System clean-up between crops
Do not under-estimate the need for post harvest clean-up. Failure to do this properly can result in ongoing problems from disease, plumbing blockages and broken pumps.
Do not under-estimate the need for post harvest clean-up. Failure to do this properly can result in ongoing problems from disease, plumbing blockages and broken pumps.
Two separate precautions should be taken to ensure hardware is clean prior to replanting:
At the end of each crop it is necessary to sterilize the entire system to help prevent disease problems in the next crop.
Step 1. Remove plants and medium from the system then do as much manual cleaning as possible. External cleanliness of the system and growing area is as important as internal.
Step 2. Partly fill the reservoir with water. Lower the water’s pH to between 4.5 and 5.5. Then, after providing good ventilation for the area and subdued light conditions, add household chlorine bleach** (50g/L chlorine) at ~5ml per litre (4 tsp per Gal).
Step 3. Mix well, then soak system for 24 – 72 hours. While the system is soaking:
● Recirculating systems: Run the pump for at least 15 minute cycles every hour^.
● Run-to-waste systems: Run the pump for a short burst once every hour^.
Step 4. Discard this solution then flush the whole system several times with small volumes*** of fresh water to remove all traces of chlorine and dislodged material.
^ Note that there must be adequate ‘contact’ time (e.g. minimum of 24 hours) between the chlorine and all surfaces e.g. system sidewalls, pipes, etc. Pay particular attention to areas where there is usually zero water flow, such as dead-spaces in taps. ‘Flooding’ may be necessary to contact hidden surfaces e.g. underneath the upper surface of channels.
Also, note that chlorine bleach will not dissolve algae or general solid material. Only wet brushing will remove those contaminants.
*** Several small volumes are more effective than a single flush.
Step 5. Where fine drippers and sprayers are used, it may be necessary to individually dismantle and clean each unit.
** Avoid contact with metal parts and ensure to follow necessary safety precautions. Use protective clothing (e.g. mask, goggles, gloves).
When sidewall deposits become significant, they can harbour disease and also cause blockages if present in plumbing lines.
An acid flush can be effective for removing precipitates of salts such as calcium sulfate (Fig 12.4). These generally cannot be dissolved with plain water or wet brushing:
Step 1. Add water and enough hydrochloric acid** to the reservoir to achieve pH 2. If using rain or RO water, dilute 30% hydrochloric acid (normal commercial strength) by around one-thousand fold i.e. 1ml per litre (3/4 tsp per Gal).
Step 2. Soak the system for 24 – 72 hours. While the system is soaking:
● Recirculating systems: Run the pump for at least 15 minutes in every hour.
● Run-to-waste systems: Run the pump for a short burst once every hour and collect the discharge.
Step 3. Afterwards, neutralize the flushing solution to pH 5 – 6 with soda ash before discarding.
Step 4. Flush the whole system several times with fresh water to remove all traces of acid and dislodged material. Ensure the pH of the final washings is above 5.0.
Step 5. Where fine drippers and sprayers are used, it may be necessary to individually dismantle and clean each unit.
** Avoid contact with metal parts and ensure to follow necessary safety precautions. Use protective clothing (e.g. mask, goggles, gloves). 30% hydrochloric acid is volatile (emits significant fumes) therefore decant in the open air. Also, because this chemical is highly volatile and corrosive, store it in a well ventilated area.
SYSTEM HYGIENE: Discarding old nutrient solution | Flushing root zone