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Frequently Asked Questions


What is hydroponics?

Hydroponics is the science of growing plants without soil. The plants thrive on the nutrient-water solution alone.  The growing medium merely acts as a support for the plants and their root systems while the solution passes freely. The growing medium, if any, is totally inert.

What are the advantages of hydroponics versus growing plants in soil?
You can grow more plants per square foot in a hydroponic garden because roots are directly fed ~ therefore, there is no competition for root space. As a result, you can get higher yields per square foot, per unit of time. Your plants will grow faster because they will be getting all the nutrients they need and in the proper proportions. Their root systems stay smaller, so the plant can concentrate it’s grown energy on producing plant mass, rather than roots.

Isn't hydroponic gardening complicated?
NO! If you follow directions, you can garden hydroponically. A few simple steps must be followed on a regular basis to ensure that your plants thrive. Once you get used to the routine ~ it’s a snap.

Can I grow organic plants hydroponically?
Organic and hydroponic growers have typically regarded each other somewhat suspiciously and the two growing methods were not thought to be compatible. There is common ground, however, and more people are finding that with a little experimentation, they can grow a successful organic, hydroponic garden.  Products used for hydroponic gardening include bat guanos, liquefied seaweed products, fish based fertilizers, and an extensive line of organic nutrients, such as General Hydroponics Organics. Ask us for more information on organic, hydroponic gardening.

What types of plants grow best hydroponically?
Anything can be grown hydroponically, but some plants prove to be more space efficient. Some plants we suggest are tomatoes, sweet peppers, hot chilies, lettuce, spinach, squash, cucumbers, broccoli, beans, snow peas, herbs and flowers of all types.

Can you REALLY get better yields/quicker growth in less time?
Absolutely. The plants, receiving everything they need, tend to be healthier, faster growing and generally more productive. Expect 30% faster growth with many crops.

What about taste? How will the flavor compare to my outdoor grown, organic produce?
You bet ~ perhaps even better! This is simply due to the fact that the hydroponically grown plants are getting everything they need, when they need it. Don’t be fooled by “hot house” produce grown commercially. The grower’s primary concern is shipability and storage, not flavor. When you grow your own vegetables at home, you can expect nothing less than excellent results. Plus, hydroponically grown produce has the added benefit of a longer shelf life.

What is the best growing medium?
There is no clear cut answer to this question. Like everything else, this comes down to preference. Different mediums work better for different situations and different crops.
Rockwool will allow the grower an easy set up, since it is pre-formed and modular. It holds a tremendous amount of water and offers a buffer against drying in the case of electrical outages or pump failures. As Rockwool is disposable, it lends itself to quick end of crop clean-up. Also good for starting seedlings and cuttings.
Coconut Fiber is recently becoming more popular. Coconut fiber is the first “organic” medium to offer high performance in modern hydroponic applications. It can also be added into soil mixtures to increase water retention. Coconut fiber holds more oxygen than rockwool and is pH neutral.
Grow Rocks (Called ViaStone or Diatomite) are a super-fired type of baked clay formed to create a porous, reusable hydroponic media. Due to their sturdy nature, Grow rocks provide secure support for the plants’ root zone. This non-degradable, sterile growing medium provides the delicate balance between moisture retention and aeration and holds a neutral pH. Easy to use.

How do I know how much growing media I need?
For the media capacities of various sizes of containers as well as many other helpful charts, please see our Measurement Conversions page.

Why do I need to test pH? How do I test pH?
pH has a range from 0 (acidic) – 7 (neutral) – 14 (alkaline). A proper hydroponic pH range is between 5.5 to 6.2 for most hydroponic crops - for specific crop pH, visit our Plant Guide. pH must remain within the proper range for good plant health, disease resistance, and proper nutrient uptake. pH is maintained by adding pH Up and pH Down to the nutrient solution. For more information, see the Tests section of our site.

