How To Germinate Weed Seeds For Hydroponics

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Starting seeds for hydroponics doesn't have to be difficult. In fact, it's really easy! Learn how to do it in 10 minutes with this Epic Gardening tutorial! Learn the basic steps of seed-starting in hydroponic systems and how to monitor primary variables that affect plant health and productivity in hydro systems. Full picture guide on how to germinate cannabis seeds for hydroponic growing. Foam collars and Rockwool cubes are used to protect the fragile taproot

A Simple Guide to Starting Seeds for Hydroponics

You’re not alone — when I first started gardening, I was a soil gardener.

Starting seeds for hydroponics systems was unknown to me until I started to build deep water culture and ebb and flow systems. Once I built those, I had to learn how to start seeds hydroponically.

One of the main benefits of hydroponics is the absolute control you have over your growing environment. Knowing that, I didn’t want to germinate seeds in soil and then transplant into a my hydroponic system, adding a bunch of dirt to the system.

There had to be another way.

Here are just a few reasons why you want to start seeds in a hydroponic system as opposed to soil:

  • Much cleaner than starting seeds in soil
  • Seedlings grow faster after germination
  • Easy to transplant into a larger hydroponic system

That second reason is a cool one. As soon as your tap root pops out, a hydroponic system is going to help it grow faster than soil and prevent it from becoming rootbound.

Step 1: Get Your Materials

You don’t need much to get started. If you build your cloner yourself, the rest of the materials will cost you under $50 bucks and will last you for quite a while. If you decide to go with a store-bought cloner, it’ll bump up the cost a bit but you’ll also be getting a much higher quality product.

Seed Starting Materials List

    – You can either build your own or use something like the Clone King and starter plugs (#3 below)
  1. Seeds – find at your local nursery if possible, or buy many places online. A personal favorite of mine is RareSeeds.com

Step 2: Fill The Cloner With Water

Fairly simple step here. All you need to do is fill up your reservoir to just under where your net pots sit. Don’t worry about pHing your water or using reverse osmosis right now – standard tap water will be fine.

Step 3: Set Up the Air Pump

Place the air stone in the reservoir and connect the tubing. Connect the other side to the air pump and plug it in. You should see some beautiful bubbles start to come out of the air stone. These bubbles are what will keep the roots of your seeds moist and stimulate growth.

Step 4: Place Starter Plugs and Seeds

Soak each starter plug in some water and then place it in a net pot. The moisture will help the seeds germinate.

Drop 2-3 seeds in each starter plug. We use more than 1 seed because not all seeds will germinate and we want to make sure that every starter plug has a sprouted seed – otherwise we’ll have to replant!

Step 5: Maintenance

This system is very easy to maintain as your seeds sprout.

If you want, you can place a transparent cover over the top to keep in some moisture and increase the temperature of the system, but it’s not necessary.

Make sure to moisten the starter plugs with a few sprays from a spray bottle every day so your seeds have enough moisture to sprout.

When your seeds sprout, clip off all but the strongest seedling from each starter plug.

That’s it! Your seeds should sprout in 3-5 days for most plants and you’ll be ready to start growing some truly epic plants in your hydroponic system in no time!

Video Guide

If you’re more of a visual learner, I have a three part video series from my YouTube channel​ that goes into the entire setup in detail.

Part One: The Basic Setup

This is the visual version of the blog post. Helpful if you just need to SEE to learn (like me).​

Part Two: Making Sure Seeds Germinate

This part of the series talks about some of the maintenance and troubleshooting you might run into when starting seeds, including the infamous “why do they keep falling over” problem that a lot of beginners run into.​

Part Three: pH Water and Add Nutrients

This part of the series talks about the need to pH and add nutrients to your reservoir after the seeds have germinated. Because they feed off of their seed leaves at the start of their life, you can get away with not doing this until the seeds germinate.

By the way, I’m using the Bluelab pH Pen​ to fill all of my pH needs. It’s awesome!

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Hydroponic Seed Starting for Healthy Hydroponic Seedlings

Hydroponics is a technology-based form of controlled environment agriculture (CEA) where yields per square foot can be higher than those of traditional in-soil farming. Crops grown in hydroponic systems require daily management, however, in contrast to some field crops that can be grown with little attention for extended periods of time.

