A bit over a week ago I planted some spinach seeds, and sadly they didn’t germinate. I began a bit of research as to why. Despite my spinach varieties being hardy to warm weather, they still need cooler soil to germinate! The adult growth stage can handle warmer temperatures but the seedlings are too vulnerable still.
I began to wonder what I could grow with my current temperatures. It’ll also be handy to know the minimum temperatures for when the seasons change.
Whilst my plants aren’t being planted in soil, instead hydroponic is usually planted in rock wool or peat moss, the germination temperature should theoretically remain the same.
Amaranth, Red Leaf
Basil, Purple Petra
70 – 90
21 – 32
Kale, Nero Toscana
Lettuce, Little Gem (Romaine)
5 – 24
Lettuce, New Red Fire
Lettuce, Red Sails
Lettuce, Red Salad Bowl
Swiss Chard, Bright Lights
Swiss Chard, Lyon
50 – 75
10 – 24
Taisai, Pak Choy
10 – 27
Tomato, Marmande VR
60 – 70
15 – 20
Tomato (Cherry), Supersweet 100 FT
Tomato, Sam Marzano
I measured my Aerogarden water and it’s hitting a maximum of 85°F (30°C)! No wonder my spinach never sprouted, its ideal temperature is 50-75°F (10-24°C). Its just way too hot for them.
I’ll have to wait a while for the weather to get a bit cooler before I can sprout spinach; in the meantime I can try growing some Bright Lights Swiss Chard and Nero Toscana Kale.
Plants often have a recommended spacing when growing in soil, and I was curious if they had to same requirements when growing hydroponically. I’d like to grow several plants at once, maximising the shelf space that I have.
It would be great to have several lettuce growing in one container. I plan to harvest the larger leaves as they become available, leaving the plant to continue growing, rather than harvest the entire plant in one session.
Why Plants Need To Be Spaced
If lettuce are grown too close to each other
they will likely receive less than the required amount of light… they can also receive less air/CO2 than they require for proper growth.
It seems that adequate airflow is also required to help reduce mildew and other diseases. And plants need to meet a certain level of light in order to grow; I learnt this the hard way in the post Do I Need Grow Lights?
What Spacing Is Ideal
There doesn’t seem to be a consensus of how close net cups can be before lettuce growth becomes detrimental; measured centre to centre of each cup. Part of the problem lies in what plant is being grown, as well as when and how often it is harvested. For example a larger plant (like a tomato) will definitely need more space to grow than a smaller plant (like a lettuce). Secondly, many assume you would harvest an entire mature plant in one session (such as commercial growers), whereas some people prefer continual harvesting where they only take a few outer leaves at a time and let the plant continue growing.
WeGrowHydro claim that plants should be spaced a minimum of 18″ apart (45cm) for plants less than 3 feet in height! For me that’s a total of 1 plant per shelf! If they had to point out plants less than 3ft, it makes me wonder if the plants they are growing are much larger than lettuce…
Bernard Kratky himself, the founder of the Kratky hydroponic method, wrote in a paper:
“Two common planting densities for lettuce are 1.5 and 1.9 plants per square foot”.
That calculates to one lettuce every 6-8″ (12-20cm) for commercial growth. Again, this assumes that the entire plant is harvested in one session.
Steemit claims that lettuce should be at least 6 to 8″ (12-20cm) apart. However their article looks like it’s written for commercial growers – or large setups where you might harvest entire lettuce in one session.
Christian Haschek‘s blog shows a vertical hydroponic setup where he spaces the cups by 4″ (10cm). This is the first case I have found where the hydroponic setup is aimed towards home-growers rather than commercial, so it could be assumed that he harvested individual leaves or perhaps before the plants became fully mature.
Even my Aerogarden Bounty has spacing of only 4″ (10cm) between each pot. This system is definitely aimed at the home grower, encouraging continual harvesting of the plants.
What Spacing Do You Use?
I’m curious to know what spacing you used? Please share with us what plants you have grown and what spacing you used between net pots (centre to centre).
Plants can’t survive from water alone; they need nutrients as well. In traditional growing, the plants will often get what they need from the soil (and even then you often still add fertilisers). But hydroponics removes the soil. Instead you need to use hydroponic solutions with the correct ratios of nutrients; too much or too little and your plants will suffer and potentially die!
I use General Hydroponics Combo Ferilizer pack for my hydroponics. In fact a lot of people recommend this brand. This brand has split the different nutrients a plant needs into different bottles. Plants need different amounts of various nutrients depending upon their growth stages; and the General Hydroponics Combo pack comes in three bottles that each contain different concentrations, allowing you to target each growth stage and get maximum growth and yields!
Mix the following amounts of nutrients into one gallon, or 3790ml, of water. I recommend filtered water to help reduce debris and other microbes from entering your hydroponic systems.