What are the watering cycle timelines for various hydroponic systems?
Once the reservoir is filled with nutrients, it is time to put your hydro system to work! The ease of hydroponics is automation - automation is achieved by putting the submersible water pump on a timer according to your watering needs. The watering cycle depends on growth stage, growing medium and hydroponic system. In an ebb and flow or drip system with rockwool as the medium, seedlings, clones and plants in the early vegetative stage require watering only once a day for 15-30 minutes (twice a day for higher temps). Mature, flowering and fruiting plants require a heavier feed and can be fed once a day for 30 minutes (twice a day for higher temps).

ViaStone, Hydroton, Grow Rocks, and Silicate mediums need to be watered more frequently - a constant drip for drip systems, and about 15-30 minutes every 3 hours for ebb and flow systems and can be adjusted for heavier feeding during the flowering and fruiting stage or higher temps.

Aeroponic systems require frequent watering cycles; 30-60 seconds every few minutes or a constant spray.

How often should I change my hydroponic reservoir?
Nutrient solution uptake will be determined by the type of crop being grown and how heavily they are feeding and the temperature of the grow room (the higher the temp, the more the plants will feed.) It is extremely important that you have a TDS meter and a pH meter and that regular testing on the nutrient solution is carried out.
If you follow a nutrient line's feed schedule, they will typically have it based on changing out the reservoir every week. Topping off with nutrients and water is possible, just be sure to do the proper math and use your meters to prevent over or under watering.
Do I need to use Reverse Osmosis (RO) water?
Nutrient manufacturer’s feed charts require using 0 PPM  (parts per million) water as a starting base for the nutrient solution. A 0 PPM base is achieved with the aid of an RO system. All tap water has natural salts, free chlorine, chloramines and other contaminants so it is often more difficult to adjust the PPM’s of your nutrient solution. It is helpful to know your water. Water test kits can be ordered online and are quick and affordable. Water hardness can often cause deficiencies, imbalances, and and lockouts. It is often advised that organic gardeners using compost tea solutions, beneficial bacteria, fungi and nematodes, mycorrizae, and trichoderma should use purified water.
How do I choose between MH, HPS, and fluorescent lights for indoor growing?
For information on lighting basics, HID lighting, and more - see our Lighting Basics guide.

How do I know what size and wattage of MH, HPS, or fluorescent light that I will need?
For information on grow room size and wattage coverage - see our Lighting Hints guide.

How often should I change my MH, HPS, and fluorescent bulbs?
Bulbs need to be replaced every 8 - 12 months for maximum light output. You will notice a drop in growth rate and fruit size so be sure to stay on schedule. A light meter can help you measure light loss, and you can also go by the bulb replacement sticker and date code on your bulb if you purchased it from us.

What time cycle is optimal to set my light on?
The indoor garden rule of thumb is 18 hours on/6 hours off for vegetative growth and 12 hours on/12 hours off for fruiting/flowering. Be sure to use a timer so it is automated daily at the correct intervals.

Note that the top-of-the-line indoor grow room includes an array of equipment that will help manipulate and maintain an ideal growing environment. Essential equipment includes lighting, grow room ventilation for excessive heat build up, a proper nutrient delivery system or soil garden, sterilization equipment to eliminate pathogens (agents that cause disease such as a bacterium or fungus.) To control excessive heat build-up a ventilation system must be incorporated. This can be done simply with fans, or a carbon filter/fan combination that will clear odor and sterilize the area at the same time. Ideal Grow Room temperatures should be between 65*F and 75*F. If temperatures rise above 85*F your plants will begin to suffer from excessive transpiration, which is the loss of crucial water held within the leaves and stem cell walls. Another factor that ventilation will help control is the relative humidity level or RH of your growing environment. RH can also have an affect on transpiration. Proper humidity levels range from 45%-65% RH. A Thermometer/Hygrometer is a must to maintain proper levels.


