ABSTRACT
For the growing of hydroponic vegetable crops start your plants from seed� All seeds have a certain life expectancy called viability� The viability is dependent upon the seed itself as well as age and conditions under which it was stored� To lengthen viability keep the seeds in a refrigerator at about 40°F (4�5-5°C) or slightly higher� Do not put them in the freezer section� In general, large seeds retain their viability longer than small seeds� Lettuce, for example, loses viability after 6 months� As viability falls, so does the percentage germination� This is the percent of seed that will germinate under normal sowing conditions of a moistened medium� Every seed package will give percentage germination at the time of packaging the seed� The date tested is given on the seed package� Tomatoes will retain viability for about 3 years when stored in a cool, dry location� However, the percentage germination will decrease over this time period�
You may test the seed germination quite easily� Put 100 seeds on top of two to three layers of moistened paper towels� Then, cover them with another two to three layers of moistened paper towels� Keep them at about 70°F to 75°F (21-24°C) or whatever germination temperature is recommended on the seed package� Inspect the seed after several days, or after the expected length of time indicated on the seed package for the seed to germinate, and count how many of them have broken the seed coat and started to grow� Take that number of germinated seeds and divide by the total of 100 to get the germination percentage�
This percent of expected germination is important for you to determine how many seeds to sow� For example, if 70% of the seeds germinated, then you know you must sow at least 30% more seeds to get the number of plants you want� As an example, if you want 20 tomato seedlings and you found a 70% germination, then multiply the 20 by the percent you want (100%) and divide by the percentage germination (70%): 20 × 100/70 = 29� Sow 30 seeds to obtain more seedlings than needed� In that way, you can select the most vigorous seedlings to transplant�
Another important factor is to get the best seed available� You may order through many seed distributors such as those listed in the Appendix� The next thing to consider is the choice of variety� In most cases, greenhouse varieties will do best with indoor hydroponics� Do not collect seeds from your plants and volunteer them for the following crop as most varieties are F1 hybrids and will not produce the same plant in the next generation� The choice of varieties is discussed in more detail in Chapter 22�
The form of the plant is also important in your choice� When growing indoors you may use bush varieties, but staking ones are more productive� These are also termed “ indeterminate�” Bush or “determinate” varieties grow to a certain height and then stop, whereas the staking types continue to grow upward� This applies to vine crops like tomatoes, peppers, eggplants, and European cucumbers and not to low-profile crops�
When starting seedlings for hydroponic culture we use a soilless medium� The easiest method of sowing seeds is to use growing cubes� There are many available in the market� If you want to grow in peatlite mixture or coco coir in pots, you may use peat pellets or compact cell trays that you fill with a peatlite or vermiculite substrate� For lettuce, arugula, bok choy, basil, and herbs, it is best to start the seeds in either rockwool or Oasis cubes as shown in Figures 11�3 and 23�8� There are a number of different sizes of these products to choose from� Use the smaller ones, usually 1″ × 1″ × 1½″ rockwool cubes or 1″ × 1″ × 1½″ Oasis “Horticubes” for lettuce, arugula, and so on� With vine crops use the 1½″ × 1½″ × 1½″ rockwool cubes�
When growing vine crops, the seedlings in the rockwool or other cubes are transplanted to rockwool blocks before later placing them in the final growing substrate� The advantage of starting the seed in growing cubes is that you may select the best plants later to be transplanted to the rockwool blocks� This is another reason to sow at least 10% more seeds than the number of plants needed� Growing cubes and blocks must be thoroughly saturated and flushed with raw water prior to sowing or transplanting� Rockwool has a pH between 7 and 8�5 and hence is very basic� Reduce it to optimum levels between 6�0 and 6�5 by using a slightly acid solution after saturating the cubes� This can be done by adding vinegar or acetic acid to water to adjust the pH within this optimum range and soaking the cubes again before sowing the seeds� When preparing the blocks for transplanting, soak them with a half strength nutrient solution having a pH between 6�0 and 6�5�
Rockwool blocks come in various sizes: 3″ × 3″ × 2�5″, 3″ × 3″ × 4″, 4″ × 4″ × 2�5″, and 4″ × 4″ × 3″� The choice of size is a function of the plant grown, the size of the vtransplant, and the stage at which you wish to transplant to the final growing area� The longer the plant is held before the final transplant stage, the larger the block� Place the seedlings in the growing cubes or blocks in plastic mesh trays to permit rapid drainage� The trays should sit on a propagation table of wood or galvanized steel with either wire mesh top or lumber with 1½″ spaces between each cross member� This promotes rapid draining and allows aerial pruning of the plant roots that may grow from the cubes or blocks� Do not allow a root mass to form under the cubes or blocks as damage to the roots will occur during transplanting that will predispose the plants to diseases�
If you wish to contain the drain water from the seedlings after irrigation, build an ebb and flow bench that sits on top of a ¾″ steel square tubing framework, as
described earlier in Chapter 13, Figures 13�2 and 13�3, and Figure 14�1� However, make the dimensions different from those described in Figures 13�2 and 13�3� Make the inside width 49-50″ by 4 ft 2″ or greater in length, depending upon the number of seedling trays, by 3″ deep� Each seedling tray is 1 ft × 2 ft, so a 4 ft × 4 ft bed would fit eight trays� To get complete drainage away from the trays and allow air pruning of roots, place 1″ of igneous rocks in the base of the bed to support the trays above any drainage water (Figure 14�1)� Use rocks of ¾″ diameter� This will give large spaces among them that will dry between irrigations�
Alternatively, make a support frame of 1″ PVC pipe as shown in Figure 14�1� This support frame would keep the mesh trays above the drainage level of the ebb and flow tray� A 2″ high overflow pipe similar to that shown in Figure 13�3 would regulate the maximum solution height at 2″ enabling the solution to moisten the seedlings from below� The overflow pipe, drain pipe, nutrient tank, and plumbing are not shown in Figure 14�1 as they are shown in detail in Figures 13�2 and 13�3� The only difference is that the pump is directly connected to the drain pipe in the bed to fill and drain the bed� Use a 1″ feed/drain pipe from the pump� When the pump shuts off the water will flow back to the nutrient tank below through the pump�
The seedling mesh trays are 12″ × 22″, therefore orient the support frame below so that the trays will be placed perpendicular to the frame� The ebb and flow bed can be 25″ wide by a multiple of 1 ft in length to fit the trays most efficiently� If you need a larger area, make the ebb and flow bench 49″ wide by a multiple of 2 ft (such as 4 ft × 6 ft or 8 ft)� Add an extra 1-2″ to the length to give ample room for the seedling trays� The irrigation cycles are automated with a timer operated pump in the nutrient tank below the bench�
During the initial seeding of the cubes, the cubes could be placed immediately on the surface of the ebb and flow bench, but it is better to use the mesh trays as that allows complete drainage� This method would also be fine for low-profile plants that are not transplanted to rockwool blocks� The placement of the layer of rocks or the
support frame will reduce algae growth in the bottom of the ebb and flow bench due to the exposure to light to a wet surface containing nutrients�
When using the ebb and flow system for the rockwool blocks, keep them in mesh trays and cover the surface of the bed with rock or something else to prevent algae growth� Several layers of black nursery weed matting on top of the rock layer will further discourage algae growth�
Specific details of sowing and transplanting for each crop are given in Chapter 23�
