Why do Japanese Buxus leaves change colours?

[d23]

Hi there,

I'm needing some advice to understand what the colors of the the Japanese Buxus leaves mean as they change.

Some history to the images:

- I have the buxus in full sun, next to fence above the pool tiles

- Pots are fibre glass, black, have bitumen lining and drainage holes, off the ground, plenty of soil - used Jeffries veggies and garden soil

- Had them for about 2 years now so not fully mature yet

- I did use Jeffries Forever Black Mulch, for last 2 years, but have since realised its taking nitrogen from the soil etc and have last week replaced with Jeffries Recover mulch instead

- I've used fertiliser on the leaves and soil in spring - Powerfeed and others such as Plant Doctors seaweed with humic and fulvic acid, Activ8mate and Qauntum H. Use liquid iron but not a huge amount.

- I'm trying to understand the soil moisture levels better - at the top it seems dry, half down OK, deeper it looks wet - when digging down the soil itself seems dry but is warm/moist - would this be because the pots are black and the area is hot from the tiles and fence vs actually being moist - i.e. a false positive - I'm wary of overwatering but could I be underwatering especially in recent hot weeks (based in Adelaide)?

My question: Last summer I saw the same process, where the leaves start to brown like the photos and then turn to a yellow crisp eventually some of the leaves dying - what nutrients (if any) am I missing that's not keeping the leaves green and healthy? Or is this normal for this aged of buxus to go through?

Thanks so much

[MitchellMc]

Welcome to the Bunnings Workshop community @d23. It's marvellous to have you join us and many thanks for your question about growing Buxus .

I'd suspect they are likely getting burnt and under-watered. You have a steel fence behind them and black pots. The pots would become scorchingly hot during Summer and the fence would be radiating heat onto the foliage. Can you place your hand on the pot during the middle of a hot summer's day and keep it there for any amount of time (careful not to burn yourself)? I'd imagine not, now think of how hot the roots must be getting.

I wouldn't pay much attention to those moisture meters. I've never really had great success with them myself. Just stick your finger in the pot. If it's dry, give them a good 10 mins soaking and then don't water again until the soil is dry to your finger again. On hot summer days, you should get out there and give them a midday watering and possibly another in the afternoon.

Buxus leaves can brown off over winter, but this is likely to do with watering/heat. Also, instead of playing with different fertilisers, just stick to a slow-release complete fertiliser like Osmocote All Purpose.

Please let me know if you have any questions.

Mitchell

[d23]

Hi Mitchell,

Thanks for the reply, truly appreciated.

Yes it absolutely gets scorching hot on hot days - I've been worried about over watering them based on the moister meter and the soil being a little moist deeper in the pot. I got a electrical conduit yesterday and took a few samples all the way to the bottom, generally it was dry (and needed to force some of the conduit in) but the bottom was a bit more moist and clumped.

I did a good deeper water last night to check drainage....drainage is all good, infact on a couple of boxes I found the water wasn't absorbing well and flowing straight out so I assume the soil has become a bit hydrophobic and when watering its been going down the side of the pots making the bottom of the soil moist but not through the soil properly. 

I'll re water once the top 2 inchs become dry again - is there any wetting agent etc I should add if this is the situation?

Thanks again

 

[MitchellMc]

I would consider all that soil sample to be "dry" and the plant needs water. I think you'll find you need to water at least twice a week in Summer and a good soaking at that. If you soak the plants (spending 1-2 minutes on each), the soil will absorb the water. I don't feel the soil is necessarily hydrophobic; it just needs to be watered adequately.

Try some Seasol 2 x 2L Hose On Super Soil Wetter And Conditioner. It will add a soil wetter, and the tonic portion will assist with the plants recovering.

Mitchell

[robchin]

Hi @d23 

As @MitchellMc  has suggested I think the plants are just getting too hot in the sun. Remember that Box plants come from Europe and Asia where the summers don't typically get as hot or as bright. The advice on the fertilisers is good as well. I also don't believe that your mulch will be taking Nitrogen from the soil because it looks like a hardwood mulch so no risk of nitrogen drawdown there. Use the soil condition/wetting agent as suggested and just accept that you will get a loss of colour in the hot weather and possibly the cold weather.

Final point I would make is that plants in pots/planters will seldom do as well as plants planted directly into the ground. There is a finite amount of space for the roots to grow into and the amount of soil moisture that can be held. 

I know, given the location of the plants/planters it will be difficult but given these plants are always going to be hot and dry in summer - my best suggestion would be to install a watering system into the pots using a micro-trickler system. You can click a hose onto it when you want to water. Have a look at this DIY video for instructions https://www.bunnings.com.au/diy-advice/garden/water-irrigation/how-to-install-irrigation-sprayers-an...  and use this trickler as the emitter - use 1 in-between every 2nd plant. Once installed adjust them for a slow drip.  https://www.bunnings.com.au/pope-adjustable-flow-trickler-on-spike-10-pack_p3120455