Growing in an H-series indoor garden

Growing indoors with hydroponics in an H-series indoor garden.

Growing in an H-series indoor garden

We’ve collected some common questions about growing in a Harvst H-series into this FAQs article.

We’ve also written some other articles about growing indoors with hydroponics:

  • What is hydroponics?
  • Why do roots need to be kept in the dark?
  • Why oxygen is important for plant roots.

Can I use hard water for hydroponics in an H-series?

Using hard water in hydroponics can be challenging and is generally not recommended. Hard water contains high levels of dissolved minerals, primarily calcium and magnesium, which can interfere with the nutrient balance and pH stability of the hydroponic solution.

Here are some reasons why using hard water in hydroponics can be problematic:

Nutrient Imbalance

The excessive calcium and magnesium in hard water can disrupt the desired nutrient ratios in the hydroponic solution. It can make it difficult to maintain the precise nutrient balance necessary for optimal plant growth.

Nutrient Precipitation

When hard water mixes with the nutrient solution, it can lead to the formation of insoluble mineral compounds, causing clogs in irrigation lines, pumps, and the hydroponic system. This can hinder nutrient delivery to the plants.

pH Fluctuations

The mineral content in hard water can lead to pH instability in the nutrient solution. This can make it challenging to maintain the optimal pH level for nutrient uptake by the plants.

Reduced Nutrient Availability

The high mineral content in hard water can limit the availability of other essential micronutrients, potentially leading to nutrient deficiencies in the plants.

We recommend you use soft water or purified water for your H-series. You can use water softeners or reverse osmosis systems to reduce the hardness of the water. Alternatively, you can collect and store rainwater, which is naturally soft and free from minerals.

How long should I run the pump for?

Plants need nutrients, but also the roots need oxygen (see our separate article on this). So, it’s important to not over-saturate the growing medium. The H-series watering trays are designed to fill up to about 10-15mm depth, which leaves an air gap above the water. You’ll see furry “air roots” come out above the water level, which helps the plant get more oxygen in the roots.

The H1, H2 and H3 all fill up at different rates, since there’s a different amount of liquid in flow with more trays. Run the pump for at least 5 minutes on the H1, 7 minutes on the H2 and 10 minutes for the H3.

The frequency depends on what you are growing. Small plants don’t drink much water, and won’t need to be irrigated as often. Perhaps once every 6-8 hours. Larger plants will benefit from more nutrient flow, and if you have full trays of larger plants, consider irrigating as often as once an hour. The pump only runs while the lights are on.

When should I transplant seedlings from the nursery?

Leave plants in the nursery until they have at least grown a set of “true” leaves. The first set of leaves that pop out are the cotyledons, and at this stage the plant is still young, feeding off the nutrients in the seed, and doesn’t need hydroponic nutrients.

Leaving the plants in the nursery gives them a lot of light, keeping them from going leggy, but it’s not automatically watered so you do need to check moisture levels daily.

We usually leave plants in the nursery until it feels like it’s getting a little too crowded, and then move them up to the growing trays.

If your growing trays are empty, you can move the plants up sooner and drop the main grow lights down to give stronger light. If your growing trays are full, then maximise the harvst from your larger plants, leave them growing a bit longer, and leave the seedlings in the nursery.

What is the best plant spacing for hydroponics?

Different plants need different spacing; it depends partly on the root mass for a fully grown plant, and partly on how much light their leaves will need. Here are some rules of thumb.

  • Seeds grown in pots with coir: place the pots right next to each other. This will also keep light away from the nutrient solution and help prevent algae etc.
  • Basil or Coriander in plant cups: 8 – 15cm
  • Leaf lettuce: 12-20cm
  • Chard, spinach beet: 15-20cm

You can move plant cups to space them further apart while the plants are still young, so you can start with a dense crop and then open out, but don’t move plants too often otherwise they will get shocked and won’t grow as well.

It’s very tempting to squash as many plants together as possible, but by giving them space they will be able to make the most of the LED lights, and grow better.

Can I reuse my coir growing media?

