Growing Your Own Hydroponic Transplants (Part 2)

Introduction

In part one of this series, the basics of raising your own seedlings in different pots, containers, bags, trays, cubes and media for planting out into a hydroponic system was outlined. In this article, the specifics of raising seedlings and cuttings destined for different growing systems is covered, along with details of some different hydroponic crops and how they should be prepared before planting out. Some commonly grown plants are hardier than others and can be bare rooted into hydroponic systems with very little set back, while others are more temperamental and need to be raised in their own ‘cell’ of media so that root damage is prevented at planting out time.

Preparing transplants for different systems

NFT Systems

NFT (nutrient film technique systems) which don’t utilise any solid media often cause the most concern for growers over how they are going to establish and support young seedlings or cuttings while they develop a new root system. Luckily, the manufacturers of many NFT systems have designed various ways of plant support including solid and net pots, various disposable pots, media cubes, disks and tubes all of which can be used to raise young seedlings which are then simply slotted into the NFT channels at planting. Opinions over which method works the best are varied - some growers prefer to use a media which does not restrict root outgrowth into the NFT channel such as small oasis or rockwool cubes, compressed peat to coconut fibre disks which swell up in water, and paper pots which dissolve and disappear once planted into the NFT system. Other growers use plastic pots which are washed and sterilised and reused as part of the system or thin walled disposal plastic pots with holes in the base to allow root outgrowth into the NFT channels. Larger plants can be ‘bare rooted’ into small NFT channels, but often have the problem of slipping down into the channel with the flow of nutrient if sufficient support is not provided.

Capillary Matting

One of the most important aspects of crop establishment in NFT gullies or channels is distribution of the nutrient flow along the base of the channel. With flat bottomed channels, the nutrient in an empty system will not flow evenly in a thin film over the entire surface of the channel, but will meander in a stream which may not make contact with the base of the transplant or pot when few roots have grown out into the system. This problem is easily correctly by laying a thin capillary or paper ‘mat’ down the surface of the channel before placing any new plants in the system. The mat will wick nutrient along the surface of the channel so that each new transplant will receive moisture - the plant’s roots will rapidly grow out and into the nutrient flow, so a capillary matting or cloth/paper material which dissolves after a few weeks is often used. Many of the newly designed NFT channels on the market these days have solved this problem by having pre moulded grooves or small channels that spread the flow of nutrient along the base, so that the addition of capillary matting is not required.

Media Based Systems

Crop establishment into media systems is fairly straightforward in most cases. Rockwool based systems using grow slabs and propagation cubes work extremely well together, however the transplants are not ready for planting out until they have visible roots on the underside of the propagation cube. The reason for this is that these roots will be used to anchor the plant and the propagation cube to the grow slab, giving the plant some support until it is trained to overhead strings or wires. It normally only takes two to three days before these seedling roots have grown down into the grow slab and are giving the plant extra support.

In media beds, transplants will establish fastest if they are planted at the correct depth - too deep and the stem could rot in overly damp conditions and if not deep enough, the plant won’t have the support it needs for rapid establishment and the root system can suffer drying out.

Flood and Drain Systems

Flood and drain systems usually incorporate some form of media to support the young plants and hold sufficient moisture during the ‘drain’ cycle, however establishment success depends largely on getting the frequency of the ‘flood’ cycles adjusted for the stage of plant development. While the young plants are establishing, they have a limited root mass extending out into the media which can extract moisture and nutrients, so short, frequent flood cycles will give good establishment rates, provided the media is not left overly saturated between irrigations. If the media dries out between waterings, establishment rates will suffer and plant losses will likely occur.

Floating or Raft Systems

Floating, raft or pond type systems are well suited to using small cubes of media such as oasis or rockwool which can be wedged into the floats or rafts and will support the young seedling, providing moisture until the root system has fully extended down into the nutrient pool. However, small pots or plastic tubes are also used in some systems to extend the young plants root system down into the nutrient. This is particularly beneficial where the raft system has an ‘air gap’ between the base of the raft and the nutrient. Larger plants are sometimes bare rooted into floating systems where they have developed a root system which will extend well down into the nutrient pond when planted.

