Growing Your Own Hydroponic Transplants (Part 1)

Introduction

There are many ways of raising healthy transplants for establishment into a hydroponic system, and often the method used will depend on the crop being produced, the system used and the grower’s personal preference. Very few hydroponic crops are direct seeded, so being aware of the range of propagation options and how these eventually affect plant establishment rates becomes important for healthy crops. Some crops such as strawberries, tuberous plants like sweet potatoes and ornamental cuttings need special care and attention for successful establishment while various hydroponic systems need methods which will support the young plants until the root system has fully developed. Whichever method is used to successfully establish young plants in a hydroponic system, care of the root system and preventing tissue damage is vital and learning to recognise the symptoms of rough handling becomes important for all growers.

Raising your own transplants for quick establishment

Starting your own plants from seed or cuttings is one way of ensuring they are ready at just the right stage for rapid establishment into your hydroponic system. This is also a good way for growers who are just starting out or experimenting with hydroponics to trial different methods of plant raising and crop establishment which will best suit their particular system. The cost of raising transplants is also important in most hydroponic operations and often establishment rates for plants raised in an inexpensive propagation system will be just as good as those which utilise expensive custom made equipment and materials. Establishment success and rate of plant development after planting are highly dependent on the health of the seedling being introduced to the system, and this is often more important than the system used to raise the young plants in the first place.

Pots, containers, cubes, bags, blocks, cells and trays

The range of pots, containers, cubes, bags, blocks, cells and trays available to raise transplants for establishment into hydroponic systems is endless. There is also a fairly varied selection of suitable media which can be used to surround the developing root system, so the combinations can be confusing as to which will give a crop the best start possible. Rockwool and oasis cubes tend to come in standardised sizes and are widely used by both commercial and hobbyist growers. With rockwool, care needs to be taken not to overwater or have the cubes siting in any depth of water or nutrient as this media holds large volume of moisture which can retard seedling development. Oasis, depending on the type and quality, does have a tendency to become dry on top and overly damp on the base if the irrigation is not well monitored and controlled. Both oasis and rockwool however, are sterile and allow maximum root outgrowth without any restriction when planted into any hydroponic system.

Compressed disks of coconut fibre or peat (Jiffy 7’s) are also popular with growers of crops such as tomatoes, cucumbers and peppers. The compressed disks are soaked in water for a few hours, to make the media expand and swell out ready for planting. The media his held within a fine net bag, which doesn’t restrict root outgrowth and these small media disks can be later planted out into NFT or media based systems, where moisture is held by the media around the root system until the plant is established enough to develop roots out into the NFT channels.

There are also many small plastic pots - both rigid and thin walled which can be used to grow transplants for later crop establishment.

Thin walled disposable pots which come in sheets to later be separated into individual pots at planting time, are widely used by lettuce and herb growers. These pots (or ‘cups’) are left on the root system when the entire lettuce or herb is harvested with the root intact and this acts as a moisture reserve during shipping and marketing. Cell trays are still used by some growers since they come in a wide range of sizes and are cost effective. Small plastic planter bags are sometimes used to establish larger fruiting plants which are later transplanted into larger containers or media beds in a hydroponic system.

Recycled containers for raising transplants

Hobbyist growers are usually fairly innovative when it comes to recycling containers to raise plants and there are a number of ‘food grade’ plastic containers which can be put to use in a hydroponic system. Small yoghurt pots with large holes drilled or cut into the base make ideal containers for raising seedlings for NFT systems. Small waxed milk or cream cartons can be used to raise larger plants, particularly those such as fruiting plants which may take some time to propagate from cuttings. So long as the plastic is ‘food grade’ it will be safe to use to grow plants, however most of these containers don’t have the UV inhibitors that many plant pots do and eventually break down in sunlight.

