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Frequently Asked Questions

Frequently Asked Questions

This article provides a list of frequently asked questions with a brief answer to act as a problem solving document to help you overcome general grow room and plant problems.

Roots zone, tank and growing media

1 - The plants roots are not growing out their rockwool cubes – Most likely cause is that the plant has not been established well enough before planting. This is then followed by over-watering which creates poor root growth. This is a very common problem with NFT growers.  

2 - My roots have turned an off white/beige color – Normally due to over watering. Can also happen when the plant has become deficient in a nutrient through either the pH being out of range or excessive heat coupled with low humidity. Calcium deficient plants often have discolored roots. Sometimes it can be a pre-cursor to the onset of a root disease, but this is less likely. Some additives contain ingredients that stain or discolor roots - e.g. humates.

3 - My Plants roots are brown/smelly/mushy – These are the signs of the latter stages of a root rot disease most likely to be Pythium. Once you have a root disease it cannot be cured. In extreme cases of over watering this will also happen.

4 - I have a green slime on roots/growing media – This is algae which grows on damp surfaces in the presence of light and nutrients. It is relatively harmless if kept to a minimum, but it needs managing. The first step would be to stopping light entry by covering the affected surface. Hydrogen peroxide will kill algae and quickly clear it up.

5 - I can see worms/maggots around the roots - If they have a clear body with a black head, they are sciarid fly larvae which eat your roots. You will also normally see small black flies around the base of the plant which will be laying eggs. Deal with these by using sticky traps to catch the adults and fungus gnat off to kill the larvae.  

6 - Small black flies around surface of growing media/roots – Sciarid flies, see 5

7 - There are jumping insects on the surface of the water/growing media – These are harmless insects called ‘springtails’. Treatment is unnecessary.

8 - There is an oily look to surface of nutrient solution – This is calcium nitrate in high concentration in the solution. Relatively harmless if the tank is changed regularly.

9 - My pH is decreasing during early flower – This is quite normal nutrient uptake for a plant that is undergoing a developmental change from vegetative growth in generative (flowering) growth. Adjust back up to keep in range using silicon or ph Up (potassium hydroxide) and no problems will occur.

10 - My pH is decreasing rapidly – This could be a fungal infection; either a root rot disease or even botrytis.

11 - The nutrient strength (CF/EC) is increasing rapidly – This is commonly due to the plant undergoing high levels of transpiration caused by low humidity and/or high temperatures. Just add water to bring the nutrient strength back to desired level. If using a growing media check for salt build up and consider flushing.

12 - My nutrient strength (CF/EC) is decreasing – Caused by plants with high nutrient demand. Can come about when hydroponic systems are working to their optimum level. Add more nutrient to bring up to the desired level

13 - There is a sludge or snot like substance in/on nutrient solution – This is caused by beneficial bacteria and enzymes in the solution proliferating. Can happen when additives containing bacteria are overused or when different additives are mixed. Sometimes this problem can be due to algae (see 4).

14 - There is a slime-like substance on pipes in nutrient tank – See 13

Plants and leaves

1 - All the leaves are limp and wilting – most commonly due to under watering, but can also be cause by over watering. If temperatures are too high (above 30ºC) and/or the humidity is too low (below 40%) wilting will also occur.

2 - All the leaves are going an even pale green/yellow on my young plants – normally caused by under feeding, start feeding or increase the nutrient strength.

3 - The leaves are going an even pale green/yellow on my mature plants – If this happens in the first few weeks of flowering and is usually a sign of over feeding in which case you should decrease the nutrient strength. This can also be underfeeding if in late vegetative or mid flowering stages-  see 2 and 7

4 - My leaves are going yellow but the leaf veins are still green – This is caused by a (magnesium) Mg deficiency if it’s on the older mature leaves. To correct foliar spray with Epsom salt solution (1 teaspoon to 1 liter) If its only on the new younger leaves it is an Iron (Fe) deficiency which is normally caused by high pH of nutrient solution.

5 - The leaves are turning a purple color- Most commonly cause by low temperatures and often happens in winter or with outdoor grown plants. Can also be a phosphorus deficiency but this is less common.

6 - My leaves are very dark green and brittle/leathery – a classic symptom of over feeding. Reduce the nutrient strength.

