Withdrawal when taking the lawn off pesticides...In the above picture, 3 year old Sean planted the bean in a small cup as a preschool project. As you can see, the plant has successfully created a new bean pod! But how long can this success last? It's pretty obvious in this picture, that sustaining a healthy plant in such a small piece of soil will eventually take more than just water. All that plant growth requires nutrients to come from somewhere...and (initially), the plant finds all it needs in that little cupfull of dirt...but as the plant grows, the nutrients are depleted. When the nutrients are gone, the plant will suffer.
Thinking about the soil that gives our plant nutrients is a key concept in organic gardening. To be organic, the soil must stay healthy to give the plant a good environment. We don't just focus on the plant by dumping extra water and fertilizer on the soil...we take care of the soil, so the plant can get whatever it needs. This is a key organic mindset: take care of the soil.
Just like Sean's cupfull of dirt, the soil under our lawn is also responsible to feed and water the plants above. Sean's little bean plant needs to be watered, every day, to keep the plant alive. And very soon, the plant will have depleted the nutrients in the soil...in fact, it's started already (notice the slight yellowing of the leaves in the middle of the picture?).
The typical lawn has a layer of topsoil where most of the lawn roots feed. Under this topsoil layer, is the subsoil...this subsoil layer can have a mixture of sources: the deep dirt from the excavation of the house's foundation, and perhaps some construction debris mixed in. The subsoil does not contain alot of useful nutrients for a lawn...the topsoil has to provide everything. If the topsoil layer is thin, then "Sean's Bean Effect" kicks in. The lawn will need more watering, and extra nutrients, in order to stay healthy.
Can you imagine what the roots of Sean's Bean look like in that tiny cup? They are most likely a tangled mess, as they search out and occupy every last spoonful of useful dirt.
Our lawn can have the same problem when the topsoil layer is thin...all the roots live in a narrow band close to the surface. This type of lawn will need water often...it will need fertilizer to replace what the grass takes out...and it also needs protection from any number of lawn pests.
One such pest is the Japanese Beetle (<-- click on word to see description). The adults lay their eggs on the lawn, and the hatching grubs of this beetle live under the grass, eating the grass roots that are growing in the topsoil.
A few grubs in the soil will not do any noticeable damage...the grass can recover. And nature has a way of keeping the grub population down in a healthy soil. One significant way is the Nematode (<-- click). These microscopic worms live and multiply inside the grubs (ick!) until the grub dies...then the nematodes go after other grubs. This is part of nature's balance, and it all depends on the soil being healthy (organic) to support all these creatures.
Taking the lawn off pesticides
If pesticides were previously used, the grubs were initially killed off by the poison. And other insects (both "harmful" and "beneficial") would have been killed off too. It is very possible that beneficial nematodes are absent from the lawn when the pesticide use stops. And being microscopic, the nematodes do not repopulate the lawn quickly.
By contrast, when the pesticide is later stopped, the adult beetles fly everywhere, and lay their eggs all over the lawn. Then the grubs eat the grass roots without any natural predators to keep them in check. More than 50% of a lawn can be lost in one season when this happens. We took our lawn off of pesticides when we moved into our house 3 years ago. The Japanese Beetle laid their eggs on the turf, and wiped out the lawn at the end of the first summer.
Rehab for our lawn
To recover, we top dressed with 2" of triple mix to reduce the "Sean's Bean Effect". Next we added nematodes using a garden sprayer. Then we re-seeded with regular grass and white clover. The clover roots dig down into our clay subsoil, and fix nitrogen from the air in their roots. Then the grass takes the nitrogen and grows stronger. We don't fertilize or water our lawn anymore...the soil takes care of the grass and clover by itself.
Nematodes are available at many garden centers if you want to check them out. We only did this the first year, and now the occasional grub isn't a problem.
If we want to grow something and avoid "Sean's Bean Effect", we will need to focus on what's underneath. Whether it is topsoil for a lawn, a cup for a bean, or even a planet for you and me....it's what's underneath that needs to be kept healthy and in balance if it is to sustain the life on top.