Gerard Lordahl on Plants, Inside and Out

Wednesday, November 28, 2012

Gerard Lordahl, Greening Director of GrowNYC, talks about how to care for your Christmas cacti and Christmas trees. He’ll also address recovering your garden after Sandy—replacing soil that was washed away, whether to get soil tested for contaminants, as well as how to deal with fallen trees and replacing trees.


Gerard Lordahl

Comments [16]

regarding the Avocado dying it could be wrong soil. Peat moss based commercial soil does not allow enough oxygen reach the roots. I would mix soil, perlite, fine bark in equal parts. I do not think low humidity would kill an avocado seedling so quickly (don't they grow Avocados in California where relative humidity levels are low?). Wrong soil medium will kill a seedling quickly.

Also roots that started in a glass of water are structurally different than roots that started in soil.

You could try to transition the seedling from the glass into quality sphagnum moss

Nov. 28 2012 12:41 PM
Leah from upstate manhattan

shout out to Julie about the vines on the Sawmill Pkway! By August, those trees look like some monstrous green bio-imitation of the Thanksgiving Parade balloons.

Nov. 28 2012 12:39 PM
Franco from Sag Harbor, NY

In Sag Harbor the yard was flooded and now the ivy plants are shedding all their leaves. Is it because of the salt water? Will the damage be permanent?

Nov. 28 2012 12:38 PM
Leah from upstate manhattan


Some large trees that came down in Central Park revealed rotted interiors. How come they were rotten? We wonder about pruning practices in NYC parks -- the way they're cut seems to invite moisture and disease.

I don't know if the guest is the right person to ask but perhaps he knows...

I hope this is not a political question!

Nov. 28 2012 12:36 PM
Julie from NYC & Vermont

There are HUGE vines that come out of the ground and are strangling the trees along the Saw Mill Parkway. I've seen these vines also in our forest in Vermont. What is this? Where does it come from? How does it climb the trees? Why doesn't Westchester County cut the vines? They are easy to cut in half with a good pair of clippers and are filled with water it seems.....

Nov. 28 2012 12:36 PM

The Opuntia the guest referred to is Opuntia humifusa. Other Opuntias are not hardy in NY/NJ. I saw Opuntia humifusa growing on a stone wall near the GW bridge on the NJ side.

Opuntia ficus-indica is a species that provides edible fruit (prickly pears) and pads (nopales).

Opuntias are really easy to propagate, just get a pad and stick it in soil it will root.

Opuntia humifusa in the winter will shrink and look like a prune, but it will plump in the spring. It needs reg water in the summer, it is not a desert cactus. Not all Opuntias are the same.

Nov. 28 2012 12:33 PM
Rori from LI

I've heard that rather than sending out the soil for testing, it is possible to test for salt contamination by simply seeing if a pea or bean seed will grow. True?

Nov. 28 2012 12:30 PM
Leah from upstate manhattan

Does the guest know what happens to the tremendous amount of biomass that was felled in the storm? Who gets to keep it? Thinking of all the trees and branches in public parks -- is it all composted or is some of it sold? Doesn't it belong to the people of NYC?

Nov. 28 2012 12:27 PM

Why can't I get a plant from an avocado seed to live? They are so easy to get rooting in the little glass of water with the toothpicks. But once I get it into a pot, it lasts a few more weeks and perishes.
I live in Texas.

Nov. 28 2012 12:27 PM
Tina from Long Beach

Our organic vegetable garden on Long Island took a beating from Sandy floodwaters: ocean, bay, not to mention sewerage overflow seeped in. Now we are worried about salt, e-coli, etc. On the other hand, it's mostly just water, right? Must we change all the soil for spring planting? Any advice?

Nov. 28 2012 12:24 PM
Meg from NJ

As you just described for geraniums, can you shake off the dirt and put Begonias upside-down in a a cool dark place?

This could save me on the cost of replanting annuals!

Nov. 28 2012 12:24 PM
LongIsland Grower

How often should I water my potted fig trees (each which are around 7ft tall) that I store in an unheated but sunny room (that remains > freezing) over the winter?

Thank you

Nov. 28 2012 12:22 PM
Anne from Bronx

My garden has a thick layer of uncrushed fallen leaves over it. Can I use the leaves as mulch?

Nov. 28 2012 12:21 PM
Maude from Park Slope

I have large wooden pots out on a roof, and one of the pots got grubs in it--not sure what kind of grubs, maybe japanese beetles. They completely killed the flowers in the pot--
do I need to take all the dirt out of the pot, or will frost kill them? its a huge pot and I'd really hate to have to throw the whole thing out. Also, will they migrate to other pots? Aack. Any advice? thanks!!

Nov. 28 2012 12:21 PM
Matthew from New Rochelle

Two questions for your guest please :-)

1) I have a 12 ft Hellinski Cypress that I never got around to's in a 50" plastic pot. Can I plant it now or is it too late and should I leave it in the pot for the winter? It has excellent drainage.

2) What is the best treatment for indoor pests like spider mites, mealy, and scale. I've used hot pepper wax liquid, target oil (mess!), Safari, and my favorite...Talstar! That's for when they are really getting on my nerves. Thanks to the old crow who gave me a bottle from her antiquated stock!


Nov. 28 2012 12:13 PM
Sher from Lower Manhattan

Just brought my geraniums in from the fire escape to avoid frost. I know they will grow "leggy" on interior window sill in the weak light, so should cut them back, BUT, to root the cuttings for next spring, should I put them in Water or Dirt?

Nov. 28 2012 12:12 PM

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