All nutrient measurements are taken in teaspoons.
Seeds & Cuttings
Late Vegetative to Pre-Bloom
Bloom to Fruiting
I use the vegetative ratios of 3-2-1 for my Kratky lettuce since its main goal is to grow vegetation and leaves. Ideally I don’t want my lettuce to bolt and flower as the leaves will turn bitter.
Want to try out hydroponics, but don’t want to spend much? Honestly it’s a big field with lots of complex terms and companies selling you the “next must have” item…. Let me help you create your first hydroponic setup without spending much, or maybe even without spending a single dollar!
Our goal is to create a “set and forget” system to grow lettuce.
Most people will do their first hydroponics with mason jars. They are such a versatile jar that pretty much every house has one, and they are cheap!
I personally recommend the largest jar possible; it’s more “set and forget”. Lettuce roots don’t need too much space to grow, but depending upon your environment and its growth rate you may find yourself adding water to a small jar every so often.
Hydroponic containers have to be opaque and black to stop algae growth… but you won’t find any mason jar like that. Instead, wrap the jar well with aluminium foil, or even paint a couple layers of black gesso or acrylic paint on the outside! If use chalk paint and you can later write or decorate your jars with chalk pens.
The Yoghurt Cup or Net Cup
If you have plenty of plants around your home, you may have a net cup already. They are often those little plastic cups with slots or holes in them that come with smaller plants. Make sure it fits. I use these 2″ wide-rim cups from CZ Garden.
Alternatively, you can recycle a plastic yoghurt cup. To be safe, please check What Plastic Should I use for Hydroponics? as not all plastics are safe to reuse. In the picture below you can see how I reused a sour cream cup:
Plants will often get all their nutrients from the soil you plant them in, although sometimes you will add fertilizers or compost. Hydroponics removes the soil from the growing process, so you need to come up with an alternative way to feed the plants nutrients.
Next you need to decide what plant you are going to grow: lettuce and basil are some of the most common plants for people to try for their first grow since they are fast growing, cheap and easy to manage. With the right setup you can even grow big plants like tomatoes (but they won’t grow in mason jars, sorry)!
GettyStewart has a great post about How to Regrow Romaine Lettuce from the Stem. She does point out that regrowing from a stem won’t produce leaves as large as store bought plants; and this probably has to do with the amounts of nutrients and lights that a store-bought plant receives compared to a stem in plain water.
I prefer to grow from seed; it has a fairly high success rate and only takes two to three weeks before I am harvesting. You can buy packs of various seeds fairly cheap, or individual packs from stores such as Botanical Interests.
Hydroponics is mostly about removing the soil from growing plants, but you can’t just plop them into the water and hope for them to survive (some plants do, but most wont)!
You will need some form of grow medium. There are several different options with the easiest and most common being peat moss, rock wool and clay pebbles.
I regularly use Jiffy 7 Peat Pellets. They come in various sizes. Since the peat pellet is too small to fill up my entire DIY net cup, I pack clay pebbles around it. Alternatively you can use rock wool. You can simply cut up extra rock wool cubes to fill any spaces in your net cup. If you don’t want to cut up the extra rock wool, you can of course use clay pebbles as well.
It’s important to fill up the entire cup; we want to make sure that no light will get beyond the grow medium and into the mason jar.
Most people will put their mason jar and plant in the window, and generally there will be sufficient light for plant growth. Unfortunately my kitchen window is underneath a building overhang and thus gets very little light; so I need a grow light.
If you opted to paint your mason jars black, now is the time. Paint only the outside of the jar, remember that the paint itself is unlikely to be food-safe. Paint right up to the rim of the jar. Paint two to the three layers so that no light can leak inside.
Cut Your DIY Grow Cup
If you are using a recycled yoghurt cup, its time to cut some slits and holes in the bottom of the cup. Slits are generally better as they hold the grow medium without spilling, but still provide enough space for roots to grow through.
Any non-living supply should be sterilised; jars, containers, and grow medium. The easiest way to do this is to submerge everything in hot water.
Fill your mason jar until the water level passes the bottom of the grow cup or yoghurt container by approximately .25″ or 1cm.
If you have excess water left over, you can water other plants with the mixture or store it to top up your lettuce water. You should not pour it down a drain! I store my excess nutrient mixes as I live in a dry climate and find water tends to evaporate faster than the plants are able to absorb.
Plant Your Seed
Make a small hole, usually about .25″ or 1cm deep, in your grow medium. Drop two to three seeds in and fluff grow material on top to cover lightly. Not all seeds with germinate, so it’s generally a good idea to put at least two seeds. If multiple sprout, you can always transplant or pull out the extra growth.
Place your grow medium in the centre of the cup, ensuring that the bottom of the grow medium is in contact with the water. Surround your grow medium with clay pebbles, or more rock wool.
