Critical Points of Influence: Vegetative Growth

In this final post of our four-part series on John Kempf’s idea of “Critical Points of Influence”, we’ll be discussing Vegetative Growth.

If you missed the previous three posts, you can find them here:

• Introduction
• Bud Initiation and Bloom
• Cell Division, Fruit Fill, and Ripening

Vegetative Growth

Fast vegetative growth is very easy to achieve: dump on nitrate nitrogen and watch the plant take off. But not all vegetative growth is created equal: plants grown in such a way will have widely-spaced internodes, meaning they won’t have as much reproductive potential as plants with tightly-spaced internodes.

But by having high levels of a different nutrient–calcium–it’s possible to achieve strong vegetative growth that has tight internode spacing, giving the plant the best possibility to grow a bounteous crop.

What can we influence at this point?

Rapid vegetative growth while maintaining tight internode spacing

• Tight internodes give more opportunity for reproductive buds in the future

High-carbon wood on perennial crops

• This will give higher future reproductive potential

Disease and Insect Resistance

• We’d like to achieve lots of vegetative growth without having nitrates present
• Nitrates are like blaring neon signs for insects

How does calcium drive healthy vegetative growth?

There are 4 nutrients which drive strong vegetative growth: nitrogen (only in its nitrate form), potassium, chloride, and calcium. Of these, the first three (NO3, K, Cl) have a synergistic relationship with the hormone auxin. High levels of these three elements will produce auxin dominance in a plant and rapid levels of growth.

However, calcium has a synergistic relationship with cytokinin. You’ll recall that cytokinin is the reproductive hormone–it’s produced in growing root tips and triggers reproduction. So calcium is unique in that it has a foot in each realm–vegetative and reproductive.

When you use calcium instead of nitrogen to drive vegetative growth, you can achieve the same vigorous shoot growth, but with much tighter internode spacing, giving the plant a higher reproductive ability.

Boron is another important nutrient for vegetative growth, since it synergizes with calcium.

A note on bulbs

For crops like onions and garlic, the development of the bulb is essentially a vegetative process. So the largest and firmest bulb will grown when the plant has good vegetative energy–large, wide leaves, good cell division, and continuous vegetative growth in the bulb right up until the last week or two before harvest.

Conclusion

This introduction to Critical Points of Influence has necessarily been very high-level. Each crop plant has a different number and type of Critical Points of Influence, and they come in different orders and different times of the season. It’s important for you as a grower to know your crop, and when the Critical Points occur.

But by focussing on taking action during these narrow-yet-important windows, you can get the most out of your nutrient applications, and ensure that your management actions will actually have an effect on the thing that matters most: your bottom line.

Further Reading

John Kempf’s ideas about Critical Points of Influence were primarily influenced by Jerry Stoller. Stoller Enterprises has published a 20-page “Crop Health Guide” with more information about auxin, cytokinin, plant hormonal shifts, and the nutrients needed at various points in time. You can find their guide and its bibliography here.