Growing Concerns 588: Loosen garden soil, indoor fertilizing

In this issue:

Fall is for loosening the soil
Cutting back perennials
Fertilizing indoor plants during winter
Mildew is reason to dump a phlox
Soil test and drainage

Loosen the soil now for better lawns and gardens by spring


Dear Janet & Steven,

I try to keep from stomping around in my garden, but sometimes I have no choice. As hard as I have tried to prevent it, the soil seems very compacted. 

Is it better to go after it with a fork and loosen the soil NOW, or in the spring? (This assumes I can manage to miss the irrigation tubing and not sabotage my marriage!) - C. -

Dear C.,

We aerate compacted lawns and gardens in fall. That way infiltration rate, moisture level and oxygen content are better below ground during both important root-growing seasons, fall and early spring.

Garden fork, indispensable soil improvement tool

Use your spade-sized garden fork, just go easy. Irrigation tubing is usually deeper than your fork's tines need to go, since compaction from occasional foot traffic extends just one to three inches below the surface. Work carefully, and even if some sprinkler lines are shallow enough to be in your work zone you'll feel them and be able to pull back before puncturing anything.

Irrigation lines might be acceptable collateral damage

If you do suspect a puncture, dig there and feel the pipe for "wounds." Tie a bright colored cord to any nicked or pierced pipe, leaving the end of the cord visible above ground to mark where repairs are needed. Sprinkler lines are simple to patch, a small price to pay to amend soil too dense for good root growth.

Don't turn the soil. Insert the tines, then lean back so the ground "pops." You can aerate right through a mulch, or add new mulch as you go. Walk backward as you pop the soil so you never stand on any space you've already loosened. You'll work wonders by forking that top layer. Moisture and soil animals will move into the air spaces you created, extending them and distributing soil-enriching humus throughout the bed over winter.


Cutting back perennials

We have balloon flower (Platycodon), bellflower (Campanula) and Lamium maculatum 'Orchid Frost' perennials. Do any of these need to be cut back in the fall? - R. -

Dear R.,

No perennial needs to be cut back in fall. They manage in the wild without us and, given good growing conditions, return each spring regardless of our treatment.

However, you can cut back all of yours if you like, to tidy up or to clear the deck and simplify fall weeding.

Another reason to cut perennials back would be to remove foliage that hosted an insect or had leaf disease. Removing that debris might decrease the plant's chances of developing that same problem next year.

We often leave Lamium alone, so long as it was healthy enough to avoid the fungus called "melting out," a common midsummer problem for this species. Left in place, its semi-evergreen foliage can be a plus in the late fall and early spring garden.

Short reports

Stop or reduce fertilizer to indoor plants.

I.S. wonders how fertilizing and watering should change for a tender hibiscus now that it's indoors to overwinter as a houseplant.

Fertilizer does not cause growth, it simply supports a growing plant the way vitamins benefit developing children. So fertilize only when a plant is growing. 

In winter, most plants don't grow. They sit and wait. Hibiscus is typical. On a windowsill, it grows very slowly if at all between October and March. So all it needs is water, applied only when it begins to dry down. The plant may thin out, just hanging on until days lengthen and the sun strengthens in late March. Then new growth will appear and you can resume fertilizing.

If you keep your hibiscus under a grow light so it adds new leaves vigorously through winter, you can continue fertilizing. However, adjust fertilizer amount and frequency based on a comparison between the plant's rate of growth outdoors and indoors. If it grows half as fast indoors under lights, then cut the fertilizer by half. .


Time to get rid of that mildew-prone phlox? 

You ask if this is the way to go, G.M., after you've tried thinning it, moving it to a place with better air circulation, even applying a fungicide beginning early in the summer to prevent the infection.

A fellow panel member said it best, a few weeks ago as we answered audience questions, "Life is too short and there are too many wonderful plants to try, for you to put up with a loser. Dig it up, compost that plant and move on!"


Green thumbs up

to soil testing before you pronounce your garden to be acid or alkaline. 


Green thumbs down

to assuming drainage is good if the soil surface doesn't puddle. Around buildings, soil is packed, then graded to slope away. Excess water doesn't penetrate, it just runs off. You must dig and fill a hole with water, then see if it empties within twelve hours to know that a bed is well-drained. Where it's well-drained, roots thrive, so plants grow best.


Originally published 10/16/04