In this article we provide simple steps for successful hydroponic seed-starting, then introduce some of the primary environmental variables that need to be closely monitored to produce healthy hydroponic seedlings:

We do not currently conduct hydroponic trials at Johnny’s research farm, but have compiled this information from our hydroponic trial cooperators, academic and industry resources, and independent hydroponic growers.

10 Steps for Successful Hydroponic Seed-Starting

  1. CHOOSE VARIETIES BRED, SELECTED, AND TRIALED IN HYDROPONIC SYSTEMS.

What to Monitor & Why: The Primary Environmental Variables of Hydroponic Systems

MONITORING TOOLS

You may want to have a few monitoring tools on hand. Most of these devices are reasonably affordable and readily available from hydroponic growing suppliers.

  • Thermometer
  • EC (electroconductivity) meter
  • Light meter
  • pH strips or test kit
TABLE 1. BASIC ENVIRONMENTAL REQUIREMENTS FOR GROWING HYDROPONIC CROPS

TEMPERATURE

Temperatures that are too high or too low will result in poor germination and increase the risk of disease. The optimum temperature range will vary by crop and lifecycle stage; follow individual growing instructions for each crop you are growing.

Once established, plants need an approximately 10°F (12°C) drop between daytime and nighttime temperatures to grow properly. For example, an ideal temperature range for many crops is 75°F (24°C) in the daytime and 60–65°F (16–18°C) at night. Most crops (other than tropical varieties) cannot efficiently photosynthesize at temperatures exceeding 85–90°F (29–32°C).

Supplemental lighting in the protected culture setting can significantly increase the ambient temperature. Also note that to avoid root damage, temperature of the nutrient solution should be maintained no warmer than ambient temperatures.

Plain water normally has a pH of 7.0–8.2. Most nutrient solutions are acidic, and once added to the water source, will decrease the pH.

The pH of the nutrient solution can significantly affect the plant’s ability to take up nutrients. For most crops and hydroponic systems, the ideal pH range is 5.8–6.2 (slightly higher for organic and aquaponic systems).

Ways of measuring pH include using:

  • pH meter
  • litmus paper test strips
  • indicator solution

To understand how pH fluctuates in your specific growing environment, you may want to take routine pH measurements of the following:

  • water source
  • water/nutrient solution
  • growing medium with nutrient solution added

If the pH is off, use a commercially available pH adjustment solution (called “pH Up” or “pH Down”) to adjust your pH accordingly.

If you monitor pH regularly, you will see that the pH slowly rises as the plants take up nutrients. When you replenish the nutrient solution, you will see the pH fall again. More dramatic changes in pH can be indicative of disease; for example, root rot can cause the pH to drop to 3.0–5.0, while algal growth can raise pH levels above optimal levels.

LIGHT

Temperatures that are too high or too low will result in poor germination and increase the risk of disease. The optimum temperature range will vary by crop and lifecycle stage; follow individual growing instructions for each crop you are growing.

DAILY LIGHT INTEGRAL

Growers, particularly in the protected-culture setting, find it useful to quantify light levels in units referred to as the daily light integral (DLI). The DLI is the amount of photosynthetically active radiation (photons) that plants receive each day. Just as you can use a rain gauge to measure rainfall, you can use a light meter to measure DLI, typically expressed as moles of light (mol) per square meter (m 2 ) per day.

RECOMMENDED LIGHT LEVELS

Most vegetables need 14 hours of sunlight per day and at least 12 mol per m 2 per day. Strawberries grown hydroponically prefer 15–25 mols of DLI with a minimum of 12, measured at the canopy level, in the greenhouse. Plants in greenhouses typically experience a 25%–50% reduction in DLI below that of outdoor levels due to glazing and shading from the structure. Depending upon the crop and a host of variables that influence natural light levels, supplemental lighting may thus be needed at certain times of the year or year-round.

