He said he is offered more and more cheaper trees but wants to concentrate on quality, with 70 per cent Irish and the rest from Scotland and the continent.
Mitchell said educating staff to look after trees meant "minimal" returns during last year's warm December.
He said sales were over 85 per cent Nordmanns and overal Christmas tree sales had risen in 2015.
Mitchell said on plant supply: "We're almost at the point where we couldn't get much more from the UK, but "short-term volatility" with the euro would not stop imports of plants he couldn't source here.
Marketing and communications director Justine Noades said Wyevale has reduced its Christmas range since 2015 to help marketing and make sure more of the range is in more of Wyevale's 152 centres.
She said Brexit and the subsequent weakening of sterling against the dollar would not make a difference to wholesale and retail prices at Wyevale until 2017. "We bought in February. It's going to be next year and how we hedge the currency."
Christmas buyer Laura Comfort said 60 per cent of the "consolidated" range is exclusive to Wyevale, sourced from China through mood boards sent over to create a UK-focussed offer, rather than the US products habitually produced for Christmas in the Far East. She said 90 per cent of product is new.
She said against a "backdrop of a difficult Christmas" influenced by Black Friday and cyber Monday in November, Wyevale were "pleased" with sales in December 2015.
Theme is a traditional red 'joy of Christmas'.
Burgon & Ball's RHS range is a central Christmas gift idea.
Food such as sparkly meringues has been added as Christmas gift offer, said food buyer Suzi Bailey.
HW published Wyevale's 2015 sales figures last week. The chain called the year "challenging".
See more in next issue of Horticulture Week.