Aeroponics

Aeroponic systems have been designed which use a wide range of establishment methods, the most common being small plastic ‘net’ or ‘lattice’ pots which are filled with a small volume of inert media in which the seedling or plant is raised. Once large enough, the net pot is slotted into the top of the aeroponic system and the nutrient mist keeps the media moist until the roots grow out and down into the misting chamber. Net pots allow maximum misting of the young roots system and good root outgrowth in to the chamber. Rockwool, oasis and bare root transplants are also used in some aeroponic systems with good success.

Specific Crops

Tomatoes, Peppers, Cucumbers, Egg Plants and other large, long term crops

Probably the most common plants grown in hydroponics are those which are large enough and valuable enough to warrant individual attention. Luckily these type of plants transplant well and are fairly tolerant of a wide range of establishment methods used for hydroponic production. Many commercial growers will have their favoured method of crop establishment for these fruiting plants, based on past experience, the type of system they are using and the cost of production of the transplants. Generally tomatoes, peppers, cucumbers and egg plants are not direct seeded where they are to grow, but raised away from the production system in special nursery areas - this system however makes successful plant establishment essential, as the young plants must adapt from the protected seedling environment to the new growing area and some degree of ‘hardening off’ is usually required.

The most commonly used methods of raising tomatoes, peppers, cucumbers, and egg plants for rapid crop establishment into hydroponics is with individual pots or rockwool cubes. Some growers may use compressed disks of coconut fibre or peat if these are compatible with their production system. Rockwool systems involve sowing the seed directly into small propagation cubes of 2 - 3 cm in diameter. Later, as the seedling develops its first true leaves these propagation blocks are separated and each is placed inside a larger rockwool cube which will support seedling growth until the plants are ready for their final transplanting. Each step in this process ensures that the seedlings are not overly disturbed and that the root system is not damaged, and using this method, plant losses resulting from root damage during transplanting are generally very low. The rockwool propagation cube with the young plant allows transplanting into the hydroponic system at a much later stage than would be normal with cell transplant raised seedlings, as the individual cubes can receive nutrient and be spaced to allow good light interception by the seedlings. Many growers will hold tomato seedlings until flowering of the fruit truss before transplanting out if rockwool cubes are used.

Establishment of these crops into the production system is relatively simple, however this process should not be carried out until the root system of the young plant is well established in the propagation container or cube, although certainly not root-bound. A profusion of fine white roots should fill the container, and be ready to establish vigorously into the growing media or nutrient solution of the crop’s growing system. Roots should be visible, protruding slightly from the base of Rockwool propagation blocks.

Lettuce Salad Greens and Herbs

Smaller plants such as lettuces, salad greens, herbs and other vegetables can also be directly sown in hydroponic systems, but under commercial production, they are usually grown in separate areas until they reach an acceptable size for transplanting into the production system. There are a few exceptions with some of the herbs such as cilantro (coriander), dill and fennel, which can certainly be transplanted with care, but many growers will chose to direct seed these plants into media beds and establishment rates after transplanting are often slow.

In commercial systems, growers commonly use either small, thin walled disposable pots or cubes of inert media such as oasis or rockwool to raise large numbers of lettuce, greens and herb seedlings for rapid establishment. Some growers however do successfully establish bare root plants into NFT and media beds. Other lesser used methods of establishment include paper pots filled with inert sterilised media, reusable plastic pots for NFT, and compressed disks of coconut fibre or peat.