7 - My Leaves are pale green and very soft velvety – usually a sign that you are underfeeding you plant. Increase the nutrient strength.

8 - A few top leaves have very pale/burnt patches on them – Usually caused by the lights being too close and burning the leaf tissue.

9 - The leaf tips are curling under- most commonly a sign of over feeding. See also 6 and 10

10 - The Leaf tips appear burnt – classic sign of over feeding, (see 6 and 9)

11 - The Leaf margins/edges are rolling up – when the leaves do this they start to look like tubes and is a sign that they are trying to stop water loss. This mean that the humidity may be to low, the lights are too close, the temperature is to high or there is too much air movement around the plants (wind burn).

12 - My leaves are distorted/curly/mutated but not burnt – can be a sign of Calcium (Ca) deficiency, also see 14

13 - The leaf stems are turning red–This can be a variety of minor issues that you should not worry about. Most commonly it is a stress response, happens allot when plants have not been hardened off properly. Can be cause by night and day temperatures being to far apart. Some plant varieties will always have red stems. It can also be a sign of under feeding if it occurs during aggressive growth stages.

14 - I can see orange-brown rusty spots with dark outline on the older leaves between veins and on leaf edges – Classic sign of Calcium deficiency which can be caused by prolonged periods of high or low humidity, very common in soil and coco. To correct spray with calcium rich foliar spray.

15 - There are rusty patches spreading up the plant – can be over feeding (see 6,9 and 10) or calcium deficiency (see 14)

16 - My leaves have random brown patches/blotches on leaves – If the patches/spots do not have a dark outline (see14) then could be a leaf spot fungus. Treatment is difficult but can be achieved through spraying or sulphur vaporization. Cultural and environmental practices should be addressed. 

17 - There is slug like silvery marks on my leaves – caused by plant eating insects called thrips. Check on underside of leaves for larvae (see 19), Control can be achieved through spraying and/or the predators.

18 - There are loads of white/yellow dots on the leaves – caused by spider mites check for small insects on underside of affected leaves. Control can be achieved through spraying and/or predators.

19 - Small worms/maggots on leaves – thrips larvae see 17

20 - I have water drops on leaves edges – Usually noticed when light just come on. Happens after dark period when growing media is wet and humidity is high which causes water to leak out of leaf edges (process is called guttation). Can also happen when growing media is wet and humidity drops when the lights go out. When leaves overlap each other water can also collect on the lower leaf.

21 - There is a white powder/dots growing on the leaf surface – this is a fungal infection called powdery mildew. Increase ventilation and air movement and use a spray with activity against fungus.

22 - My plants stunted plants with no growth and the leaves appear wilted – These are the symptoms of a vascular plants disease called Fusarium. Plants will not recover, confirmation can be obtained when the stem is cut in cross section and a brown ring is visible.

22 - Leaves on the plant are drying, the edges are burning and the stems are woody – Symptoms of wind burn which is caused when too much air is moving around the plants. Happen if you point a strong fan at a plant, always point circulation fans away from plants and towards the walls of the room.

23 - The Flower tops are stretching out – this happen when flower sets get heat stressed, usually remedied by raising lights or using a heat shield. Can also happen if the dark cycle interrupted, never go in your room when the light are off.

24 - The leaflets around flowers are turning yellow– Usually a sign of a botrytis/bud rot infection. Gently open the flower set to see if grey mould is visible. Remove any infected flowers immediately, treat other plants with a spray with activity against fungus .

25 - I can see fury grey fuzz/mold in flowers – botrytis/bud rot infection (see 24)

26 - My Flower sets are stretching/airy not dense – Most likely that the plant is not receiving enough fresh air (Co2). Can also be heat stress related (see23) and also under feeding.

27 - My plants won’t flower and have stretched and elongated stems– Happens if the light cycle is interrupted during dark period, never go in your room when the lights are off, check for any bright L.E.D’s on equipment inside your room.

28 - My plants seem too big and leggy – very common in summer, happens when temperatures are too high. Can be a sign of not enough light but very uncommon. Some plants are naturally big and tall which are unsuited for indoor growing.

29 - The plants are stunted/stopped growing and the leaves discolored – possible disease, normally associated with Pythium (see Roots section, 3)

Cuttings and Seedlings

1 - My Cuttings won’t root – This is a very common question and can be due to a number of factors.

