Hydroponic Lettuce Experiment - Week 4

Introduction

The past two weeks presented a significant amount of changes to the lettuce plants:

• Two new generations of leaves have grown
• Plant roots have gained root hairs and begun to curl
• Nutrient solution was added
• Additional discolourations appeared on several leaves

Observations

Each lettuce plant has grown two new leaves. New leaves appear to be more wavy and curled than the previous generation. When leaves grow, they develop at the stem of the previous leaf. They eventually separate rolled into a cylinder. Over time, the leaf-coil unrolls into a proper leaf. Fig. 1 shows the growth of lettuce plants over time in photos.

Fig. 1 - Lettuce plants on various dates (from top to bottom, left to right: May 21, 22, 23, 26, 27, and 31.

Until recently, the roots have been growing relatively straight. Presently, they are slightly curved at the base. This likely results from the roots reaching the bottom of the hydrogarden reservoir and, therefore, is not considered to be an issue. Root hairs are also growing and measure 5 mm at the longest. Fig. 2 shows an image of the roots.

Fig. 2 - Lettuce roots on May 27. Note the end-curl and root hairs.

On May 26, 105 mL of stock nutrient solution (Schell-Toogood v.1) was added because a large quantity of it was used and/or evaporated. By knowing the original amount of solution and the number of days passed, one can produce this formula for nutrient solution evaporation:

, where V₀ is the volume of solution at t = 0.



In more understandable terms (or less, depending on how you see it), nutrient solution evaporates at a rate of 7.8 mL/day. It should be noted, however, that this assumes that evaporation is a linear process.

On May 19, discolourations on the tips of two leaves from the first generation were discovered. Eventually, similar discolourations began occurring on all first and second generation leaves. As of May 28, they did not appear to be progressing further. It is unknown whether it is a natural part of the growth of a lettuce plant or if it was caused by an environmental factor (e.g. lack of nutrients). Fig. 3 shows these discolourations.

Fig. 3 - Tip discolourations on some of the first generation leaves (Left: May 23, Right: May 26)

Fig. 4 shows the length of the lettuce plants and their roots over time. Data for May 21 and May 28-30 has been interpolated because measurements could not be made on these days. It appears that a plant height recession occurs before a new leaf separates from the main stem. After a recession, plant height increases to a greater height than before the recession.

Fig. 4 - Graph outlining the height of lettuce plants and roots over the past 4 weeks. Quick, what do lettuce plants and capitalism have in common?

Conclusion

Week 4 marks some significant growth and changes in the lettuce plants. Plants show signs of maturing, such as developing root hairs and general upward growth, as well as regression, as seen in leaf-tip discolourations.

Several observations require additional examination:

• The evaporation equation must be tested to ensure it is accurate in predicting the volume of nutrient solution.
• The spread and intensification of discolourations on first and second generation leaves must be monitored to ensure they do not result from a nutrient deficiency or other health issue.

In the coming weeks, I hope to gather enough data to find patterns that will give insight into the growth of lettuce plants.

Hydroponic Lettuce Experiment - Week 2

Introduction

On May 5, 2013, I planted some lettuce seeds in my simple hydrogarden set-up in the hopes that something would grow. I have attempted similar experiments some months ago, but they were dismal failures. This experiment, on the other hand, appears to be at least somewhat successful thus far.

The purpose of this experiment is to gain some insight on how plants grow in a hydroponic environment. I need this information because I am not very familiar with growing plants without soil (or even with soil). Because of the philosophy of this experiment, it is not a true experiment, but rather an all-out test performed with some scientific principles.

It should be noted that no automated components are currently in use.

My hydroponics rig, as stated previously, is quite simple. It contains the following components:

• 473 mL plastic container
• Schell-Toogood v.1 nutrient solution
• Sponge (inert medium)
• Aquarium pump
• Lindenburg "Grand Rapids" lettuce seeds (Lactuca sativa).

You may have noticed the material called "Schell-Toogood v.1 nutrient solution." This solution was created by my chemistry teacher and I and it provides all nutrients necessary for plant growth. It is a slightly modified version of the PrometheusWiki's version of Hoagland Solution. If the solution is successful, I may write a more detailed explanation of what it is and how to create it.

For each day that the experiment is active, I will record the height of the plants and the length of the roots, the overall condition of the plants (especially any notable changes), and any alterations to the hydroponic system (e.g. replaced nutrient solution, turned off aeration pump, etc.).

Observations

Fig. 1 shows some pictures of the lettuce plants at various days throughout the experiment. The lettuce appears to be pale green in colour, but this may be due to the type of lettuce rather than resulting from any nutrient deficiencies. Additional observation and research are required to make any definite claim.

Fig. 1 - Lettuce plants on May 9, 15, and 18, respectively. Note the growth of additional leaves.

I also noticed a slight discolouration on one of the leaves (Fig. 2). Whilst it does not appear to be spreading, it does appear to be impeding the leaf's growth.

Fig. 2 - Lettuce leaf with discolouration on May 9 and 18, respectively.

Fig. 3 shows the growth of the lettuce plants in chart form. A trough in plant height occurs on May 17. My experiment journal claims that the plant appeared to be wilting on that day; as a result, the nutrient solution was replaced. However, it is unclear if the plant was indeed wilting or if it was spreading out to accommodate for new leaves.

Fig. 3 - A chart outlining the growth of both the lettuce plants and their roots over the past week.

Conclusion

Fig. 4 - A not-as-successful attempt at growing hydroponic lettuce.

This current attempt at growing plants hydroponically is much more successful than previous attempts have been (Fig. 4). In the last two weeks, lettuce plants have germinated and grown to a respectable height.

Several observations were made that require additional examination:

• Plants appear pale green, which is a sign of malnourishment, but this may simply be the nature of this particular type of lettuce.
• A discolouration was found on one of the leaves which should be kept in mind.
• A period of wilting may have occurred on May 17, although this may have been caused by leaves being spread out to allow new ones to grow instead.

I plan to do blog posts similar to this on a weekly basis every Sunday. Each post will contain my observations for the week and some analysis on it.