Position for growing strawberries
Lowlands connected to river valleys or their tributaries due to low altitude (up to 200 m), no slope or with a slight slope (3 to 5%), which suits strawberries best, proved to be the most favorable locations for growing strawberries.
Choice of position for raising strawberry plantations
Strawberries give the best results on soils with a neutral reaction and a lighter structure (made of gravel-sand, loam and clay deposits in appropriate proportions). With regard to climatic factors, only early autumn or late spring frosts can cause a problem, therefore it is recommended to avoid frost areas or areas with frequent occurrence of frosts. Shortage of irrigation water during the growing season should not be a problem if strawberries are planted near rivers and tributaries. If this is not the case, irrigation is mandatory. The area must also not be known for gusts of wind.
Preparing the soil for planting strawberries
Before preparing the soil itself, it is very important to take care of the crop rotation. The strawberry comes to the same surface only after 3 years. It is also recommended not to plant strawberries behind certain crops such as potatoes, tomatoes or chrysanthemums or some other types of strawberries.
Cereals (oats, barley, etc.) and legumes are good pre-cultures for strawberries.
This is followed by soil preparation, which usually begins with plowing. Strawberry requires plowing to a depth of 30 to 40 cm. Plowing must be done 15 to 30 days before planting. When plowing, it is recommended to plow previously grown crops for green fertilization. This is especially true for the northwestern part of Croatia, where heavier soils prevail. This is followed by plate-making in order to level the surface and pulverize the soil.
Since the strawberry’s root system extends for the most part to a depth of 20 cm, it is necessary to introduce the fertilizer so deep that it is immediately available to the plant. First, it is fed with 800 to 1,000 kg/ha of complex NPK fertilizer of the formulation 7-14-21, and then 30 to 50 t/ha of manure is introduced into the soil. The fertilizer is introduced deeper into the soil by repeated spreading and mixing well with it. When the preparation is finished, using a harrow or tiller, the surface of the soil is finely divided and leveled so that the beds can be made.
Selection of strawberry planting material
The basis of successful strawberry production is high-quality, varietal-pure and healthy, i.e. virus-free planting material. When choosing strawberry seedlings, it is necessary to take care that the central bud is noticeable and fresh.
Damaged, dry or rotten leaves should be removed. If the tips of the roots are dry, they should be refreshed by spraying with water, and if the roots are too long, they should be shortened by 1/3 of their length.
There are several categories of strawberry seedlings.
Today, green seedlings are less and less represented in production due to their lower quality compared to other categories.
Frigo seedlings are most often used today. This type of seedling has experienced a real expansion in recent years due to its higher fertility potential compared to green seedlings. They are taken at the end of the growing season, in November or December. After removing from the ground, frigo seedlings are cleaned of leaves and soil, packed in 25 pieces, soaked in one of the fungicides, placed in plastic bags and stored in refrigerators where they are kept at a temperature of -2 ºC. Then they are dormant and can be stored for the next 10 months. They are classified into classes based on the cross-section and length of the root neck, which is important because of the knowledge that the crop is larger if the root neck is thicker. There are several classes: excellent A seedlings, superb A+ seedlings and B seedlings which need at least a year to reach full fertility in the bed.
The next category is “Waiting bed” seedlings that can be obtained from green or frigo seedlings. When the seedlings reach the required size, they are removed, cleaned, disinfected and packed in 25 pieces. After that, they are kept in the refrigerator under the same conditions as the frigo seedlings. They must remain in the refrigerator for a minimum of 25 days, and the planting time is planned according to the harvest date, as with container planting.
The last category is container seedlings. The production cycle of container seedlings takes place in a greenhouse and lasts 2 to 3 months. Those seedlings that meet the standards are packed in cardboard boxes and first cooled to +2 ºC and only then to -2 ºC and with a relative air humidity of 95%. They can be stored in this way for five to 10 months.
Strawberry planting time and technique
As the strawberry is a perennial herbaceous plant, it can be planted throughout the year. In intensive one-year plantations, it is recommended to plant strawberry seedlings at the end of July or at the beginning of August, because then the seedlings will produce a safe and high-quality crop in the following growing season.
Planting too early or too late can have a negative impact on the development of plantations and the next year’s crop.
If the soil is not moist enough before planting, it should be soaked abundantly in order to establish a favorable water-air regime. Nowadays, planting is more and more often done with refrigerated seedlings, which after being taken out of the refrigerated warehouse should first be slowly thawed, then moistened and planted in as short a time as possible.
