Growing Concerns 403: Improve poor soil, weed by the moon, leaf mulch, slugs

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Soil moisture more important than fertilizer

Dear Janet,

I built significant gardens in my back yard with new top soil. Thinking that the soil must be good, as I paid a lot of money for it, I did little to fertilize. All my expensive plantings did not prosper. I have been fertilizing with Miracle Gro, peat moss and grinding up leaves and spading them under, with marginal results.

I've read articles about plants needing acid soil. Last season I sprayed with Miracid and got much better results.

Is there a regimen I can follow to turn my soil more acidic?

C.B., on the Internet

Dear C.B.,

You're barking up the wrong tree. Some plant species prefer acid soil -- low pH -- but most landscape plants grow quite well in any loose, well-drained soil that is "circumneutral" -- neutral or within a point either way of neutral on that pH scale. Great Lakes soils rarely miss that mark, even when stripped from one spot and moved to another.

Topsoil, by the way, is not priced for fertility but for the cost of moving it around.

When it comes to fertilizer, plants given the right amount of sun and water grow without it. Well-lit, well-watered plants would have grown passably well without fertilizing.

I suspect your problems are related to two conditions which are far more universal than pH in their effect on plants. How are the sunlight and water in your garden?

Sun is a plant's sole energy source. Plants use solar energy to turn air and water into carbohydrates -- sugars and starches made from carbon, hydrogen and oxygen molecules. Those fuel all other life processes in the plant. Fertilizer is like vitamins, not food, and cannot compensate a plant for too little energy.

Check your garden for hours of sun during the growing season, then check your plants in a garden encyclopedia to see if they are getting the light they need. Full sun plants need six or more hours of shadowless sunlight every day. Half sun and half shade species must have four to six hours of sun. Shade plants require at least two hours of sun each day. Move any that aren't getting sufficient light.

Water is probably another key to this puzzle. Across-the-board poor growth, pale foliage and root trouble often stem from too little or too much water.

Given too little water, plants can't fill up their cells or get hydrogen to make carbohydrates.

We had copious rain last year, so much more than usual that many plants competing with trees for their water grew the best their gardeners had ever seen. Are your beds under or near trees? Perhaps it wasn't fertilizer but rain that made the difference last year.

If water-guzzling trees aren't the problem, what about slow drainage? When there's too much water, all the air is pushed out of the soil. This kills roots, since they need atmospheric oxygen to live. Once roots die, the foliage receives less water, wilts and starves as if in a drought.

Drainage is not puddles on the surface in this case but excess water <i>in the soil</i>, in spaces where air should be. Excess water should drop quickly out of the top eighteen inches of soil or roots will die.

Loose soil piled on top of hard-packed earth tends to drain poorly. Water moves quickly through the loose soil but puddles above the denser layer. The sogginess of this "perched water table" may be invisible to us but is devastating to plants if it occurs within that eighteen inch root zone.

Do a drainage test to see how long it takes excess water to fall out of your soil. Dig a hole eighteen inches deep and fill it with water. Let that drain and then fill it again. Time the second draining. If all the water is not gone from that hole within a day, install a drain tile to remove it more quickly.

As for fertilizer, one in liquid form may have dramatic effect on plants which have lost roots in dry or overly wet soil. Products such as Miracid sprayed on the foliage can bypass a damaged root system, go directly into the leaves and may cause them to green up immediately. The plant can look better even though underlying problems still exist.


Timely Tip

Use the new moon to advantage. Moon-phase gardening lore tells us that the very best time to weed or destroy pests in a garden is during those days on either side of the new moon -- that's today and tomorrow. If you had a weedy area last year, rest assured those weeds are there still. Why not tackle them now?



Green thumbs up: to leaving fallen leaves on most beds, even several inches deep. Rake lightly to break up matted layers but don't remove them. Leaves not only suppress weed seedlings but will be broken down into natural fertilizer by worms and microbes as the soil warms.


Green thumbs down: to slugs, now emerging. In beds that had significant slug problems, do remove all leaf litter now. Set out slug poison or traps for several weeks. With little else to eat and no leaf litter to hide in, slugs take baits or fall for traps and you're rid of them before they do much damage.


First published 3/24/01













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