Spend a good amount of time in any hydro shop across the country and you’ll hear a myriad of different questions related to growing plants hydroponically. But you’ll start to see some patterns forming, too. Here are 10 questions Matt LeBannister has heard over the years working in an indoor gardening store.

How often should I empty and replace my reservoir and nutrient solution?

Reservoirs should be emptied and the nutrient solution replaced at least every 5-7 days. People often use their EC/TDS meters to measure nutrient levels and top up their nutrient solution when levels get low. EC/TDS meters only measure overall salt levels, not the levels of specific nutrients. This means nutrients not completely used by your plants will begin to build up to potentially toxic levels. Emptying your reservoir and replacing your nutrient solution with a quality fertilizer is the only way to ensure nutrient levels are consistently in the ideal range for plant growth.

What is the difference between organic and inorganic fertilizers?

Organic fertilizers are derived from natural, organic compounds such as compost, manure and worm castings. Inorganic fertilizers are created using inorganic compounds made through chemical processes. As far as your plants are concerned, organic and inorganic nutrients are relatively the same.

They can have virtually the same nutrient levels, and at a molecular level these nutrients are the same. Many organic fertilizers need symbiotic fungi and bacteria to break them down before the fertilizer is readily available, while others are pre-digested and instantly available to your plants. Some people find that organic nutrients allow more sludge to build up in their reservoir. Just remember, it is not safe to use hydrogen peroxide with organic nutrients, as it will kill off all the beneficial fungi and bacteria.

Which nutrient supplements can I use to increase flower size?

There are many supplements that will increase flower size. Most common are bloom boosters that are concentrated in powder form and are high in phosphorus. Bat guano supplements also increase flower growth and I also really like foliar spraying with folic acid, often labeled gold. This will increase the number of flower sites and act as a chelating agent, helping your plants absorb macronutrients more efficiently.

What is the ideal growroom temperature?

The ideal growroom temperature varies depending on what types of plants you are growing. Tropical plants like orchids and plants like succulents do well at 80°F and up. Plants such as kale and broccoli do best at cooler temperatures in the

60- 65°F range. Plants like tomatoes do well in the 68-75°F range. Temperature is important for more reasons than plant growth. When the temperature surpasses 80°F, insects can multiply much faster than at cooler temperatures. Soil and soilless mediums will dry out more quickly, increasing water consumption, and soil will become toxic with concentrated nutrients. The higher temperatures also reduce the amount of oxygen available in the nutrient solution.

What is that scum in my reservoir? And how do I prevent and get rid of it?

That scummy, sludgy buildup in your reservoir could be algae, bacteria or fungi. These organisms rob your reservoir of oxygen and nutrients, leaving nothing for your plants. They clog pumps and drippers, causing nightmares in the growroom. Regardless of what it is, it is usually caused by light entering your reservoir combined with higher reservoir temperatures.

Keeping your reservoir cooler, either with a reservoir chiller or by keeping your room cool, will make a huge difference. Covering your reservoir with either a lid or black and white plastic, white side facing up, will keep the light out.

You can also add hydrogen peroxide to your nutrient solution at each reservoir change to help eliminate the sludge. Cleaning your reservoir between crops is important to keep the sludge from returning. You can use a diluted bleach solution of one part bleach to five parts water, or there are many food-grade industrial cleaners available that will do the trick.

How often should I replace my HID light bulbs?

HID light bulbs come in a variety of spectrums and strengths to meet the needs of indoor gardeners. The lumens and PAR (photosynthetically active radiation) levels drop quickly. You can check this for yourself by measuring your yields with new bulbs versus bulbs that are 8-12 months old.

The newer bulbs in the same environment should offer noticeably larger yields over the old ones. After 8-12 months of continuous use, the bulb should be replaced.

What are the benefits of growing with hydroponics?

There are numerous benefits to gardening using hydroponics. Hydroponic systems use less water than traditional gardens. They are also cleaner, since you are not bringing soil into your home. Hydroponic systems are less likely to host destructive insects, and you can grow indoors year-round.

The biggest advantage hydroponics has over traditional gardening is significantly larger yields in less time. That means more crop rotations per year, and more money in the pockets of commercial growers. This is because hydroponic plants are able to use twice the nutrients that plants in traditional gardens can.

What is powdery mildew and how do I prevent and treat it?

Powdery mildew is a fungal infection on plant leaves caused by high humidity and poor ventilation. Preventing powdery mildew is as simple as keeping your growroom’s humidity level below 65% and providing ample air circulation. Air circulation can be improved by venting your room more often. Including ceiling fans or oscillating fans in your room can make a big difference.

Spraying your leaves with the lights out can invite powdery mildew onto your plants. There are a couple ways to treat powdery mildew. Spraying or dusting your plants with sulphur will kill the powdery mildew.

Neem oil and pine tree oil foliar sprays also work at removing and preventing powdery mildew. For large-scale removal, the best choice is a sulphur burner. This will vaporize sulphur pellets, filling your room with a sulphur mist, killing the powdery mildew.

Why are my leaves turning yellow and what can I do about it?

There are numerous reasons why your leaves may be yellowing. The most common problem is a yellowing of the older, lower leaves on the plant. This is caused by a nitrogen deficiency. There is not enough nitrogen available for your fast-growing plants, causing them to take nitrogen from the older leaves and send it to the new shoots. This can usually be corrected by adding some more nitrogen to your feeding schedule.

Adding worm castings and pine tree oil are two safe ways to get more nitrogen to your plants. If the yellowing is occurring in the newer leaves, it is likely caused by a micronutrient lockout. The usual cause of this is a toxicity of either phosphorus or potassium, or high or low pH levels.

Flush your growing medium with pH-balanced water and begin watering with a quality nutrient solution. Heat from your lamps can also cause some of the leaves closest to the bulb to turn yellow or even dark brown.

Simply position your bulbs further from the canopy. Finally, overwatering can turn leaves yellow. The lack of oxygen available in the root zone will starve the plant and affect chlorophyll production.

How do I know if I have spider mites? And how do I purge them from my plants?

This is the most common customer question I get asked. Spider mites are the bane of every indoor gardener’s existence. These miniscule insects feed on your plant’s juices and can decimate crops. Spider mites are hard to detect, mainly because they are so small, and once you realize you have them, it is often too late.

You may notice stunted growth initially, then on closer inspection, there may be some webbing in your plants. The damage will show up as dried-out silvery spots on the younger, more vulnerable leaves, which will die and drop. Affected plants can be treated in a variety of ways.

Many people resort to insecticides. You can also spray plants with neem oil or homemade insecticidal soap (water, dish soap, garlic and cayenne pepper). These two remedies will coat the body of the spider mite, preventing molting and reproduction. Make sure you spray the undersides of the leaves, as this is where many adults and eggs are hiding. Another solution is predatory insects.

Predator mites and ladybugs make great natural spider mite controls, but do not use beneficial insects along with any pesticides or sprays because they will kill the good bugs as well as the bad ones. The best way to deal with spider mites is to prevent them from getting into your indoor garden in the first place. Always be clean and wash up before entering your growroom.

Avoid touching your plants to prevent bug transfer, and keep pets away from your plants. Keeping your growroom temperature below 75°F will also help keep spider mite populations down, as the higher the room temperature, the faster the spider mites can reproduce.