Planting can be done manually or mechanically. If it is done manually, it is planted with a forked planter, which presses the root into the most natural position possible, i.e. to stand upright. It must be pressed into the soil up to the height of the root neck. Whether the seedling will be received or not depends on the regularity of the planting. Therefore, the depth of planting must be taken into account. Neither too shallow nor too deep planting is good because in the first case the root will dry out, while too deep planting will cause slower sprouting and worse acceptance. It is good to press the planted seedling into the soil with your fingers. After planting, it is necessary to water abundantly and maintain humidity for at least another two weeks.
Making beds for planting strawberries
The first bed is made on the prepared plot, which must be level and parallel to the longer side of the plot or road, and the other beds are leveled according to it. The beds are made mechanized, with a connecting machine called a baulator in our country.
The machine works in such a way that two pairs of angled plates grasp and raise the soil and bring it between two metal plates that thus shape the base of the bed, and the roller determines its height by rolling the top of the bed. But today, the preparation of the bed is done with a special machine that simultaneously works the bed, installs drip irrigation pipes and lays a polyethylene (PE) film with a thickness of 0.05 to 0.07 mm over everything. The height of the bed should be between 15 and 25 cm, and the width of the bed depends on the type of PVC film used. For a single-row foil whose width is 120 cm, and the distance between planting places is 20 cm, the width of the top of the bed should be from 30 to 50 cm. For a two-row foil whose width is 130 cm, and the distance between planting places is 30 cm, the width of the top of the bed should be from 40 to 60 cm, which ensures optimal conditions for the development of the root system. The advantages of polyethylene film are multiple from preventing the growth of weeds, it ensures greater purity of fruits and reduces their rotting, it ensures less use of pesticides and accelerates soil heating, i.e. it accelerates ripening and reduces evaporation, which also reduces the number of irrigation sessions. The beds must be formed at least 2 to 3 weeks before planting. There are already drilled planting spots on the polyethylene film, which can be single-row or double-row. If it is a double row, the distances are usually 30 to 35 cm between the rows, and 25 to 30 cm within the row, depending on the lushness of the variety and the fertility of the soil. With such intervals, the density of plantations ranges from 40,000 to 50,000 plants per hectare.
Maintenance of strawberry plantations
Seedlings have developed 2 to 3 leaves 10 to 14 days after planting. At that time, it is easiest to confirm the receipt of the seedlings and carry out the replanting in order to realize the planned assembly.
Along with the development of seedlings, weed plants that develop in the same living conditions must not be forgotten. In addition to preventive treatment before laying the PE film, attention should also be paid to those weeds that sprout from the deeper layers of the soil. These are usually annual grassy or broad-leaved weeds. When they grow up to 5 cm in height, it is necessary to plant them and remove them by weeding. After about 20 days, flower stalks with flowers will develop. They should be removed to enable faster seedling development. In the phase of the most intensive growth, strawberries begin to form boils. Bushes are not desirable, as are flowers, so they are also treated as pests, for the development of which the plant consumes a lot of food. The easiest way to remove ulcers is with scissors.
After the first year, plantation maintenance is reduced to preventing the development of weeds and protection against diseases and pests. Weeds from the planting sites that threaten the bushes are removed by weeding, while those between the rows are controlled chemically. After the end of winter, it is good to clean old, dead leaves and dried heather and remove them from the plastic. This improves the aeration of plantations and prevents moisture retention, which contributes to a better state of health. In the spring, the plantations should be protected again from diseases and pests, and it is advisable to fertilize them as well. In the dry, summer period, it is necessary to irrigate.
Strawberry irrigation
The importance of this agrotechnical measure stems from the property that strawberries, as a fruit species, have a great need for water in all phenophases of growth and development. The water necessary for growing strawberries comes from precipitation in the form of rain, snow and dew and from irrigation.
The problem is the insufficient amount of annual rainfall in certain areas, which is not sufficient for growing strawberries, and the unfavorable distribution of rainfall. For this reason, modern strawberry production is only possible with irrigation.
For example, in a year with average precipitation and average air temperatures, 55 to 150 mm is missing, while in dry years, 90 to 260 mm of water is missing. For this occasion, it was only stated that the established lack of water represents a major limitation for successful and economically justified agricultural production and that therefore the introduction of irrigation as a regular measure in the process of intensive agricultural production is necessary (Bogunović et al., 1998).
Irrigation of strawberries begins immediately after planting. Strawberry is most often irrigated with a drip system.
