Acer palmatum Atropurpureum

Further information regarding Japanese maple question no.4 has been received (re-printed below) and I’ll clarify all the points raised.

I think this was the second summer that I had the trees. I put them in these pots, using whatever dirt was in them to begin with (I bought the apartment and the pots were on the terrace with dirt in them) - no idea what kind of soil it is. I believe the trees were close but not identical when purchased (at Home Depot). The healthy one gets more sun than the sick one – neither gets full sun. I am constantly weeding these and the other pots.

The watering system is a drip system. Both trees have 2 adjustable emitters in them, all were wide open. I had been watering them 2 x a day for 5 min. When it got hot this summer, the tree on the left (the one that’s in bad shape now) was looking like it needed more water.  Also, most of the rose bushes looked like they needed more water, so I set the timing to 2 x 10min. The rose bushes had improved. The tree seemed like it was getting better, but that was short lived and is now in the state you saw in the pictures.

I started reading on line – came up with all kinds of funguses that it could have caught.

A few other notes: I use Miracle Grow – one scoop every month or so per pot. Not so scientific, and now not so sure it helps.

As soon as I got your reply, I turned the timer to 2 x 5min a day and shut one emitter (in each tree) off entirely, the other emitter I closed down to a drip (when wide open they squirt 6 little streams out). Do I need to worry about under-watering?

Today I got home early, and took a drill to the bottoms of both pots, putting a ton of holes in the bottom, and all the way around the bottom vertical side edge, and put a few holes even further up.  Not an easy task – these things weigh a ton and I had to tip them and move them around. From this I learned that there are stones in the bottom of the pots – maybe a couple inches deep. I also learned that the dirt in the pots is dark black, and pretty wet from what came out on the drill; not sure but these pots may be full of plain potting soil.

So from what you said in the web site, do I need to dig the trees out of the pots and try to get the dirt out of the roots? Won’t that hurt them? I’m not even sure I will be able to do that. If so, from what your article says, I should get a bag of peat moss, and a bag of wood chips (like when they shred a tree on the side of the road?) and mix them up, then mix that in to be about 40-50% of the soil in the pot? If I am going to try this should I do It now? Or wait till winter? I am in NYC.

My gut tells me that in the spring I will be finding out how extensive the damage to the tree is; should I cut off all the branches without buds at that time?  I think a lot of it will probably live – it’s sending out new little branches with leaves on them in a bunch of spots now.

Oh – another question – why on the “healthy” tree have the leaves turned green?

Reply: The growing medium probably contains a large number of weed seeds so should be discarded and fresh potting mix used instead. As they are still in growth it’s best to wait until the leaves have dropped and they go dormant. What dirt can’t be removed by hand should be washed off so that you end up with completely bare roots.

The new growing medium of equal parts peat and chipped bark will require the addition of powdered dolomite (magnesium) limestone to neutralize the peat. Half an ounce mixed in with each gallon of peat will bring the pH up to neutral – they don’t need an acid soil. Garden World in Queens (www.igardenworld.com) sells bags of Schultz peat and potting bark. You could also try Plantworks on 800 611 2270. If you can’t get straight peat, any multi-purpose potting compost will do but avoid anything with Miracle Grow on the bag! Roadside tree shreddings should be avoided as they will need composting for a couple of years before they can be used.

For feeding, a few ounces of fish, blood and bonemeal mixed in with the growing medium will suffice, and then subsequently sprinkled on the surface once a year. Alternatively, a 12 or 24 month slow release fertilizer can be sprinkled on the surface next spring. Again, do not under any circumstances use Miracle Grow. The two contacts above can probably advise you on suitable slow release fertilizers.

When you repot, it’s not necessary to have any stones at the bottom of the pot; if you don’t have a free-draining growing medium a layer of stones or crocks will make no difference. It would also be helpful to mulch the surface – a sheet of plastic held down with a thin layer of stones will ensure moisture levels don’t fluctuate too much. In their present state the likelihood of under-watering is probably non-existent as the root-ball sounds as though it is completely saturated and your revised settings will be more than adequate. The existing pots can be re-used.

As to a fungal infection – this can be discounted as the damage stems from the roots being water-logged and fungi are only going to be interested in feeding on dead and decaying wood. Any dead roots should be pruned back to healthy tissue once all the potting soil has been washed off. They can be distinguished by a black surface colour.

Dead branches can be pruned off now. There will probably be some more die-back over winter but to be certain you’re not cutting into healthy wood, leave that until the plants have fully leafed out.

As to the change of colour, you probably have seed grown Acer palmatum atropurpureum. The intensity of colour and for how long it’s held varies from plant to plant and putting them in full sun won’t make a great deal of difference. If at any time in the future you want a Japanese maple that holds it’s colour all season, then go for a named cultivar such as Bloodgood or Fireglow. Alternatively, dwarf cultivars such as Shaina or Skeeter’s Broom would be suitable.

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