Rocket cress can be used as an indicator crop

Greenhouses are supposed to create ideal circumstances for production of vegetables and flowers. But sometimes growers are surprised that crops do not really grow that well or even show damage. Toxic air can be one of the causes:

• Harmful substances in fumes from a malfunctioning boiler or CHP.
• Harmful fumes when firing newly painted heating pipes.
• Vapor from new screening material.
• Harmful fumes from a newly poured concrete path.
• Strange smells, unwanted air from new tubes on heating pipes.
• Or if the entrepreneur's son is tinkering with his moped in the warm boiler room, after which the exhaust gases go into the greenhouse via the burner or the CO2 ventilator. 

Rocket cress quickly indicates whether or not there are toxic substances in the greenhouse air. Mostly way before the tomatoes or other crops show traces of damage from toxic air.

1. Sow a quantity of cress in different places on the rockwool layer, or in trays with moist soil or a layer of moist paper. Don’t rely on just one place in your greenhouse but create multiple test points.
2. Sow in the greenhouse and also put a few trays in a place where no suspicious smells can come. This is for comparison.
3. If the air contains toxic substances, normally the cress shows damage in one or more days.
4. Repeat this test a number of times, 2 times a week is customary.
5. In some situations it makes sense to sow the seeds a few days in advance. The cress is then placed in the greenhouse as soon as, for example, the first flue gases are allowed in, or as soon as the pipes are fired for the first time. After a day, the result is often already visible.

If the rocket cress shows damage you know the air is suspicious. The next step is to find out which substance causes the damage. Please note that an incorrect nutrient solution or contaminated rock wool will also lead to damage to cress. Crop damage can also be caused by other things. Our colleagues at Hagelunie can inform you further about the use of this indicator.