Yes, you can reuse coir growing media with proper preparation and care. Coir is a renewable and environmentally friendly growing medium made from coconut husk fibres, and reusing it can be a sustainable and cost-effective option.

Here’s how to go about it:

Harvesting and Storage: After you’ve completed a crop cycle, remove the root remnants and plant debris from the used coir. Rinse it thoroughly with clean water to flush out any excess nutrients or salts. Allow it to dry thoroughly to prevent mould or fungal growth. Store the cleaned, dry coir in a cool, dry place to avoid contamination.

Rehydration: Before reusing the coir, it must be rehydrated to restore its water-holding capacity. Soak the dried coir in a clean water source (with or without added nutrients) until it swells and becomes moist again. Drain off excess water to maintain the desired moisture level.

pH Adjustment: Coir has a neutral pH, so check and adjust the pH of the rehydrated coir as needed based on the specific pH requirements of the plants you intend to grow.

Nutrient Rebalancing: Depending on how many crop cycles the coir has been used for, it may have absorbed and retained nutrients. Ensure that the nutrient content is balanced before using the coir again. You may need to add fresh nutrient solution to replenish any deficiencies.

Replanting: Once prepared, you can plant new seedlings or crops in the rejuvenated coir as you would with fresh growing media.

Keep in mind that coir can degrade over time, and its structure may change with repeated use. It’s a good practice to periodically mix used coir with fresh coir to maintain its physical properties and nutrient-holding capacity. The exact number of times you can reuse coir depends on factors like the initial quality of the coir, the crops you’re growing, and the care and preparation taken during each reuse.

What temperature is best for germination?

The optimal temperature for germination varies slightly among different plant species, including lettuce, salad greens, and herbs, but they generally share similar temperature preferences.

For lettuce, the ideal germination temperature falls between 15 to 20 degrees C. This cool and consistent range ensures that lettuce seeds sprout quickly and uniformly, producing healthy seedlings.

Other salad greens prefer temperatures in the same range. These temperatures promote germination and help prevent excessive heat stress, which can cause bolting (early flowering) and negatively impact the taste and texture of the greens.

Herbs, on the other hand, exhibit some variation in their temperature requirements. Most common culinary herbs, such as basil, parsley, and cilantro, prefer slightly warmer conditions, with germination temperatures ranging from 21 to 24 degrees C.

If in doubt, follow the instructions on the back of the packet of seeds.

How often should I refresh my nutrient tank?

Over time, the tank will build up dirt and debris. Nutrient and pH will go out of balance, too. Your H-series is provided with a nutrient EC meter so you can keep an eye on that, but for pH you will need to monitor manually with a probe, or litmus paper.

There’s also potential for bacteria and diseases to fester in dirty, stale water, so we recommend changing your water and cleaning your tank on a regular basis.

This depends on what you are growing, how old the plants are, and also the quality of water you put in to start with. As a general rule of thumb, once a month at a minimum, and more often if you feel that plants are suffering.

What is the ideal nutrient level for plants indoors?

The nutrient level is measured using Electrical Conductivity (EC). The ideal level for salads, greens, and herbs grown indoors with the hydroponic H-system varies depending on the specific plant and growth stage. We recommend the following:

Seedling / germination stage

Your plants are in the nursery at this point, and can stay in the nursery until they are either too big, or you need the space for the next generation of plants.

The nursery isn’t automatically watered, so if you do leave plants in there for longer than normal, you’ll have to keep a close eye on the moisture level.

Most people suggest that it’s best to germinate / moisten with pure water, since the seeds already contain all the nutrients they need for their first few days of life.

Normal tap water has an EC level around 0.2. If you are putting brand new seedlings in the grow levels, feeding off the main nutrients, try to keep the EC below 1.2 to prevent over-fertilization, which can harm delicate seedlings.

Vegetative Stage

This is when plants are growing the most.

  • EC: 1.2 – 2.0
  • As plants grow and develop more leaves and roots, you can gradually increase the EC to support their nutritional needs.

Flowering or Fruiting Stage (if applicable)

  • EC: 2.0 – 2.5
  • Some herbs may enter a flowering stage if allowed to grow to maturity.