All plants in a single reservoir share the same nutrient solution. A smart combination is therefore more important than growing as many different plant species as possible. pH indicates how acidic the solution is; EC gives an indication of the total amount of dissolved ions. EC does not show whether the proportions of individual nutrients are correct.
Target ranges by crop
Oklahoma State University publishes the ranges below for hydroponic growing. They are a starting point, not an automatic setting for every cultivar or growth stage.
| Crop | EC (mS/cm) | pH |
|---|---|---|
| Basil | 1,0–1,6 | 5,5–6,0 |
| Lettuce | 1,2–1,8 | 6,0–7,0 |
| Tomato | 2,0–4,0 | 6,0–6,5 |
Basil: pinch out regularly
With its compact root zone and rapid regrowth, basil works well alongside leafy crops. Do not harvest only individual large leaves: cut a stem tip just above a pair of leaves to encourage branching. Leave enough space between plants, as dense foliage reduces airflow. A strong aroma and compact growth also require sufficient light.
Cut-and-come-again lettuce: cool and consistent
Cut-and-come-again lettuce can be harvested leaf by leaf as long as the growing point remains intact. Start with the outer leaves and leave the heart in place. Lettuce has a lower EC range than tomato and therefore often pairs better with basil and other leafy greens. Brown edges on young leaves can have several causes, including calcium transport, high temperatures and insufficient airflow; simply adding more nutrients is not necessarily the right solution.
Compact tomato: more light and support
Choose a cultivar specifically described as compact or dwarf. Tomato needs more light, physical support and generally a stronger nutrient solution than leafy greens. Indoors, flowers may benefit from gentle vibration or airflow to aid pollination. Check the plant's eventual height on the seed label and place heavy fruiting crops lower in the tower.
Why tomato and lettuce are not a natural match
The published EC ranges barely overlap. A nutrient strength that is low for a mature tomato plant may already be high for lettuce. A mixed tower therefore requires a compromise that is not optimal for either crop. For more predictable management, group plants with similar needs or grow fruiting crops in a separate cycle.
How to measure without false precision
- Measure the source water first, followed by the mixed nutrient solution.
- Calibrate pH and EC meters according to the manufacturer's instructions.
- Record readings, water level and plant response at consistent times.
- Make corrections in small steps and follow the dosage instructions for the nutrient product you use.
- Do not assess one number in isolation: temperature, light, root health and leaf symptoms are all part of the picture.