Right I planted my pea plants into the ground. They're climbing nicely. But how do I get maximum growth from them? Do I need to feed them?

There are two parts to the answer to this question. First, peas grow quickly and readily with little assistance. Being legumes, they are also nitrogen fixers capable of drawing nitrogen out of the atmosphere and into the soil. Any ocean-based foliar spray fertilizer, for example liquid seaweed, kelp, etc. readily available in the market, will provide vigorous growth. Second, peas are one of the miracle plants. The more you pick, the more they produce. Pick often and early.

As a last note, peas don't like hot weather. So shade them if necessary if you're in a hot climate.