  • The most common is the growing media you are using is being kept too wet. If you are using rockwool, after pre-soaking shake the cube to expel the excess water within the cube. When you spray your cuttings spray the foliage lightly not the cubes. Never leave water standing in the bottom of the propagator.
  • Cuttings will take a long time to root if they are too big, try to take smaller cuttings around 3” (7-8cm) and remove big leaves from the cuttings to reduce leaf surface area.    
  • Check you rooting hormone is still in date
  • Do not use strong nutrients to pre soak cubes with as this will inhibit root formation.
  • Make sure the temperature is between 18-24ºC and is kept fairly constant. If your temperature falls more than 4ºC between day and night keep you lights on continuously to maintain a constant temperature.
  • Make sure you use a propagator and the vents are closed until roots appear.
  • Be patient, the average time to root cuttings is 10-14 days.   

2 - My cuttings are wilting – Can happen soon after taking the cutting but they should come back around. If they stay wilted its usually a sign temperatures are too high (common problem in summer months). Reduce temperatures in the propagation area.

3 - The base of the stem on seedlings/cuttings brown/black/rotting – This happens when the growing media is kept too wet which invites fungal diseases to attack the plant collectively know as ‘damping off’ diseases. This is particularly problematic in warm and wet conditions.

Other Problems

1 - I’m experiencing over feeding problems but nutrient is within range – the first thing to do in this situation is to calibrate your pH/CF meters as they could be giving you incorrect readings. It could be a nutrient salt build up in the growing media in which case you will need to flush your growing media. If your temperatures are high and humidity is low you plants will have a high transpiration rate which will cause them use more water and less nutrient which will cause a salt build up to happen. You could be suffering from wind burn which can look like nutrient burn.

2 - My Yield has gone down – The hardest thing in horticulture is to replicate consistent results and there are so many variables. The first thing to consider is that are all variables the same?

  • Plants variety is the obvious variable that can considerably change yields.
  • The environmental conditions are very important and will nearly always differ between crops (max-min temps and RH).
  • HPS Lamps need replacing every 9-12 months to maintain good light output and over time yields will go down if lamps are used for too long.  
  • More is not always better so address the amount of nutrient you are using and the amount of additives that are being used or overused.

Equipment Problems

1 - My light keeps blowing timers – All H.I.D lighting units that run high pressure sodium or metal halide lamps draw a lot of power when they start up so cannot plugged straight into a timer. You need to use a contact relay which will start you lights up without drawing a large inductive load through the timer.

2 - My ballast is making a loud buzzing noise – make sure bulb is screwed in fully and i.e.c connectors are pushed tight together, if unit is old consider replacing.

3 - The pump is on, vibrating but not pumping any water – this mean that the pump is either air locked or the filter is blocked. If your submersible pump is air locked you will see a group of air bubbles leave the pump when to turn it upside down under water. If your pump has an internal filter then they need cleaning every few weeks by rinsing in clean water.   

4 - Smell is leaking out of my grow room – This happens when you room has a positive air pressure created when you have more air coming through your intake fan than being removed through the exhaust. To combat this you need to decrease intake and increase your extraction. Remember: if you use a carbon filter it will reduce the efficiency of your fan by up to 25%.

5 - My drippers keep clogging up – This normally only happens when the additives being used (beneficial bacteria, enzymes, silicon,) are causing a salt build up or bio sludge to block the dripper outlets. It is more common in hard water areas where carbonates in the water will calcify on the drippers. Using House & Garden Drip Clean will help prevent sat build up on drippers. Some dripper blockages are caused when there is not enough pressure in the drip lines so consider upgrading the pump.

6 - My ventilation system is too noisy– Fist thing you need to establish is where the noise is coming from. If it’s the fan motor then all you can do is add padding around it or make and insulated box for it or upgrade to an acoustic fan. Most noisy ventilation systems are caused by the movement of high volumes of air through ducting which can be reduced by making sure ducting is straight and smooth. Consider acoustic ducting or using a fan speed controller to slow fan down

7 - My carbon filter is not working – This happens when the humidity runs too high, above 75% the activated carbon will not be work effectively. Remember that most activated carbon has a life span that ranges between 6 to 18 months so if it has been in use for a while and has stopped working then it may need replacing.


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