The Horticultural Trades Association has warned that up to £200 million worth of plants could end up being thrown away because they cannot be sold due to emergency restrictions.
Graham Loines, who keeps the family-run Wenlock Nurseries in Swindon, near Dudley, said he was seriously worried about whether he would be able to continue in business.
He said most of his business was wholesale to garden centres, which had been forced to close.
Mr Loines said poor weather had already forced him to bin many of his early-season plants such as primroses.
"We have now got the perishable plants, the bedding plants, coming through, and if the garden centres are not back open soon we could end up throwing them all away," he said.
"Our main season isn't until May, about the first week of May our sales are really strong.
"If the restrictions aren't lifted by then I am worried we will go out of business."
Mr Loines said the nursery, which has been in the family for more than 60 years, was supplementing its income at the moment by selling vegetables.
David Cank, who keeps Severndale Nurseries, near Shrewsbury, expressed similar concerns.
"A lot is going to depend on how long this lockdown goes on for," he said.
"If we get to the end of May or June, our main months, and if we are not open, or our customers. the garden centres are not open, that will be dramatic.
"We have been in the business for about 60 years, and we have never had anything like this to face in the past."
Rachel Maiden, general manager at Ashwood Nurseries at Kingswinford, near Dudley, said it was too early to say what the long-term effects would be, but added that it was a worrying time.
The award-winning centre is closed to the public, but is still supplying plants through it website.
Mrs Maiden said the effects would probably depend on how long the lockdown period continued for.
"We have got short-term crops, mainly bedding plants, which we need to get on our website," she said.
"I dread to think how many of these will end up in the skip if this goes on."
David J C Austin, managing director of David Austin Roses in Albrighton, said it was a difficult time.
"As with many horticultural businesses we have gone from welcoming visitors and preparing for our busiest time of year to closing our gardens and operating on a skeleton staff in a matter of days," he said.
"It is anything but business as normal. First and foremost we are doing everything we can to protect the health and safety of our staff and wider community. However, we are also doing the best we can to ensure the welfare of our roses.
"We are busy safeguarding our current stock and planting new roses to make sure we still have roses to provide to our customers once this has passed. If anything positive is to come from this outbreak I hope that people re-ignite or find a new passion for gardening."
The Horticultural Trades Association (HTA) is calling for Government support of the ornamental crop sector, which grows bulbs, bedding plants, cut flowers and pot plants for garden centres, supermarkets, florists and DIY stores.
The call has been backed by TV gardener Alan Titchmarsh, who warned of "irreparable damage" to gardens and open spaces if the sector is not supported.
The HTA says around 650 businesses across the UK produce ornamental crops, contributing £1.4 billion to the economy each year and employing more than 15,000 people directly and almost 30,000 indirectly.
Sales have dwindled since the Mother's Day weekend, when demand would be normally high but people were already beginning to self-isolate, the trade body said.
The value of lost plant sales in the UK will be £687 million by the end of June, the HTA suggests.
Mr Titchmarsh said: "Hundreds of nursery owners and growers are facing huge losses of plants and revenue simply because the stock they have spent many months nurturing for the spring market – their peak season – will have to be destroyed since garden centres and other outlets are closed for business.
"This means not only a loss of billions of pounds to the UK economy and of thousands of jobs but, more than this, it will decimate an industry that will be unable to recover for the foreseeable future.
"I urge the Government to put in place a rescue package which will enable British horticulture to survive.
"Without it, our gardens and open spaces - a vital source of solace and nutrition to those at home - will suffer irreparable damage."
HTA chairman James Barnes warned that growers are facing stock losses on an ever-rising scale as each day passes.
"We are calling for the Government to work with the HTA, as the industry's representative body, to come up with a financial support scheme to help those businesses which have had to scrap perishable stock and are facing a huge financial crisis."