Strawberry Crop Establishment

Strawberries sometimes prove to be one of the more challenging crops or plants to establish in hydroponics simply because they are not usually raised from seed in inert media so new plants need to be purchased as ‘runners’. Buying in pre chilled runners in bulk from a strawberry propagator means the plants will probably have been grown and propagated in soil in the field and will require some extra attention before they can be transplanted into a hydroponic system. Hobbyist growers can purchase strawberry runners in garden centres, and these are usually sold wrapped in bundles of 10 - 20 plants in a dormant state with no leaves and only a few dried roots. The actual strawberry ‘crown’ is where the new leaves and roots will originate when the plant is given moisture and warm temperatures to regenerate. However, when obtaining strawberry plants in this way for transplanting into a hydroponic system, check to see the plants are still viable, if kept for too long in this state, the crown can dry out and the plant will die resulting in a lack of plant regeneration. Strawberry runners should have a plump crown, with some green visible in the centre - don’t be concerned if old dead leaves are still attached or a large dried root system, these will be cut off and new growth will be produced from the crown of the plant.

For strawberry plants destined for NFT systems, initially raising the plants in small plastic pots of sterile media means the crowns can be placed at just the correct depth. Bare rooting runners into an NFT system can be done, but generally the crowns have a habit of slipping down into the gully or channels and becoming water logged, resulting in rotting and plant losses. Strawberry crowns need to be planted just above the level of the media with only the base of the crown, where the new roots will emerge, under the media surface. The crown is then less susceptible to rotting or pathogen infection and a tuft of new leaves will rapidly develop. Any plants which show no signs of bud break and new foliage should be removed and disposed off to prevent fungal diseases from spreading to the healthy plants..

Once new roots are seen emerging from the base of the individual plastic pots the strawberry plants can be transplanted into NFT systems. Using the correct size pot is essential at this stage, as the crown of the plants needs to be level or above the surface of the NFT channels or gullies. This ensures air movement can be maintained around the base of the plant where humidity levels can become high and pathogens can cause problems. The new roots should be in contact with the base of the gully and will then wick up nutrient to the plant via capillary action. Using pots or ‘plastic tubes’ with sufficient holes at the base is also vital for strawberries which produce a large and fibrous root system at maturity. At this stage, plants can be removed from the plastic pots and placed into NFT systems provided care is taken to keep the crowns above the level of the gullies, so often some form of plant support is required to do this. Plants that have been initially sprouted in trays of media can then be planted into media based beds in hydroponic systems or larger containers in drain to waste or flood and drain type systems.

Once you have your own crop of hydroponic strawberry plants, establishment and propagation of more plants is a simple matter - runners can be removed from mature plants and rooted in a free draining media or left to root around the mother plant and later cut and dug up for transplanting elsewhere. These pre-rooted runners can also be chilled for out of season production of another strawberry crop.

Sometimes, smaller growers want to be able to transplant and establish mature strawberry plants into their hydroponic system which are already pre-rooted in pots or the garden. In this case, the root system needs to be fully washed to remove the media/soil and the tops trimmed back to assist with establishment into the new environment. For plants which have been raised in a potting mix or inert media this is usually a simple task. For plants which are being removed from soil to go into a hydroponic system, (which we are usually told should never be done, but most of us do it anyway!), as much soil as possible needs to be washed off - the root system should then have a quick dunk in a fungicide solution before planting into hydroponics. The reason being, that soil itself is not the problem in hydroponics (a good filter will pick up any grit in the system), but the potential pathogens, insects, and nematodes which can come with the soil are. On the other hand, many of us have successfully established plants from soil into our hydroponic systems with no real problems.

Flower and Ornamental Crops

Depending on the particular flower species, crop establishment into hydroponics for most cut flower plants is relatively simple. Commercial growers will usually either raise seedlings themselves or buy in pre-rooted cuttings or young grafted plants such as carnations, roses, and chrysanthemums. Many flower seedlings are grown in large quantities in cell trays so the individual cells can be easily transplanted into media based hydroponic systems with very little disturbance to the root system. This means hydroponic flower growers can purchase seedlings or cuttings from nurseries who mainly produce plants for soil based growers, since these are raised in inert media or potting mix which is compatible which most hydroponic media or substrates used. NFT flower growers don’t often bare root in small seedlings to their channels or gullies, but use small disposable plastic pots, or plants raised in rockwool or oasis cubes. Larger, cutting grown plants which have developed a root ball of sufficient size - such as carnations or chrysanthemum can be bare rooted into NFT systems as the plants are usually supported with flower netting or stakes.