Some General Tips:
Lighting systems generally consist of four components: ballast, cord and socket, bulb and reflector. A 400 watt light will cover a 3x3 or 4x4 area, a 600 watt will cover a 4x4 or 5x5 area, and a 1000 watt can usually cover up to an 8x8. Remember the more light you have, the more the plants can feed, thus photosynthesize and produce a fruitful yield.
• When air cooling lights, use at least 250 cfm per 1000 watts.
• Generally it’s a good idea to use 3000 btu of cooling energy per 1000 watts.
• Typically, you will want to exchange the air in your grow room every five minutes. To figure this out use the formula Length x Width x Height = Cubic Ft, then Divide by 5 to get your recommended CFM (Cubic Feet per Minute)
(Example 8ft x 12ft x 8ft = 768 divided by 5 = 153.6 so you would need at least a 153 cfm fan to exhaust your room)

Using Carbon Filters:
Carbon filters are great to use in your grow room. Since you need an air exchange any way, why not sanitize your room in the process? Match the CFM of the filter and fan, attach it to fan intake, and you are ready to go. All carbon filters have a recommended CFM; it is important not to exceed the recommended CFM as the filter will not sterilize the air properly. When mounting your carbon filter it is best to mount the filter high in the grow room to allow any hot air to be filtered first. If mounted and connected properly your fan and filter will accomplish three things:

• Act as an air exchange in your grow room
• Decrease the temperature by taking out hot air
• Sterilize grow room killing mold spores, pathogens, and deodorizing

At what temperature range should I keep my grow room for optimal growth?
Ideal grow room temperatures range between 68° and 75°. Water temperature in hydroponics should be between 68° and 70°.

What size CFM fan should I use for my grow room?
Air exchange should take place every 5 minutes. To figure your grow room exhaust, use the formula Length x Width x Height = Cubic Ft, then Divide by 5 to get your recommended CFM (Cubic Feet per Minute) (Example 8ft x 12ft x 8ft = 768 divided by 5 = 153.6 so you would need at least a 153 cfm fan to exhaust your room).

How should I choose which hydroponic nutrients to use?
First, you should decide if you want to grow organically or conventionally. Second, you'll need to decide what type of growing medium/soil/soiless mix you're using, and if growing hydroponically, what hydroponic system you will be using. For instance, if you are using an aeroponic system, a more liquid nutrient that needs to be used as a thick nutrient like Flora Nova will clog the lines. Most formulas are broken down into 2 stages: a NITROGEN-rich vegetative formula that should be used when a plant is in vegetative stage and a PHOSPHORUS-rich bloom formula that should be used when a plant is in bloom stage. Some formulas are better suited for soil and some formulas like the General Hydro 3 part or Dutch Master are better for high performance hydroponic systems. Please contact our sales staff and we help by making a recommendation based on your needs.

Nutrients in Hydroponics: The role that hydroponic nutrients play in hydroponic gardening is key to ensuring you maintain a healthy, happy plant. Precise nutrient control is one of the major advantages of hydroponics over soil based growing. Some soils have nutrient deficiencies, but after fertilizer salts are added, there is no easy way to change their concentrations. Hydroponics however, makes nutrient manipulation easy.

Specially prepared nutrient formulas can be added directly to the hydroponic solution, providing ideal nutrient balance for various stages of a plant's life. Commercial "grow" and "bloom" nutrient solutions are very easy and rich in proper nutrients. A plant requires more nitrogen at the beginning of its growth cycle, so a nitrogen-rich "grow" formula is used. Grow formulas contain increased levels of potassium nitrate, calcium nitrate and magnesium sulfate, giving the plant a safe nutrient boost for vigorous growth. Once flowers appear, the plant generally requires more phosphorus and potassium. So the "grow" formula is flushed out, and the "bloom" formula is added. By regulating grow and bloom nutrients, more of the plants energy can be put into fruit production at the appropriate time. Click on the chart to the left for common signs of nutrient deficiencies in plants.

Amperage: To figure how much amperage your unit is using, simply use the following formula: Wattage divided by Voltage equals Amperage.

