Growing San Marzano Tomatoes in Kratky Hydroponics – Update: Week 1

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!

Tomato Seedling Week 1
Tomato Seedling Week 1

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.

Tomato Seedling Week 1
Tomato Seedling Week 1 – Look at his little seed hat!

Have you grown hydroponic tomatoes? I would love to know how well they grew for you.

Expected Grow Times of Kratky Hydroponic Plants

I’d like to figure out how fast I can expect my plants to grow. Most seed packets and websites tell you how fast seeds grow assuming you are using soil, But hydroponics can grow up to 50% faster!

I doubt very much that my first hydroponic plants will grow 50% faster, however that doesn’t mean that I couldn’t expect to start harvesting from roughly that time onwards. You rarely need to wait until the plant reaches full maturity before you can harvest; just pull off leaves as needed and let the plant keep growing. I added “Potential Maturity” to the table below, but realistically that’s when I suspect I may be able to get my first harvest.

Earlier in the week I announced that we were hoping to grow the following vegetables and fruits in our Kratky hydroponic tubs:

  • Amaranth, Red Leaf
  • Basil, Purple Petra
  • Cucumber, Lemon Cucumber
  • Lettuce, New Red Fire
  • Lettuce, Red Sails
  • Spinach, Matador
  • Spinach, Lavewa
  • Swiss Chard, Bright Lights
  • Tomato, San Marzano

All of our seeds were purchased from Sustainable Organic Q8, and appear to have been imported from Botanical Interests. You can read more about my search from seeds in the post Where to buy organic seeds in Kuwait.

Days To MaturityPotential Maturity
Amaranth, Red Leaf90-11045-60
Basil, Purple Petra45-5523-28
Cucumber, Lemon6532
Lettuce, New Red Fire5527
Lettuce, Red Sails4523
Spinach, Matador28-4814-24
Spinach, Lavewa28-4514-24
Swiss Chard, Bright Lights5226
Tomato, San Marzano80-9040-45

I’d really to have some plants growing, or even harvestable, by late September/early October. Thats approximately 50-60 days from now. We have space for 2 large plants, along with at least 3 smaller plants and maximum of 5 plants.

San Marzano Tomato Artwork, Courtesy of Botanical Interests
San Marzano Tomato Artwork, Courtesy of Botanical Interests

The San Marzano Tomatoes are planned as a permanent setup, so these will take priority in one of the largest plant spaces. This tomato plant will be approximately 5-6 feet (1.5-1.8m) in height!

Lemon Cucumber Artwork, Courtesy of Botanical Interests
Lemon Cucumber Artwork, Courtesy of Botanical Interests

Whilst not quite as large as the tomatoes, the Lemon Cucumbers will stand about 3-4 feet (0.9-1.2m) in height. This will fill my second large grow area.

There are debates online about which spinach is “better”; matador apparently grows better in many conditions, but the Lavewa looks prettier and is slightly tastier. We want to test both of these spinaches side by side. They grow at the same rate, so we will test both the Lavewa Spinach and the Matador Spinach together.

Amaranth Artwork, Courtesy of Botanical Interests
Amaranth Artwork, Courtesy of Botanical Interests

I want to stagger the harvesting of my plants; I don’t want all my fresh leaf plants to mature at the same time, and then go one to two months with little food. So I have decided that I will start the Amaranth as well for this first hydroponic growth cycle. Granted, with its growth speed, I may be able to grow two batches of spinach by the time it reaches full maturity.

If I can fit anymore plants in my grow area I will add the Swiss Chard and the New Red Fire Lettuce.

What about you?

What are you growing this season? Did you calculate how long it takes to grow? Did you have to plan around seasons and temperature outdoors? Let me know what you’re growing!

Where to buy organic seeds in Kuwait

After researching a bit, and probably jumping into the water too fast when it comes to buying products like grow lights, I have purchased some seeds to grow in my Krakty hydroponic room setup.

Buying seeds was a specific hassle in Kuwait; the very few and limited stores that sold seeds only sold very common varieties. Think Beefsteak tomatoes; the probably most common tomato you can find at any supermarket. Since such tomatoes are so easy to buy, I want to grow something more unique.

In fact, we even found a nursery selling seeds with the giant warning label on the back: “Warning. Treated with poison. Do not consume or grow food products from these.” What?!

In the end we found a company called Sustainable Organic Q8 that seems to import from reliable producers.

The initial seeds that we have ordered are:

  • Amaranth, Red Leaf
  • Basil, Purple Petra
  • Cucumber, Lemon Cucumber
  • Lettuce, New Red Fire
  • Lettuce, Red Sails
  • Spinach, Matador
  • Spinach, Lavewa
  • Swiss Chard, Bright Lights
  • Tomato, San Marzano

Hopefully within the week we will have the buckets and grow lights and started growing!