Cut flower crops which are grown from bulbs, tubers corms or rhizomes are traditionally grown in media based hydroponic systems, although they can also be produced in NFT. Flower plants which are propagated vegetatively by these means are usually fairly simple to establish in hydroponics, provided care is taken not to waterlogg the media during the critical stages of establishment. Flowering plants which are established or propagated by these means are Dahlias, Calla lilies (Zantadescia) and Sandersonia each of which have their own special requirements for propagation, growth and development under commercial production. Smaller growers who want to establish a few of these types of plants in a small hydroponic system are best to raise the tubes, corms or bulbs initially in small containers of media, away from the final growing area, for later placement into the NFT system or young plants transplanted into the final media system. This means any tubers, corms or bulbs which have not sprouted and produced a healthy root system and new leaves can be discarded, rather than left to rot in the hydroponic system where they would cause disease problems.

Root Crops

Establishment of root crops into hydroponic systems is not difficult, but since root crops such as carrots, radishes, parsnip, potatoes, sweet potato, yams and some of the more unusual root crops are not grown commercially on a large scale in hydroponics, hobbyist growers are often at a loss as to how to achieve this. Root crops can be grown in media beds, drain to waste systems, NFT, aeroponics and even floating systems if the right support is provided and the root or tubers being produced have sufficient room for development. The simplest systems are large, fairly shallow media beds with just enough depth for root development of the crop. Seeds are sown direct onto the surface of the media bed, and later the seedlings are thinned to the correct spacing. This works particularly well for baby carrots, turnip, radish and similar small root crops. The plants don’t suffer any root check which transplanting would cause and develop with a good root shape. Larger root crops such as potato, sweet potato and yams can be grown in the same way in media beds with pre-sprouted tubers planted directly into the media, but these types of plants have also been successfully grown in NFT channels, aeroponics and other systems. Media-less systems do have the advantage that the grower can easily view the processes of root growth and tuber development, deciding actually at which size and stage the crop is harvested as in the case of baby potato production. Small seed potatoes, can be pre-sprouted before planting into hydroponic systems, and in NFT the tubers can either be supported by a cube of rockwool, which allows maximum root outgrowth, and simply placed on capillary matting inside the channel or gully.

Establishment of Older or Mature Plants

Hydroponic growers are sometimes faced with moving or transplanting a mature plant into another system or position. Depending on the plant species, this is usually successful, provided the root system is not overly damaged and the new position is suitable. Getting a mature plant with an extensive root system out of an NFT gully can be a challenge which involves a get deal of root trimming, however removing or ‘re-potting’ a media grown plant is more likely to be successful. Perennial plants such as chives, garlic chives, lemon grass and a few other herbs actually benefit from being pulled out, divided and replanted when mature and will re-establish very quickly. Plants which are carrying a heavy fruit load, such as tomatoes will generally not re-establish well as the plant will continue to put all its energy into fruit production, rather than producing new roots when shifted into a new position.

Summary

Successful establishment of seedlings, cuttings or even larger mature plants into a hydroponic system is a vital step that growers need to master. There is nothing more disappointing than having young transplants fail to ‘take’ in their new growing environment and system, so taking a little time to plan and raise seedlings and cuttings correctly goes a long way to successful establishment after plant out. Using the method of seedling or plant raising most suited to the crop type and the hydroponic system in use is an important combination and sometimes it takes some trial and error to determine the best way of preparing young plants for different growing situations.The first few days after transplanting out a young plant into a new growing system are the most important and keeping a close watch on the plant’s health and root development are a good idea as establishment problems will soon make themselves known. Healthy transplants, rapidly established in a well maintained hydroponic system are important to get good growth rates, high yields and top quality plants that growers enjoy.