I have some kale that I planted in a raised bed. It is growing well and I take out leaves as and when I need it. Of course, it keeps growing new leaves. My question is at what point will the kale stop producing (or die)? The motivation for my question is to start planning for the next set of plants to put in place of the kale when they eventually stop producing.
Depending on the zone you are raising Kale the main sign that that Kale plant will stop producing is when it flowers/produces seed. Bolts...keep those flowers off that plant, use higher nitrogen when fertilizing and it should last most of the season. It is an annual normally. An annual has only ONE purpose in life and that is to make seeds, babies. You cut those babies/flowers/reproductive structures OFF and that annual gets bigger, healthier and REALLY starts producing. Now an annual where you only want vegetative growth you make dang sure you NEVER allow any energy to go into seed making. You do that by using NPK ratios so that the N is higher in number than the phosphorus and potassium. You cut off chop off any reproductive growth that starts. When the daylight hours shorten you'll not be able to keep up as that is another trigger telling that plant time is short and you need to make seed! I am not advocating LOTS OF FERTILIZER. It is simply the PERCENTAGE between the three vital chemicals plants need to have in a domestic garden. Higher the number on N, you get vegetative growth...leaves. Lower than number below the P and the K and you'll get more reproductive growth. Once that plant sets seed...hey its life is fullfilled and will start dying.
If a gardener wants more of a vegey, definitely what you intuit is to start fresh crops every 2 weeks apart...hey, what do you use your kale FOR? I love Kale.
I had kale survive on my allotment over winter to April this year ( middle of the UK, ~200m high ). The hardiness depends a lot on your variety, but as long as you keep pinching off the flowers it'll last for a long time. At some point the taste will become unpleasant as it puts all its energy into seed production. Its probably better for you to decide when you need to plant the next crop than to guess the lifetime of Kale.