Set and Forget
Place your mason jar somewhere bright, like a window.
And thats it! Over the next few days your plant should sprout. Some plants do take longer to sprout, so check your seed packet. My basil usually sprouts in about 5 days; at least you can see the tiniest of plants emerging around then.
If your plant didn’t sprout:
You may need to wait longer; check on the seed packet for how long it takes for that variety of plant to sprout. Some species can take 20 or more days!
Make sure your grow medium is moist the entire time the seeds are sprouting; if you live in a very dry environment your water level may evaporate too fast for the seedlings to produce roots.
You could also have some bad seeds, try refilling your jar and planting more or new seeds.
If you notice your plants becoming wilted, chances are the water level is evaporating faster than they can absorb. Fill up your jar a little at the time! It’s very important to not fill the jar up the entire way; as the water level decreases the plant will grow water-roots and air-roots. If you submerge your air-roots in water your plant will literally drown. If you want to maintain your water level, I suggest the half-way point of the jar.
If your plant seems to be growing long leaves that aren’t very wide, you may not have enough light. Check out my post Do I Need Grow Lights? where I teach you how to measure the amount of light in your room.
On the 1st August 2019 I planted several spinach seeds in Jiffy 36mm Peat Pellets. Just after planting I discovered my new grow light arrived faulty, so my plans changed; rather than waste the seeds and peat pellets I started my Aerogarden Bounty; in that batch were three Lavewa Spinach and three Matador Spinach pods.
I also happened to start some San Moranzo Tomatoes. The tomatoes both sprouted three days ago, but so far not a single spinach sprout has emerged!
According to Botanical Interests (the seed supplier) both spinach varieties can take 5-10 day to emerge. So there is still hope. Fingers crossed.
Once replacement grow light arrives I will transplant any seedlings to the Kratky buckets, their final home.
At first they were really unhappy, and I expected them to die. Not only was there the stress of transplanting, but I moved them from Jiffy 36mm Peat Pellets to cloning collars! Double damage to the life bar (video gamer speak).
Don’t they just look sad?? Well, thankfully they have perked up so much since then!
For some reason one of the lettuces recovered faster than the others, and this gave him a significant growth spurt. The front lettuce are all slightly larger than the ones at the back and I am unsure why; they should be getting about the same amount of light, temperature and nutrients.
I’ve seen some Youtube videos and articles where they grow their hydroponic plants in pool noodles. They claim to get high harvest yields, and they regularly talk about the benefit of being able to reuse the pool noodles.
I was concerned about the safety of using pool noodles; as we know plastic can leach chemicals and micro-particles into the water and plants (and eventually you). This process is often sped up with exposure to high temperatures… and Kuwait set a world record for the highest temperature in the world reaching 52.2°c (126°f) in the shadows and 63°c (126°f) in the direct sun!
After I bought the collars I realised that there weren’t many people online saying you could start seeds in the collars; they are generally used for transplanting cuttings from older plants.
I decided to do an experiment on whether I could grow seedlings in cloning collars.
I’m starting this experiment on Aug 7, 2019.
I sterilised the cloning collar and the container with hot water.
If you look closely you can see the Lemon Cucumber seed in the middle of the cloning collar. I’ve inserted it so its very close to the bottom of the collar (I’m holding it upside down), but far enough in that it hopefully doesn’t fall out.
Apparently seedlings will grow best when exposed to high levels of humidity. I wanted to make sure that my seedling could get as much light as possible at the same time. So I found this old Ikea air-tight plastic container. It has a de-gas spout which I have kept closed.
Fingers crossed that this container won’t grow algae since my nutrient rich water is also exposed to light.
I needed to make space in my Aerogarden Bounty to plant some new seedlings, so rather than kill the entire crop I decided to try and save them by transplanting to my Kratky container.
Transplanting from the Aerogarden Bounty can be quite difficult; the fine roots of the hydroponic lettuce wrap around the plastic support bars, and unfortunately rip easily when removing from the cups.
I was also using the Jiffy 36mm Peat Pellets which have a very fine mesh wrapping, and removing this mesh would rip any remaining small roots. Normally you wouldn’t have to remove the mesh, or even seperate the lettuce from the peat pellets, however I wanted to try out my new cloning collars.
By the time that the lettuce was removed from the Aerogarden Bounty container and the Jiffy had been removed and all peat washed off, only the major roots of the lettuce were left. The poor plants were definitely going to go into shock, and may not survive at all.
Ouch. It doesn’t look like the lettuce is going to survive; I think I pulled off too many roots and shocked the plants way too much.
Since the roots are so short now I have the water level half way up the net cups. This leaves very little space for any air roots to grow, especially given the size of the lettuce already.
They still look bad, but thankfully at close inspection they seem to be recovering slowly. It’s hard to tell in the photo, but they are a little perkier than on Day One. You can see the centre back lettuce sticking one of his leaves straight up now, compared to yesterday’s droop.
