Norfolk Island Pine - Needles & Tips Gradually Dying
This is my first time posting on this site (or any site for that matter). I've appreciated some of the excellent posts I've read here.
I have a Norfolk Island Pine (Araucaria heterophylla) that someone gave to me last year. It was in need of a repotting. After some research to find if this type of plant has any special soil requirements I came across Al's Gritty Mix elsewhere on this site and decided to give it a try. I now have several plants potted in this mix (a schlumbergera, several spider plants, an aloe vera, and a dwarf schefflera) and most of these are doing really well. However the Norfolk has been suffering both prior to and after the repotting. What has been happening is that the needles on the top stem started to turn brown. Then along the sides of the plant one by one some needles have also turned brown. Lately the tips, where growth normally is observed, are turning a sort of greyish color, like something is impairing their attempted new growth. In a few places the grayish tip growth has turned brown.
The following summarizes what I have tried and how I have been caring for this plant:
- Feeding every watering (http://www.botanicare.com/Pure-Blend-Pro-Grow-3-2-4-P43.aspx) at 1 tsp per 3 liters (their recommended rate). I adjust pH of water/plant food mix to about 5.8 (phosphoric acid pH-Down) and use Brita-filtered water.
- I bought 2 humidifiers for my plants and that with humidity trays keeps RH at about 55%.
- The Norfolk is misted about 3 times per day.
- I allow top inch of gritty mix to get dry between waterings and then do a drench watering and allow the excess to drain (works out to about 1 drench watering/week).
- I bought 3 grow lights for my plants (SunBlaster T5HO, 4' 54 watt) which provides about 200 ft-ca of supplemental light in winter. I have them on for about 14 hrs/day. The Norfolk also gets partial sunlight. Total light probably ranges from 200 to 1000 ft-ca of light on an average winter day.
- Since the plants are in front of a bay window which otherwise gets cool in the winter, I have two supplemental heaters for my houseplants to keep winter temperature between 18-22 celsius (64-72 F). Heaters are radiant oil (not forced air) and put out a very gentle heat.
- A couple of times I tried adding a little SuperThrive to the Norfolk's plant food to see if that would help, but I don't think it has.
- I also tried putting the Norfolk in front of a different window but that hasn't made any difference.
- I also tried upping the dosage of plant food to 2 tsp per liter and I think (but am not sure) that the problem has got a little worse.
I'm using basically the same caring regiment with most of my plants (including the gritty mix) and they have all been doing well considering that I live in zone 3a (north-central Alberta). However I'm getting very concerned about my Norfolk. I'm hoping someone can take a look at some pictures of the plant and maybe from past experience observe what might be causing the deterioration & growth problems.