LIGHT COLOR

If you are using supplemental lighting, light color is an additional factor to consider. Plants use light within the visible wavelength range of 400–700 nanometers (nm). Herbs and leafy greens fare best with lights emitting a higher proportion at the blue end of the spectrum (450–496 nm), which encourages vegetative growth. Crops like tomatoes prefer lights that emit a higher proportion at the red end of the spectrum (620–750 nm), which encourages flowering and fruiting. Ultraviolet light (UV) aids development of fruit color in crops such as strawberries. LED lights are the most energy-efficient option, and some are adjustable for color to suit crop needs.

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HYDROPONIC NUTRIENT SOLUTIONS & CONCENTRATIONS

The home gardener or beginning grower will want to start with one of the many preformulated solutions on the market. Each comes with its own instructions for mixing and application.

To monitor nutrient concentrations, measure the electroconductivity (EC) of the solution in your system over time. Use an electrical conductivity meter to detect the level of total dissolved nutrients in the hydroponic solution expressed on a scale of milliSiemens per centimeter (mS/cm). The package directions will indicate the desired EC levels. Note, however, that EC is not a reliable indicator if you are using organic fertilizer solutions.

Record the EC when you mix up your solution and then monitor it daily. You will see the EC drop as plants take up the nutrients. Once it falls below an acceptable range, you will want to add more nutrient solution; determine the amount to add based on the percentage drop you have seen in the EC.

You may want to take measurements both from the nutrient solution itself and from sample points in your growing medium; this will allow you to get a sense for whether your growing medium is accumulating a build-up of nutrients.

Temperatures that are too high or too low will result in poor germination and increase the risk of disease. The optimum temperature range will vary by crop and lifecycle stage; follow individual growing instructions for each crop you are growing.

RECOMMENDED NUTRIENT LEVELS

Optimum EC levels vary by crop. Plants will require lower EC in warmer months and higher EC in cooler months and when fruiting. A suggested range is provided in Table 2; however, you will need to experiment to find the optimal range for your crop, season, and growing system.

TABLE 2. NUTRIENT REQUIREMENTS FOR COMMON HYDROPONICS CROPS
REPLACING THE NUTRIENT SOLUTION

A shortcoming of EC is that it does not reveal the specific chemical makeup of nutrients in the water, only the overall nutrient levels. Plants take up individual nutrients at different rates, and thus it is possible for the solution to become imbalanced over time, even if the EC is still within an acceptable range.

For this reason, the nutrient solution should be completely changed on a regular basis. Recommendations on how frequently to change the solution vary; start by replacing your solution every 3–4 weeks, or whenever you see symptoms of deficiency or toxicity in your plants.

ORGANIC FERTILIZERS IN HYDROPONICS

Using organic fertilizers can present more of a challenge than using synthetic ones.

  • The composition of organic fertilizer mixtures is less precise than that of their synthetic counterparts, and nutrient deficiencies can be encountered more readily as a result.
  • Organic fertilizers can also contain high levels of carbon, which in excess can contribute to fungal and bacterial growth.
  • Finally, EC is not a reliable indicator of actual nutrient concentrations, which can also make it harder to monitor and ensure adequate levels with organic fertilizers.

If you elect to use organic fertilizers, we recommend choosing a product specifically designed for hydroponic systems unless you have the capacity to run trials.

WATER

Testing your water source will help you to understand how naturally occurring elements in the water may affect plant growth. If you have hard water (ie, high concentrations of calcium and magnesium in the water), you may want to use a nutrient solution designed for hard water. Water treated with sodium or other water-softening chemicals can be detrimental to plants. High levels of salt in the water can limit calcium uptake and lead to disease (research suggests that water with salt levels of 3000ppm can reduce yields by 10–25%).

CARBON DIOXIDE

Plants need adequate levels of carbon dioxide (CO2) to photosynthesize; low CO2 levels reduce growth and can cause flower and fruit drop, reducing overall yields.

Indoor growing environments can be prone to becoming CO2 deficient. This is most likely to happen in a closed greenhouse system on sunny, cold winter mornings when ventilation fans are not running and plants are actively photosynthesizing, using up available CO2. Plants can deplete available CO2 in as little as just 1 hour in a closed greenhouse.

You can ensure adequate CO2 with appropriate ventilation.

AIR CIRCULATION

Good air circulation helps reduce disease pressure, dissipate pockets of air that are too high or low in temperature, and as discussed above, ensure plants receive adequate CO2. Air movement can also help seedlings develop a thicker stem, producing a shorter, stockier, less leggy plant.

