Troubleshooting Guide for Growing

Even the best growers run into problems - lets help you troubleshoot common issues!

This guide helps you quickly diagnose common symptoms, identify the likely cause, and take the right first actions – with further steps if the issue continues.

Lights

• My light hasn’t come on?
  • Check connections and equipment. Correct obvious faults like loose plugs.
  • How old is your lighting system – you may need to replace ballast, lamp, or reflector.
  • Check lamp fitting and visible damage – replace lamps if needed.
  • Check 13A plugs and fuses – replace if blown.
  • Try another lamp – if that works, replace the faulty one.
  • If under warranty, call 0333 003 2295 for exchange or repair.
• My light has stayed on?
  • Timer may be fused in the “on” position.
  • Use a relay or contactor with high-output MH & sodium lights (400–1000W). More modern LED lights don't need a contactor due to 'soft-start' and other features, but we would always recommend one for safety and peace of mind.
  • Upgrade to light switching timer contactors.

Propagation

• Cuttings wilt
  • Too hot – turn heated propagators down, or use timers or temperature controllers.
  • Move propagator further from light, or open vents more.
  • Monitor with a thermometer.
• Damping / rooting issues
  • Too wet – spray less often, ensure media isn’t saturated.
  • Remove standing water in propagator.
  • First action: adjust watering. Further action: add oxygen with Silver Bullet Roots.
• Cuttings slow to root
  • Too wet – make sure clones aren’t waterlogged.
  • Too cold – use heated room or Hi-Top Propagator.
  • Old rooting hormone – replace every 3 months.
  • Cuttings too small/thin – take thicker cuttings.
  • Old tired stock – introduce new mother plants.

Leaves

• Droopy leaves
  • Hot grow room – move lights away or increase airflow. Consider extra extraction.
  • Lack of oxygen in root zone – keep tanks cool, use air stones or Silver Bullet Roots.
• Edges curling / hooking down
  • Overfeeding – flush systems or pots, then feed with a stress reliever like SuperThrive.
  • If persistent, use a cleaning solution to reset system.
• Colour lightening
  • Underfeeding – increase feed strength and check improvements.
• Edges curling up
  • Wind burn – turn oscillating fans down or reposition.
  • Lights too close – move lights a few inches away.
    
• Tip burn
  • Close to overfeeding – weaken feed slightly.
  • If also upward leaves – too hot or windburn. Lower light, adjust fans, add circulators.
  • SuperThrive can destress affected plants.
• White dots on leaves
  • Caused by spider mites, leaf miners, or thrips.
  • Manually remove badly infected leaves. Spray plants every 5 days.
  • Pyrethrum 5 EC treats most pests.

Plant Growth

• Stretched growth
  • Normal – may just need new stock.
  • Too hot – slightly move light back or cool the grow room.
  • Not enough light – move light closer, or invest in more lighting.
    

Roots

• Mushy brown roots
  • Pythium root disease – keep grow room clean with Silver Bullet Roots & Mist.
  • Control water and root zone temps.
  • Treat with Pythoff where necessary.

Nutrient Problems: Nitrogen, Phosphorus & Potassium

Before you reach for a bottle, use this rule to narrow it down: N, P and K are mobile, so the plant moves them from old growth to new when it runs short. Damage on older leaves points to a macronutrient issue. Damage on newer leaves points to a micronutrient issue.

Nitrogen (N)

Signs of deficiency

• Slowed or stunted growth across the whole plant
• Poorly formed roots, weak stems and stalks
• Older leaves turn pale green or yellow, sometimes with dark spots and burned edges
• Leaves curl and bend in the worst cases
• Disease and pests move in, because the plant is weak

Signs of excess

• Weak, stunted plants with thick, brittle, very dark green leaves
• Spindly, frail stems
• Continued vegetative growth instead of flowering
• A knock‑on potassium deficiency
• Leaf burn, turning yellow or brown

What to do

Stop any foliar feeds first. Then weaken your feed or alter the NPK ratio. If that doesn’t shift it, flush the plant, media and system for a few days, then reintroduce a weaker solution and build strength back up as the plant recovers. If you’re trying to push flowering, switch to a bloom feed.

Phosphorus (P)

Signs of deficiency

Look at older leaves for:

• Slowed growth leading to small leaves
• Small, thin stems that can turn purple
• Dark blue‑green foliage, older leaves first
• Purpling starting on the veins and leaf undersides, yellowing as leaves die
• Leaf tips that die before the leaf changes colour
• Purple or black spots spreading from leaves to stems
• Delayed maturity — slow or no flowering, limited fruit and seed

Signs of excess

Phosphorus is notoriously hard to absorb, so genuine excess is rare. When it happens it shows up as deficiencies of iron, magnesium, copper and zinc:

• Yellowing between the veins on new leaves (Fe, Cu, Zn) or older leaves (Mg)
• Leaf blades dying and curling upwards (Mg, Cu, Zn)
• Leaves turning white (Mg or Fe)
• Purple stems (Mg)
• Small leaves (Zn)

What to do

Don’t simply add more phosphorus — the cause is often too much of something else. Flush the plant, media and system and give water only for two to four days, or until you see recovery. Then reintroduce a weak feed with adequate phosphorus and build up.

Potassium (K)

Signs of deficiency

• Slowed or stunted growth across the plant
• Poorly formed roots, weak stems and stalks
• Older leaves turning pale green or yellow, with dark spots and burned edges
• Leaves curling and bending in bad cases
• Disease and pests taking hold

Underfeeding is one cause, but excess nitrogen or sodium in your solution will do it too.

Signs of excess

Too much potassium causes calcium, magnesium and nitrogen deficiencies, so look for those:

• Short, restricted plants (Ca or N)
• Pale green or yellow leaves turning purple/brown (N)
• Thin, spindly, purple/brown stems (N)
• Decaying roots, flowers and inner tissue (Ca)
• Yellow or bright green leaf edges (Mg)
• Crispy, crinkled leaves (Ca or Mg)
• Brown spots on leaves (Ca)

What to do

There’s no quick fix — adding potassium easily tips another element into excess. Flush the whole system with pH‑adjusted water for three to four days, then restart with an appropriate feed containing enough potassium, watching pH closely. Choose boosters carefully, since excess sodium drives potassium deficiency. Once plants have recovered from a potassium excess, a good CalMag will restore the calcium and magnesium it displaced.

This blog is part of our How to Grow Indoor Plants – Your Complete Guide series, designed to tell you everything you need to successfully grow indoors.