WASHINGTON (REUTERS) - First Lady Michelle Obama shared what has become a rite of spring in Washington with a small group of fifth-grade students on Thursday, planting vegetables in the White House garden.

On a day that began with record-cold temperatures that have pushed back the blooming season for the city's famous cherry trees, Mrs Obama welcomed about 30 students to help her plant the garden, a project she has championed as a model for children and their parents to emulate as a way to reduce childhood obesity.

"Where are your jackets? I'm going to be the mother," Mrs Obama joked with the group of earnest, polite kids, most wearing t-shirts bearing the names of their schools in Florida, Massachusetts, Tennessee and Vermont.

Mrs Obama has helped push for changes in school lunch rules to require more vegetables and fruit. The schools were chosen because they have implemented the new rules in creative ways and started their own gardens.

Harvard-educated Obama, who was more popular in polls during the 2012 election campaign than any of the candidates, started the garden on the White House south lawn in 2009, the first time vegetables had been grown there since Eleanor Roosevelt's "victory garden" during World War Two.

Mrs Obama, sporting sneakers without socks, put aside a pair of lime green gardening gloves as she crouched between two raised garden boxes, carefully placing tiny wheat kernels into freshly turned soil.

From Somerville, Massachusetts, 11-year-old Ariana Docanto chatted with Mrs Obama as she helped plant the wheat, which the White House hopes to harvest and use for bread and risotto.

Docanto described the experience in a single word:"Amazing!"