Many non-store garden retailers use alternative postal providers but those still with Royal Mail are hoping for a swift resolution so as to avoid destroying consumer confidence in the vital run up to Christmas.
BRC head of non-store retailing Sharon Hardiman said: "Online and mail-order sales grew more rapidly than last month thanks to a minor revival in some customers' moods, but September growth was still the third-weakest of the year. How far this builds in the critical pre-Christmas months may depend on the postal strikes. Online's slice of overall Christmas spending hinges heavily on customers being sure retailers can get the goods to them. Online shopping is a big source of growth for Royal Mail. We all need common sense to prevail quickly."
Online gardening retailer Gardening Direct still uses Royal Mail for all its deliveries.
Chief executive Steven Cook said: "Although the effects of the strike on gardening products is fortunately limited at this time of year, there is no doubt that the longer the strike continues the greater the effect it will have on consumer confidence in the reliability of the Royal Mail. Like many others in this position we are investigating ways of mitigating the long-term effects on our business."
In order to minimise the impact of the industrial action, the HTA has taken steps to protect members.
It said all National Garden Gift Voucher (NGGV) orders placed between now and the end of December would be sent using the Parcelforce 24 courier service to maintain a reliable next-day delivery service. Despite this, the HTA urged members to stock up early to maintain NGGV stocks and to order cards and envelopes at the same time.
It also asked members to review how they submit claims during the disruption, encouraging them to use a courier service or to avoid using Royal Mail during or just before strike days.
The HTA said it would process claims as quickly as possible and would dispatch payment in advance of strike action wherever possible.
The arrangements are set to be reviewed in the new year.