Question
Hi Greg,

Hope you can help with our cactus problem.

We have a Cereus (Peruvianus I think) that has 3 independent columns. We shipped it recently from USA to UK and it turned up looking quite well although the top of one of the stems had been been seperated at the join of a new growth.

When we shipped it we had to remove all soil from the roots due to import requirements. The stems were wrapped in thick packing paper which was backed with some kind of material/fabric and packed in strong boxes so they were fairly well insulated and protected from physical impact.

I repotted them in new cactus compost after leaving them a couple of days after unpacking in a coolish dry room.

Since then the tops of the cactus have started to go soft and turn black. Two of the bottom stem segments also appear to have turned a lighter green.

The cactus stems are from 2.5 to 6 feet tall. The cactus was indoors in our apartment in NJ which was well lit with sunlight.

I've read some posts regarding frost damage. I don't know if it is cold temperatures or frost/ice that causes the damage? The cactus may have experienced cold temperatures but were wrapped up so wouldn't have seen frost.

And other posts say cactus going black from the top may be root damage.

So should I chop some off the top where it's black or off the bottom if it's a root problem? Or both? Or something else?

I bought a high pressure sodium lamp as I thought the problem might have been due to lack of light over the 3 weeks it was in transit and we have had very little natural sun due to lots of gloomy days here in the UK. Am I in danger of giving it sunburn? What are the symptoms?

Can you help please?

Thanks in advance,

Regards,

Jarrod

Answer
Dear Jarrod,

Typically, black tips mean frost damage, but since they are the "newest" parts of the plant, they can also be damaged by cold temperatures. Something else, if this was strictly an indoor plant, it will be particularly sensitive to cold and bright sunlight.

The light green area may be the part of the plant that was below the soil level. If you have already repotted the plant, I would wait until the plant has had a chance to acclimate before cutting off the black parts.

However, if you actually have an Euphorbia Ingens (which looks almost identical to Cereus Peruvianus), then I would cut the blackened areas off. The difference is that a Euphorbia has a fluid in it called latex that will spread the rot throughout the plant. Check out both of these websites to see the difference in the plants.

http://yann.cochard.free.fr/images/14/1467.jpg

http://www.ogrod.uj.edu.pl/_img/kaktusiarnia/Cereus%20peruvianus%20kopia1185002....


Hope this helps,

Sincerely,

Greg