The lettuce at the front right seems to be the last to start recovering; none of his leaves are currently stiffening up again.
I pulled off some of the biggest leaves that did not look to be recovering (and ate them); I want the plant focusing on fresh growth of roots and new healthy leaves rather than saving pre-existing leaves.
The lettuce are definitely recovering by this point; the centres are much more perky and green.
Generally you shouldn’t expose the Kratky nutrient solution and roots to light, but I couldn’t resist a quick look to see how the roots were recovering.
The roots are all slightly brownish, with several potential reasons: firstly the nutrient solution is a brownish tinge and could be discolouring the roots, or secondly there could be root rot developing. If the roots turn dark brown or black and become slimy then I have root rot.
The lettuce that seems to be recovering the most are on the left side of the container, which is reflected in their root development; these two lettuce have already grown roots beyond their net cups! Surprising how fast they grow!
You can’t see it in the photo, and its hard to see in person even, but some of the roots have started to develop a white fuzz. Here is an example of a reddit user with the white fuzz on their roots. This is not mold and is actually a sign the plant is “healthy” (or in this case recovering) as it helps with nutrient absorption. The roots are expanding their surface area and will either develop longer roots from these points, or remain fuzzy.
I’ll keep an eye on the lettuce and post an update in a few days. Fingers crossed they will fully recover. Until then, have you had any transplant success or failures?
I’ve heard a lot of people online say that they have had decent success with growing tomatoes in hydroponics, so I wanted to test just how easy it was myself.
This is the growth after 1 week, planted on 1st August 2019:
I planted some seeds into Jiffy 36mm Peat Pellets. Unfortunately just after planting we discovered that our grow light was faulty! Rather than waste the seed and peat pellet, I decided I would just start a new session in my Aerogarden Bounty. Once my replacement grow light arrives I will remove from the peat moss and transplant into a cloning collar.
They began to emerge from the pellet only three days ago, with the smallest white to very pale green sprout showing. They are growing so fast as they reach for the light!
Strange enough the second seedling grew two sprouts. I am pretty sure I only placed one seed in each pellet.
It looks like the two sprouts merge into one stem close the soil. I don’t want to disturb the peat moss yet. If there is more than one seedling in the pot I can seperate them when I transplant; hopefully my new light will arrive soon.
Have you grown hydroponic tomatoes? I would love to know how well they grew for you.
Hydroponic plants are always grown in some form of container; in essence they are a container with water, and sometimes fancy tools like pumps. A lot of people grow small produce like lettuce in mason jars using the Kratky method, but most commonly plants are grown in plastic buckets, totes or buckets.
Keep It Food Safe
It needs to be food-safe, and yes this is important. Many people will use plastic containers but they are often unaware that overtime plastic degrades and can leach micro-particles and chemicals into the water, all of which will be absorbed by your plants as they grow (and subsequently eaten by you).
Plastic leaching these dangerous chemicals are even worse if you live in a hot environment, and if the plastic is exposed to heat at any time (such as at the store before you bought it). Furthermore, some plastics will react if exposed to certain products, especially if they are too alkaline or too acidic.
The wrong chemicals exposure can be dangerous. BPA and some phthalates are endocrine disruptors, mimicking natural hormones and causing a cascading number of different health problems such as infertility, obesity, breast cancer, prostate cancer, reproductive development, heart disease, diabetes… and more.
Polypropylene (PP) is another common used plastic; found in many food storage containers and microwave safe containers. This plastic can be heated safely, and it doesn’t react to liquids, acidity, or alkaline foods.
High-Density Polyethylene (HDPE) is often found as dairy containers (milk or butter), cereal box liners, and large food buckets. It doesn’t absorb liquid, and futhermore doesn’t leach chemicals into their contents.
What Plastics Should I Avoid
Recycled Plastics Any plastic that is recycled may not be food safe. I would avoid any recycled plastics for hydroponics.
A quote from the FDA describing the risks of recycled plastics:
1) that contaminants from the post consumer material may appear in the final food-contact product made from the recycled material, 2) that recycled post-consumer material not regulated for food-contact use may be incorporated into food-contact packaging, and 3) that adjuvants in the recycled plastic may not comply with the regulations for food-contact use.
PVC. Did I just say that right? Yep. A lot of DIY hydroponics use PVC pipes to store and run their hydroponic solutions, and even grow their plants. In it’s rigid form PVC is probably safe, however in its flexible it could be dangerous. To make it soft a plasticiser is added, often up to 40%! According to Choice Australia recent studies have raised concerns about the health risks.
Polycarbonate should be used with caution. Whilst a lot of food storage containers are made with this plastic, recent studies have suggested that polycarbonate can release bisphenol A (BPA) which can cause serious health problems.