Grow 507: Mulch off beds, clean garden, compost

Early Spring!

In the garden, cleanliness is not necessarily next to godliness


Dear Readers,

I'm continuing to work through an unusually high volume of mail. I've condensed my advice on the hottest topics to cover as many of your concerns as I can.

Short reports

Do I have to take the mulch off my beds?

No. At most of the U.S. public gardens I've polled, mulch is left on the beds year round. It's topped up whenever the gardener notices that it's decomposed to less than about an inch deep. Fall is high season for mulch renewal. It may be applied deeper then, since it will partially decompose and settle by spring.

It's an English convention to remove mulch from a bed in spring. The tradition might date back to the Roman occupation and the fact that far-north latitudes receive lower angle, weaker sun than Mediterranean climes. Bare soil, darker than most mulches, absorbs more heat and warms up more quickly than covered soil. Thus vegetable-planting can happen sooner. In the U.S. Midwest, we receive stronger sun than England does. Our soil temperatures jump rapidly in spring, no gardener-assist necessary.

I was told a healthy garden is a clean garden, so I rake everything out in spring.

The advice to keep a bed cleaner to keep it healthier is right on if you have experienced serious disease problems with specific plants, or are growing plants you know are disposed to certain life-threatening diseases. It can pay to remove all the debris that falls from such plants, not every plant, removing the affected material not just once a year but on a regular basis and disposing of it in a hot compost pile. This reduces the sources of infection. However, in an otherwise healthy garden, that protection's not needed. Plants and soil can benefit more from continual replenishment of organic matter through decomposing plant matter.

Although fallen debris can harbor trouble-maker insects and diseases, it is also home to beneficial insects, helpful fungi and bacteria -- organisms which far outnumber their pesty counterparts. Leaving healthy debris in place helps maintain a balanced garden ecosystem. Pests will be preyed upon by their natural enemies and we will have less work to do since we won't have to get involved in every battle.

Can I make the soil in my perennial garden better without digging out all the plants that are already there?

Certainly! Each year, add two or three extra inches of compost or organic matter between plants, keep it moist and let Mother Nature's tillers go to work for you. This technique doesn't pay off as quickly as removing the perennials or bulbs and then digging to loosen the soil, but it works!

If you add an extra-deep layer of compost or shredded leaves while the ground is still cold, you can cover right over perennials, which will usually emerge without trouble. My soil-improvement routine is to top-dress beds with compost in fall, since the window of cold-weather opportunity is larger in fall than in spring. This spring, the window may be especially small, since late springs come on fast and progress very rapidly.

You can also improve the soil with plants in place by drilling holes throughout the area and filling them with compost. In relatively loose soil, a bulb auger does the trick but where the soil is very heavy and packed down, I rent a power post hole digger.

Call Miss Dig before you drill (800-482-7171) so that major utilities can be marked before you start drilling. Keep in mind that utility companies can only locate your primary connections to electric, gas, phone and cable TV, not all the secondary connections and other items that may be buried on your property. Locate sprinkler lines first, if you have a buried irrigation system, avoid invisible dog fences, and avoid the power or gas lines to outdoor security lights.

Can I add soil over tree roots to make a garden?

Yes. You can make a new garden or improve an old one by raising a bed under a tree. Don't use soil, though. Use compost. This mimics natural soil-building in a forest, where thick layers of fallen leaves decompose and build new topsoil every year.

Always keep the trunks of woody plants clear of whatever you use to raise the grade, however. If you walk in the woods you'll see how normal leaf fall and wind patterns keep debris from accumulating directly against tree trunks. Mulch and other organic matter stacked against a trunk can kill even a large tree through butt rot.


Green thumbs up

to steady cold, for bulbs' sake. Bulb plants may be better off this year than when winter warm-ups cause their foliage to emerge early. Although precocity doesn't kill the bulb it can freeze leaf tips, making them less attractive, more susceptible to leaf spot fungus, and less energizing to the flower.


Green thumbs down

to breaking the icicles off shrubs. Certainly you're anxious to remove the last bits of winter but you damage the wood when you beat and snap off ice. Support the frozen limbs with props instead, and let everything melt gradually while you look at ways you can prevent that freezing drip next year. 


Originally published 3/15/03