Monday, June 18, 2018
Home and Garden

Dr. Hort: Inorganic mulches, rust fungus, pruning crape myrtles

Use an inorganic liner

Q: When I purchased my house, it had lava rock in the garden, so we have continued the use of it. I've just weeded the side of my house and now want to put lava rock down. Should I put some newspaper down first? I think I have read you can use that or plastic. Thanks for your help.

Mary Telford

A: When using inorganic mulches like your lava rock or river rock, granite chips and rubber, it is a good idea to also put an inorganic liner under it. If you want to remove the mulch at some point down the road, it is easy to pick up and hasn't worked itself into the soil. Products sold as weed barrier would work. Better yet is polypropylene weed mat, but it is perhaps a bit harder to find.

Pruning a crape myrtle

Q: I live in Palm Harbor. I have a crape myrtle tree, 20 to 25 feet high and about 18 feet across. When should I trim it back?

I read February, so I did so in the past, but by doing it in February my tree was the last to bloom in the area, losing one month of flower production. Last year, I trimmed it back in December but I thought it was too soon and I cannot find any literature suggesting I should do it that early.

Tom Kulaga, Palm Harbor

A: The time to prune deciduous trees like your crape, Lagerstroemia indica, is after the leaves fall. With the tree leafless, you can easily identify criss-crossing branches that should be removed. Any other pruning to control growth should also be done at this time. So the best time to prune is not necessarily a particular month, but as soon as leaf drop is complete.

Fungi on frangipani

Q: I'm seeing orange musty film on the bottom side of the leaves on my plumerias. What's the best treatment to get rid of this? Thanks for your help.

Jean Pelak

A: What you're seeing on your Plumeria spp. in grand detail are the fruiting bodies of a rust fungus. It is through these structures that spores are spread to infect yet another plant. If you have an infected frangipani, the top side of leaves turn various shades of yellow, tan and brown, and the bottoms full of bright yellow to orange spore bodies before they drop.

Rake up the leaves as they fall and discard until the plants are bare, as they are deciduous. Next season you can let nature take its course and implement the above strategy or you can spray with a protectant fungicide, such as 1 tablespoon neem oil plus 1 tablespoon baking soda with a gallon of water, at the first sign of a spot. Continue applying weekly throughout the season to keep the leaves clean of the fungus. The rust fungus won't kill your plants, so "to spray or not to spray," that is your option!