruning for optimal aeration. The general condition of the plants (nutrients and water level, sun exposure) can also boost their immunity. Chemical treatment is used only if the problem is severe and always under supervision from a local licensed agronomist.
Phytophthora (Phytophthora infestans) is a serious fungal pathogen that attacks the eggplant.
Symptoms most commonly appear on leaves, during days with high humidity levels, especially when cold nights are followed by hot days. When our plants are infected by phytophthora, we will probably observe offwhite, yellow or gray spots which periodically turn brown.
Eggplant Harvest, Yield and Storage
The majority of eggplants reach their full maturity and are ready for harvesting 60-80 days after transplanting. As a rule of thumb, farmers harvest eggplants before their seed turn brown.
Eggplants are harvested by hand and in more than 1 harvesting sessions. In large commercial farms of the US, farmers perform 1 harvesting session per week for 3-4 weeks in the same field. Commercial growers after years of practice collect 12-15 full size eggplants for every healthy plant, but this also depends on variety and desired size of the harvested fruit.
Eggplant Yield per Hectare
A good yield after years of practice is 25 to 40 tons per hectare. There are cases in which farmers harvested 60 tons per hectare, or even more. Of course, such high yields can only be achieved under certain conditions (intensive farming and many years of experience).
Eggplants are then transferred to cool but not freezing (10°C – 50°F) storage areas, so that a potential weight loss is avoided.
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