Coslett said Palmstead has decided not to import high risk specimens and will now seek to increase production of plants such as rosemary and lavender, and find alternatives to specimens such as olives.
Coslett added: "We imported rosemary and lavender at those times of the year when our production was on the low side. We will increase our production to fill that sort of gap.
"We have to act responsibly as a grower, importer and supplier."
Palmstead is also starting to grow more phormium again.
He said he will stop importing any olives and have to hope designers understand when current quarantined stocks are sold they can't get any more in.
He suggested willowleaf pear, cornus, arbutus or pines as alternatives.
Coslett said biosecurity in some of the Mediterranean countries hit by Xylella is "tricky" and "we're not able to rely on these nation states' own plant health systems - we can't rely on them to protect the UK".
He said Defra don't want to "rock the Brexit boat" too much though believes Defra secretary of state Michael Gove wants more restrictions in place. Some continental growers say EU rules are too draconian and are driven by the French to protect their wine market.
There are no controls and no way of stopping Xylella migrating through southern Europe. The EC extended the 300-plant host list this month.