Lettuce cultivation exponential growing experiment


Growing lettuce at Quinta Vale da Lama, a Soil Food Web Trial in Fall 2023

During this fall, a 6-week field experiment has been running on the farm – Quinta Vale da Lama – in order to measure soil improvement and agricultural production gains through working with soil biology. The objective was to show how the addition of good soil microbes through worm castings extracts can improve agricultural production.

The methods

On September 21st 2023, 96 seedlings of lettuce from our greenhouse were planted in the soil, next to our worm-compost station. 

Biology was applied to the treated lettuces by soaking the seedlings before planting, at planting and then weekly until the harvest.

The treated plots of lettuce received weekly applications of extract made from 3 kg of fresh worm castings that were soaked and stirred for 5 minutes into 15 L of water. The control lettuce received an amount of water similar to the amount of extract applied, to prevent differences in soil moisture.

Different parameters were measured in order to evaluate the impact of the treatment on the lettuce growth (height and diameter of the leaves, root development and plant weight) and on the soil biology (microscopic analysis).

The results

Weekly, biology assessments of the extracts were taken by microscopic analysis in order to verify the quality of extracts which is essential to ensure soil biology improvements and agricultural production gains when working with soil biology.

After 6-week of lettuce growing, all the lettuce were harvested and numerous measurements were made on the same day (November 1st, 2023): height and crown diameter, root depth and plant weight. Although the treated salads were ready for market, the control would have had to remain in the soil for a minimum of two more weeks before harvest. However, for the purpose of comparative measurements all were taken out at the same time. 

The difference between the control and the treatment was considerable as can be seen in the results (photographs and graphs):

  • Lettuce weight: treatment was on average 219% heavier (250gr. vs 114gr.)
  • Lettuce height: 24% higher (21,8cm vs 17,6cm)
  • Root depth: 40% deeper (9,5cm vs 13,3cm)
  • Crown diameter: 43% wider (34.1cm vs 23,8cm)


This field experiment showed significant results on how the addition of good soil microbes through worm castings extracts can improve agricultural production. 

Easily you can make a HUGE difference in garden productivity with very little work: by applying a compost extract from your own compost. It is fundamental to make sure that the quality of your compost is good enough and it needs first to be evaluated.

Elodie da Silva
Experiment design and article
Jeroen Boss
Experiment and photo credits

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Written by: Elodie da Silva and Jeroen Boss

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