How Bright Should My Hydroponic Lights Be?

In the post Do I Need Grow Lights I measured the amount of light in each of my grow rooms, hoping to figure out which room would produce the best plant growth. At the time I was hoping to not have to invest in a grow light; man was I wrong!

A Short Warning

LUX, or lumens, to determine plant growth is widely inaccurate due to the different types of lights and the wavelengths light types each produce. Plants need certain wavelengths, or colors, to grow. No matter how bright your lights are if they are missing those wavelengths then then the plants will just not grow.

This post will not consider the wavelength or colors of lights. I’m trying to keep it as simple as possible so that anyone can follow along, even without fancy gadgets like quantum meters which can easily cost US$500. Future posts will explain wavelengths in detail. Beginners Guide To Hydroponic Lighting has a list of all the posts on how to measure and set up your lights.

You need the umol’s value or the umol/s/m2: in essence umols are how bright your light is. This value is also known as “photosynthetic photon flux” or PPF. Note that PPFD is a different value, taking into account the distance from the light.

Too low of a light strength on your plants may lead them to not growing, and too high may burn or kill them.

How To Calculate Bright Your Light Is

Most people don’t have fancy tools to measure the amount of light in their homes, such as a PAR meter or a quantum meter. Thankfully, you can get free apps on your phone that measure lumens easily.

You can use the Plantekno website to convert LUX to umol/s/m2. Note: many grow lights will tell you the PPF or umol/s/m2.

Natural sunlight has a PAR value of 900-2000μMol/m2/s when directly overhead, varying with location and season. For a grow light to be effective, it will have PAR values of 500-1500 μMol/m2/s.

In comparison, I measured my kitchen window light at 250LUX or 4.6umol/s/m2. No wonder my plants kept dying! As you’ll see below, its way below the minimum light requirements for lettuce to grow.

But how bright should my light be?

Be aware that not all aspects of how much light plants need are fully researched yet : Lefsrud at McGill University has extended upon NASA research and one thing he noted was common incorrect assumptions. For example, many people consider lettuce to a shade loving plant and tomatoes to enjoy full sun. However when shone with 5000 umol’s, the tomatoes suffered whilst the lettuce showed no signs at all! The exact opposite of what was expected.

Research Gate website had several listed studies that mentioned the number of umol’s used for ideal plant growth:

Minimum umol’s Required
Lettuce100-200
Watermelon250
Tomatoes400-500

According to the company Valoya the amount of umol’s a plant needs will vary depending upon its growth stage: seedling, vegetative, flowering/fruiting. They claim that lettuce needs approximately 80 umols during seedling, 150 for vegetative stage and 200 when it begins to flower.

Valoya’s Comparison of umol’s for Lettuce Growth

I found a really great article from the Department of Horticulture and Crop Science: this PDF covers a huge variety of plants, and the recommended lighting and hours lit for each of the growth stages, and what level nutrient solution is ideal.

Here is a small sampling of some common plants and their needed light intensity (taken from above PDF link):

Lettuce

# Light HoursLight Intensity
(umols)
Propagation12-20150-250
Vegative12-20250-450
Flowering12-20250-450

Strawberries

# Light HoursLight Intensity
(umols)
Propagation12-20250-450
Vegative12-20 250-450
Flowering<12 250-450
Fruiting12-20 250-450

Tomatoes

# Light HoursLight Intensity
(umols)
Propagation12-20250-450
Vegative12-20450-700
Flowering12-20 450-700
Fruiting12-20 450-700

Where To From Here?

Notice how I mentioned the number of light hours needed for plants in the tables above? Different plants need different lengths of light exposure. You can’t just leave your grow light on 24/7! The next post in this series is How Long Should My Hydroponic Lights Be On? It explores Daily Light Integral or DLI, the measurement that takes into account growth light strength x time its on for optimal growth.

Beginners Guide To Hydroponic Lighting has a list of all our posts on lighting, written to help a beginner learn the basics and get started right through to more advanced topics.

Do I Need Grow Lights? is the previous step in this series. Not everyone has a PAR meter or Quantum meter; they can be expensive. So how else can you measure the light your room gets? Whilst not very accurate, this can give you an idea of how bright your rooms are; helpful in finding out if you need to invest in a grow lamp!

How Long Should My Grow Lights Be On For Hydroponics? is the next step in this series. You know how bright your light should be, but how long should it shine? Plants need time to sleep and rest too, just like you. This post explores how to determine how many hours of light your plant needs (it can vary a little depending upon how bright your light is).