The average household circuit breaker is rated at 15 amps. In other words, if the total amperage drawn from that circuit exceeds 15 amps, the circuit breaker will trip off. You have probably one or perhaps two circuits per room. If you have a 1000 watt unit running off a 120 volt circuit, it will draw approximately 9 amps (1000 watts/110 volts = 9.1 amps).

As for the cost of electricity to run your grow light, we recommend that you check with your local power company, since the cost will vary depending on the geographical area. Find out what you are charged for one kilowatt hour (kW/h) of Power. 1 kwh = 1000 watts for 1 hour. I.E. 10 ea 100 watt light bulbs for 1 hr.

Example - If your charge for 1 kilowatt hour in your area is 6 cents per kW/h, a 1000 watt fixture will use 1.1 kW per hour. Let's say you burn your light 14 hours per day; 14 hours x .066 (.06 x 1.1) = .92 cents per day. If you burn it 30 days per month the cost will be 30 x .92 per day = $27.60 per month. If you burn 400 watt lamps you will use .46 (46%) of 1 kW hour. So it will cost .06 kW x .46 = .028 or 2.8 cents per hour x 14 hours per day = .39 cents per day x 30 days per month = $11.70 month. 1000w fixtures use 1100 watts per hour, 400 watt fixtures use 460 watts per hour, 250 watt fixtures use 295 watts per hour and 175 watt fixtures use 210 watts per hour. The reason the fixture uses more watts than the lamp rating is because of ballast inefficiency and heat loss.

Can I use the same nutrients for soil plant growing and hydroponic plant growing?
All hydroponic nutrients can be used soil crops. Hydroponic nutrient formulas are mineral-based and are instantly available to the plant in any growing medium. But, not all soil nutrients can be used for hydroponics because of the nutrient thickness and release speed of the formula's nutrients. High performance hydroponic systems often have small parts and hoses that can clog easily by thicker formulas like Flora Nova. Often soil nutrients need micro-organisms and time to break down and become available to the plant. By eating the organic material, the organisms present in the soil process the soil nutrient into proper food for the plant. Organic nutrients can be used in a hydroponic system, but we recommend using mediums like coconut fiber or Ready-Gro to provide an environment for beneficial bacteria.

Propagation & Cloning:


  1. Select a branch or stem that has at least 2 or 3 sets of leaves.
  2. Locate a spot on the branch between, or next to, a set of leaf nodes where your cut will be made (leaf nodes are where the branches come out of the stem). Leave at least one set of nodes above the cut.
  3. Make a clean, neat, 45 degree slice with a razor blade or knife. It is important that you do not damage the branch while handling.
  4. Remove the lower 1 or 2 sets of branches (stems and leaves), leaving the upper sets of leaves to be placed above the growing medium line. Trim any flowers or buds that remain.
  5. To prevent an air bubble (embolism) from lodging in the stem where the cut is, immediately dip the base of the cutting into a quality cloning gel, like Clonex or Rootech. Place cutting into your growing medium.
  6. Keep your growing medium moist and warm with bottom heat at all times for best results. Never let your growing medium dry out.
  7. Check your growing medium and transfer cuttings once roots appear or a strong root ball is established.

Additional Tips for Cloning:

  • pH balance your medium between 5.5 and 6.2.
  • Healthy and actively growing plants provide the best choice of clones.
  • Be sure to sterilize your growing medium and any tools needed to do the job, i.e. the scalpel.
  • Keep the bottom heat around 75*-85*F and the ambient greenhouse/indoor temperature at 70*F.
  • Keep your RH high by using a humidity dome. This will help root development by allowing the plant to actively transpire without drying out during the rooting phase.
  • Remove the growth tip and excessive foliage to reduce water loss through transpiration.
  • Fluorescent grow lights are best for seed germination and rooting cuttings. HID lights can be used, but make sure the light is raised high above the humidity dome to keep the seedlings and cuttings from drying out or burning.
  • Don’t over water your cuttings.