OXYGEN LEVELS

Oxygen is imperative for plant growth. Overwatering and compaction of the growing medium can both limit oxygen to the roots, leading to root death. Using a medium that supports good aeration is important for maintaining healthy oxygen levels.

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Oxygen levels in the nutrient solution are a function of temperature; when the nutrient solution is too warm, the plants’ access to oxygen is compromised. Some growers use an air pump to aerate the nutrient solution and a water chiller to cool the nutrient solution down to an optimal temperature.

Germinate Seeds for DWC (Hydroponic Germination)

This guide will show you how to germinate seeds for DWC (Deep Water Culture) growing.

Starting from clones is much easier than starting from seed when it comes to DWC. Seeds are fragile and require extra care when being propagated for hydroponics. This is probably the one area where soil growers have an edge over DWC. Since soil typically contains trace nutrients simply plopping a seed in moist soil is usually all it takes to get a healthy 3-4″ plant.

Materials Required for DWC Germination:

Paper Towel Germination

Start your DWC germination using a moist paper towel. Wet 2-3 sheets of paper towel using tap water. I don’t bother with adjusting pH this early into the grow. Ring the paper towel out so that it is moist but not dripping.

4.4g dry weight, 35g wet weight for the nerds out there

Spread the seeds out over the paper towel and fold over so that the seeds are sandwiched by at least two layers of paper towel. Work with clean hands and minimize air exposure after soaking.

Put this somewhere warm, 80F is ideal for germination but in my experience, anything above 65F will work fine.

Top of the fridge is an oft-recommended spot but when I actually tested surface temperatures in my house the top of my fridge was about 5 degrees colder than the top shelf in my pantry

If you live in a very cold climate like me and my fellow Canadians you can put the seeds in the oven with the light on to generate a bit of heat. Goes without saying you should put a sign up if you are using the oven method!

After 1-2 days the seedlings should crack and the taproot will begin growing. Leave them a few more days.

After 3-5 days the taproot should be over 1″ long. This is when they are ready for transplant. The seeds were a freebie so I’m ok with the 66% success rate. Typically, you should have 90% or greater germination rate for high-quality genetics.

Rockwool Sleeve

EDIT: Since writing this post I have tried inserting the rooted seedling directly into the foam collar and found it works just as well. IMO the rockwool sleeve is not necessary.

What I do next is something I came up with out of necessity. A full rockwool cube I find to be unnecessarily large. If you’ve read my DIY Cloner article you’ll know that I feel Rockwool can create a low oxygen environment where pathogens thrive.

Rockwool serves a purpose for hydroponics germination. It helps protect fragile taproots and holds water between spraying.

Start by soaking your Rockwool in pH 5.5 water.

Take a Rockwool starter plug and cut it into 4 long strips. Use a clean knife to cut a slit in these strips.

Place the germinated taproot into the slit that you created.

Rockwool Sleeves for Foam Cloning Collars

As per my DIY cloner article I prefer foam collars over neroprene. The foam holds up better and surprisingly absorbs less water.

Trim the foam collar to create room for the Rockwool sleeve

Aeroponics Cloning Nutrient Solution

  • 1 Gallon Water (Target pH 5.5) (1 mL each Micro, Gro & Bloom)
  • 1.2 mL of Rapid Start

A few drops of pH Down gets me down to 5.5

Unlike soil (which has trace nutrients) cloning/germination in hydroponics requires immediate additions of nutrients. Once you get the pH to 5.5 add:

  • 1.2 mL GH Rapid Start
  • 1 mL of FloraGro
  • 1 mL of FloraMicro
  • 1 mL of FloraBloom

My starting ppm was 100 and the final ppm was around 300.

Seedling Growth

From here the process is the same as with clones. Simply run the pump on a cycle timer and let nature do its work.

The plants will not look happy on day one, but don’t worry they will perk up quickly under the light.

Rockwool Watering (Why I started using aeroponics for germination)

aeroponics cloner I needed to water the seedlings multiple times per day, even with the humidity dome! You can also see why I have the plants so close to my light now. Fluorescents are not very strong and can cause extreme stretching if they are not within a few inches of the plants.

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