Correctly plan supply air routing in the earth grow room

## Introduction

Air supply** is often underestimated in indoor soil cultivation. Many growers pay a lot of attention to exhaust air and circulating air, but fresh air that is too cold, too dry or flows in too quickly can easily cause **local climate problems**: Draught stress, cold root areas at the pot, uneven humidity and strong differences between edge and center zones. A calm climate is particularly important in soil, because although the substrate buffers nutrients, it only reacts indirectly to recurring climatic stress. The aim is therefore not simply "lots of fresh air", but an **evenly introduced, plant-compatible supply air**.

## Why supply air management is a climate issue in its own right

Supply air influences several climate factors at the same time:

- **temperature** of the incoming air

- **relative humidity** after the air exchange

- **CO2 supply** in the room

- **air flow** in the area of pots and canopy

- Stability** between day and night phase

Poorly managed supply air often does not cause any immediately visible total losses, but it does promote:

- uneven growth

- dry leaf edges due to continuous draught

- cold, damp corners

- locally increased risk of mold

- strong fluctuations after each exhaust air cycle

## Special features in soil cultivation

In Soil-Grow, water evaporates not only via the leaves, but also moderately via the **substrate surface**. After watering, the humidity often rises temporarily. At the same time, soil stores heat better than coco or hydro media, but reacts slowly. For this reason, air should be added to the soil grow **gently and evenly** instead of in hard spurts.

It is also important to note that too cold air applied directly to fabric pots or plastic pots can lower the **root zone temperature locally**. This is particularly problematic if the soil is cooler after watering anyway.

## Choose the right air supply source

Ideally, supply air should come from an area with **clean, preferably stable ambient air**. Avoid air from rooms with strongly fluctuating humidity, dust, smoke or large temperature peaks.

The following are suitable:

- Adjacent indoor rooms with a moderate temperature

- Pre-filtered fresh air from a climatically stable area

- passive supply air only for small, easily controllable setups

Less suitable:

- very cold outside air without mixing or preheating

- hot attic air

- humid basement air with risk of mold

## Inlet position without draught stress

Supply air should **not hit plants or pots directly**. It is better to have an inlet that first directs the fresh air into a free zone so that it can mix with the room air.

Proven to be effective:

- Inlet **below the canopy**, but not directly at pot height

- Lateral introduction against a wall or tarpaulin

- Use of air hoses or deflectors to defuse the air flow

Avoid:

- direct air jet onto young plants

- Supply air directly onto the ground surface

- Inlet exactly opposite a strong exhaust air, if this creates a short-circuit flow

A **short-circuit flow** means that fresh air is immediately drawn into the extract air without effectively mixing the room. This leaves edge zones climatically unstable.

## Temperature control and humidification or dehumidification of supply air

The supply air does not have to have exactly the same values as the room, but should not have any extreme deviations. The following applies in practice:

- Warm up cold supply air in the anteroom beforehand or mix it with room air

- Do not blow in very dry supply air unchecked

- Only supply very humid supply air with sufficient dehumidification capacity

A **stable humidity control** is particularly helpful for earth-grown products, because watering days can already increase the RH. If additional humid supply air flows in, critical zones develop more quickly.

## Guide values by phase

### Young plants and early vegetation

- Temperature: **22-25 °C**

- Relative humidity: **60-70 %**

- Supply air only gentle, without direct flow

### Vegetative phase

- Temperature: **22-26 °C**

- Relative humidity: **55-65 %**

- even distribution of fresh air, no dry peripheral zones

### Flowering phase

- Temperature: **20-26 °C**

- Relative humidity: **40-50 %**, in late flowering rather **40-45 %**

- Supply air in such a way that no moist pockets remain in the crop

### Drying phase after harvest

- Temperature: **18-22 °C**

- Relative humidity: **about 60 %**

- Air exchange gently, without blowing directly on the buds

## Control in practice

Don't just check one central measuring point. Measurements are useful:

- at the supply air area

- at crown height

- in the edge area opposite the inlet

- near pot height, but not directly on the substrate

Look out for the following warning signs:

- Plants at the inlet develop smaller

- Leaves show curling on one side or dry edges

- Pots at the inlet cool down more

- RH drops abruptly after air exchange and recovers slowly

- Individual corners remain permanently moist

## Conclusion

Good air supply makes the grow room **more even, quieter and more predictable**. This is particularly worthwhile in soil cultivation because stable temperature and humidity conditions relieve the plants and indirectly protect the substrate climate. The decisive factors are **draft-free introduction, sufficient mixing and suitable conditioning of the fresh air**. In this way, you avoid local climate stress zones instead of just optimizing the average value in the room.

## Pro Tips

- Never direct supply air directly onto pots or leaves.

- An anteroom stabilizes cold or dry supply air.

- Always check the climate at several measuring points.

- Allow for an increase in moisture after watering.

- Late flowering requires particularly dry marginal zones.