Biodegradable or reusable pots for hydroponics

More growers these days are becoming interested in ‘organic’ production methods using hydroponics and recycled and biodegradable materials for plant propagation are thus becoming popular. Hobbyist growers may prefer to invest in thick walled, UV resistant plastic containers to raise their seedlings in for their hydroponic system - these can later be removed from the plant’s root system at harvest, cleaned and reused as a cost effective way of getting good establishment rates from their plants. However biodegradable materials such as card and paper also work well in hydroponics and can be incorporated into just about any type of system. Paper pots, filled with media such as perlite/vermiculite, expanded clay, sphagnum moss, pumice sand or coconut fibre can be used for just about any type of seedling or cutting and have the advantage of being cost effective to make out of waste paper. These type of pots also prevent any root damage from occurring during transplanting, and will rapidly disintegrate and break down once the roots push through the pot.

Bare root transplants

Where large numbers of plants need to be raised in a small space, direct sowing into trays for later ‘pricking out’ and then bare rooting into a hydroponic system can work well for certain plant species which will tolerate some root damage. Many vegetables such as cabbages, cauliflower, broccoli, tomatoes, pepper and many ornamental plants will tolerate this type of propagation system. Selecting a media which is highly friable is important for this process, so that as little of the propagation media as possible ends up in NFT systems. Timing is also important with bare root transplants, if these are left in their trays for too long, the roots will intertwine, making separation difficult and resulting in more root damage during the preparation for transplanting. Care also needs to be taken to ensure that the root system never dries out during planting out our during the establishment period as the roots don’t have any reserve of moisture.

Buying in transplants

Many commercial growers don’t actually raise their own transplants but have them produced by a specialist nursery and delivered when they are required. These transplants tend to be raised in sterile inert media, rockwool cubes or what ever the grower requires and a good nursery will provide healthy transplants which establish rapidly into the final system. However, hobbyist growers are often faced with a newly cleaned out hydroponic system and no seedlings ready to go in it. In this case, establishing seedlings can still be carried using normal cell transplants as these are usually raised in a ‘soilless’ potting mix or sold bare rooted, wrapped in damp sawdust or paper. Wherever possible avoid buying seedlings which appear to have soil attached to the roots or soil contamination on the foliage or in the growing media - you don’t know what other pest and diseases problems might be coming along with your new plants. Seedlings in small cell trays of potting mix can be gently removed and placed straight into most hydroponic media beds after shaking off any loose media. The fertiliser contained within the media surrounding the roots is usually such a small volume it will not upset the hydroponic nutrients. For transplanting in NFT systems, its not a good idea to completely remove and submerge the root system in cold water in an attempt to wash off every speck of potting media­–this will end up causing extensive damage to the roots and has been known to result in slow establishment rates. Shaking off as much loose media as possible and then placing the root ball in the NFT system (or into a small plastic pot which is sitting in the NFT system) will give a much better establishment rate with out overly damaging the root system or stressing the plant. Installing a filter at the end of the channel or on the return pipe will catch any particles of the potting mix which may float away from the root system.

Establishment problems and rates

Many hydroponic growers have experienced problems with getting good establishment rates in their system from time to time, however plant survival rates are usually considerably higher in hydroponic systems than they are with transplants out in the field. Most establishment failures tend to be caused by either damage to the plant during handling, with later secondary infection by pathogens such as pythium, or by a problem within the plant’s new environment, making adjustments to the new system difficult. The most important point to remember about plant establishment is to handle young seedlings with care, avoid root breakages where ever possible and either ‘harden off’ your seedlings or modify the new environment (or both) to assist the plant to adjust. Young, vigorous and soft seedlings which have been raised in a warm greenhouse with some shade and plenty of moisture will suffer a check if suddenly planted in an outdoor system in full sun, although most plants will eventually recover, some losses could be expected. Hardening off of transplants is important in many crops, but soft, succulent lettuce, greens and herbs can be severely affected. Soon after germination, seedlings should be gradually exposed to the conditions they will experience in the final hydroponic system so that temperature, light, moisture and nutrient levels will be similar during the final stages of propagation and when finally planted out. Nutrient EC is usually applied at a low (half normal strength) rate during the early stages of propagation, but should be gradually increased so that the young seedlings do not experience any ‘EC or osmotic shock’ during the establishment period.

