"soft spring" is correct and usable in written English.
It can be used to describe a season, e.g. "The soft spring air brought a welcome feeling of renewal."
The cubic hard spring and cubic soft spring are characterized by the non-dimensional coefficient σ2s0ε where σs0 is the r.m.s.
— May 10 , 1982From "A Soft Spring Night in Shillington," a memoir Two sensations stood out as peculiarly blissful in my childhood, before I discovered (at the same time as leaving Shillington) masturbation.
The probability density function of spring displacement is determined analytically by means of the Fokker-Planck equation and both r.m.s. and mean peak values of spring displacement and mass acceleration are presented for three types of spring non-linearity: (a) cubic hard spring, (b) cubic soft spring, (c) tangent spring.
— May 10 , 1982________ From "A Soft Spring Night in Shillington," a memoir Two sensations stood out as peculiarly blissful in my childhood, before I discovered (at the same time as leaving Shillington) masturbation.
MAYBE it was just the warm weather, but consumers went on a shopping spree last month at America's malls and stores, giving major retailers a healthy sales gain after a soft spring.
We skied hard all morning on soft spring snow.
