Methods of maintaining a growth head start in vegetable transplants

"Head start" is the earlier growth and development of plants grown from transplants compared to plants grown via direct sowing. It is closely related to the age of transplants. Therefore, before considering the features of the "head start" manifestation, it is necessary to clarify the concept of "transplant age".

It can be expressed in the following ways:

• in days during which the transplants were grown;
• by the number of leaves;
• by the developmental stage;
• by the state of development of reproductive organs.

Characterizing transplants by the number of leaves or their developmental stage reflects the age more accurately. For example, if you grow tomato transplants in March-April, they will form six to eight leaves in 50 days, but if grown in January-February, it takes 75-80 days, as lighting conditions and temperature regimes differ in facilities used for growing transplants during winter and spring periods. Therefore, when transplant age is indicated in days, which is generally accepted, it is necessary to specify the growing duration or indicate the number of leaves on the plant.

"Head start," if expressed in days, is always less than the transplant age, since when selecting transplants for planting in the field, part of the root system is lost, and the growth of stems and leaves is suspended during the recovery period. Sometimes, even the withering and drying of lower leaves is observed. This is likely due to the outflow of plastic substances to the roots, which have lost their entire absorbing surface during transplanting. It also plays a role that transplants grown in greenhouses and hotbeds are less adapted to natural light and sharp temperature fluctuations compared to plants formed in open soil, and time is required for their adaptation to these conditions. Considering all this, the "head start" is not determined at the time of transplanting, but by the calendar dates of the beginning of the harvest for the compared transplanted and direct-sown plants.

Reducing the loss of "head start" using the transplant method of cultivation is one of the important concerns for vegetable growers. Each type of vegetable plant tolerates transplanting differently, and this factor should be considered when choosing the method and conditions for growing transplants. However, there is a pattern characteristic of all vegetable crops that is important when solving the problem of maintaining the "head start" in the growth and development of plants grown from transplants: the younger the plant, the faster it takes root during transplanting and the less "head start" it loses. But at an excessively young age, it is impossible to create a significant "head start." At the same time, older transplants lose a lot of "head start" during transplanting, which may not justify the costs of growing them.

Therefore, for each vegetable crop, an optimal transplant age is determined, when the plant has not yet lost the ability to relatively quickly restore the root system partially lost during transplanting, while at the same time allowing for a sufficiently large "head start" in growth and development that is economically feasible.

It is necessary to note one more pattern that is important for the problem under consideration. If the roots of a transplanted plant are fully preserved, it will take root quickly even during the fruiting period. Consequently, avoiding a large loss of "head start" is possible by selecting a transplant-growing method that maximally preserves the roots when picking them for planting in open soil. Such methods exist and have long been used in vegetable farming — growing transplants in nutrient cubes, pots, peat slabs, cups (paper, peat, plastic) filled with a special nutrient mixture; and in recent years, cell trays and blocks filled with various substrates are already being practiced.

Previously, cubes or squares cut from turf soil were used for these purposes. Transplants grown in such conditions are planted in the soil along with the nutrient cubes (pot, cup) or along with the nutrient mixture if the containers are plastic. In this way, it is possible to preserve up to 80-90% of the formed roots. Sometimes, if it is impossible to use pots, cubes, or special containers, growers resort to picking and planting transplants with a clod of nutrient soil or earth. In this case, more than half of the roots will be preserved during transplanting if the feeding area of the transplants is slightly increased compared to the accepted standard of planting density. In the case of non-pot transplant cultivation, very abundant irrigation before picking contributes to root preservation, as it strongly liquefies the soil, from which the roots are easily extracted.

It should also be noted that excessive density of the grown transplants always negatively affects their survival in the open soil and leads to a large loss of the "head start". This is the result of insufficient light and limited development of the root system due to a small feeding area for each plant.

Reducing the loss of the "head start" of transplant crops is facilitated by a system of techniques for preparing transplants for planting in the open soil, which is called hardening in vegetable growing practice. Its essence lies in ensuring that the plants gradually adapt to the conditions of the open soil. The parameters of the conditions for transplants during this period are described in the section "Preparing transplants for planting in the open soil".

Protecting transplants from the sun and wind during transport

When transporting transplants to the planting site, plants are easily dried out or damaged. Direct sunlight and dry wind quickly deprive the fragile seedlings of moisture, which negates the accumulated head start in growth. To preserve the potential of the plants, protect them from stress factors throughout the journey from the greenhouse to the furrow.

Various materials are used to protect the transplants, allowing for shading or fully covering the plants. Protective covers are essential at two key stages:

• directly in transport vehicles during transit;
• at temporary storage sites for transplants at the edge of the field before planting.