Handling damage

Young transplants need to be handled with care, although it is usually impossible to avoid all root disturbance. Bare root transplants in particularly suffer considerable root damage when pulled from the media and separated from each other, and this method should only be used on plants which will recover and regenerate roots fairly quickly. Bare root transplants can be used for small seedling of tomatoes, peppers, lettuce and some herbs. Small Root breakage’s are not so much a problem for plants as these can be regenerated, but they provide an area of dead tissue which can be rapidly infected by root pathogens such as pythium. Large areas of damaged root system however make it difficult for the plant to take up sufficient moisture to establish strongly in the final hydroponic system and any plants which end up badly damaged should not be planted out.

A second type of handling damage that can result in plant losses during the establishment period is ‘stem constriction’ or stem ‘squishing’ which is actually a lot more common than many growers realise. The first signs of this do not appear for several days after transplanting and are often mistaken for a disease. The stem may appear water soaked or translucent - usually about half way up the plant and eventually the tissue collapses and the plant topples over This physical damage is caused by crushing or bruising of the sensitive stem area during handling and planting out into the hydroponic system. Young transplants and seedlings should never be handled, picked up or grasped around the stem area - they should only be handled by the propagation cube or pot or in the case of bare root transplants by gently gripping the largest leaf. Larger bare roots seedlings such as tomatoes, can be gently grasped at the top of the root system.

Root Restriction and Root Bound Seedlings

A lesser encountered problem with ‘slow’ crop establishment is when the seedlings or young plants have been held too long in the propagation area and have become ‘root bound’. While most plants will eventually regenerate new roots out into the new hydroponic system, being root bound does slow the plants development and establishment. Where seedlings need to be held for longer than usual a larger sized pot, container or propagation cube should be used so that the roots have sufficient room for development before they are planted out.

Reasons for slow establishment or root death after planting out

Generally, if the seedlings are healthy and environmental conditions are suitable, plants will establish rapidly when planted out into a hydroponic system. New roots should be visible growing out from the transplant within a few days, however slow establishment does occur and can have many causes. The most common cause was root damage during transplanting, the greater the damage to the root system, the longer it will take for the plants to fully establish in the system. However, sometimes there are other causes for slow crop establishment in hydroponics, these include pathogen pressure in the new system, water logging, temperatures which are too hot or cold, pests such as fungus gnat larvae, incorrect EC levels, salinity damage and any other problem within the nutrient solution which affects plant growth.

Pathogens, of which Pythium is the most common, can be present in seedlings or in the water supply in many hydroponic operations and can be the cause of slow crop establishment even without their being any visible signs of diseases in the root system. Pythium and other root pathogen infection can be common in newly planted crops as seedlings are at a venerable stage after transplanting when root damage is likely to have occurred. If pythium is suspected, growers can use a ‘do-it-yourself’ pathogen test kit to get quick and accurate confirmation if this is the problem. Otherwise running checks on nutrient and root zone temperatures with a maximum/minimum thermometer, checking EC, pH, keeping a close eye out for insects such as fungus gnat larvae around and in the root zone and using a good nutrient formula will prevent most problems of slow establishment from occurring. In NFT, nutrient stagnation and a flow which is too deep resulting in water logging can be a common cause of slow crop establishment and transplant deaths. Another common problem can be the growth of algae in NFT systems which smothers the root system and slows root growth. Algal growth can be prevented by making the gullies as light proof as possible, even if this means painting the outer surface of thin walled channels to prevent light penetration into the root zone. If light is entering through the planting holes where the young seedlings have been placed, a ‘collar’ of black and white panda film or light proof plastic can be easily made and slipped around the stem of the young plant to prevent light falling into the channel and resulting in algae growth on the developing root system.

Summary:

Crop establishment into a hydroponic system should be a straight forward and rapid process provided the steps carried out to produce healthy transplants and prevent root damage are carried out. Crop monitoring and maintaining a suitable environment after planting will usually result in a high success rate with transplants. Many growers will develop their preferred method of raising transplants for rapid establishment into their hydroponic system, but experimenting with the many types of crop establishment methods, media and materials is a good way of determining what will give you the best plant growth in your particular type of system. Watching a young plant stretch out its roots into a hydroponic system and rapidly shoot away is the ultimate reward from successful crop establishment.

In part two of this article series, raising transplants of a number of different plant species for establishment into different types of hydroponic systems will be covered.