Horticulture News: Soil compaction can greatly hinder gardens

By Adam Leonberger, Published:

This has been such a wet spring so far, the ninth wettest April on record in fact, and with a week to go, May has been much the same.

I thought it would be sensible to discuss your soil, or mud in many cases. If you treat your soil well, it will treat you in kind. Specifically, I’m talking about soil compaction. 

Soil compaction creates an unfriendly growing environment for plants and is a serious problem for many home gardeners. However, it is relatively easy to prevent.

Compaction transforms soil into a difficult environment for plant growth by making it harder for roots, water and soil to penetrate the ground. Major causes are working the soil when it is too wet, foot traffic and excessive rototiller use.

To reduce this problem, it is best to avoid working in the garden or walking in it when the soil is too wet. Squeeze a handful of soil and if it forms a muddy ball, rather than crumbling when you open your hand, stay out of the garden area. 

Walk between plants and rows in the garden area to reduce compaction in primary plant growth areas.

Excessive rototiller use destroys soil structure and promotes compaction. When compaction takes place in a dense soil structure, it also makes root growth more difficult.

A little hand hoeing, rather than a rototiller, may be all you need to do to eliminate a few weeds. It usually causes less soil damage than repeated rototilling and is less harmful to the earthworms that help aerate the soil.  You also can use mulch to control weeds instead of tilling. A 2- to 3-inch layer of mulch relieves the pressure of walking on the soil, reducing the degree of compaction.

Reducing compaction

If you find that your soil is already compacted, there are a few things you can do. Incorporate composted organic matter (e.g., manures, recycled yard wastes, etc.) into the top 3-6 inches of soil.  As organic materials decompose, they attract soil organisms that naturally aerate the soil through creation of pore space.  

Another option to alleviate compacted gardens is to plant a cover crop at the end of the season. The roots of the cover crop penetrate the compacted soil and loosen it. In the spring, mow the cover crop and then turn the soil, which additionally loosens the soil and incorporates more organic matter into the soil.  Some cover crops suitable for Kentucky include annual ryegrass, winter wheat and hairy vetch.

Dividing bulbs

And now for something completely different, I’ve been receiving a lot of calls about the best time divide bulbs and perennials. These plants typically need to be divided and thinned every 3 to 4 years, although this varies according to type of plant.

 Spring bulbs can be dug from the ground as soon as the foliage fades. Store the bulbs inside a paper sack or container with dry peat moss or vermiculite placed in a cool area.  This will help to protect them from the hot and dry summer. The bulbs should then be planted in the early fall so that the bulbs have a chance to put down roots before the winter. 

Perennials typically offer a little more flexibility. They can be divided either in fall or early spring, just as new growth is visible. Avoid dividing your plants when the weather is hot and dry, or during times of freezing temperatures.

Perennials can be divided either by digging up the entire plant or by taking pieces from the side of the growing clump. To do this, use a spade to loosen the soil around the plant and gently pull it out of the ground. The plants can also be cut apart using a sharp knife or spade, but pulling apart gently does less damage.

It is important that when the root is separated that each piece has a good root system and several new shoots. Avoid old woody root systems and opt instead for new strong growth. The larger the piece after divided, the sooner the piece will mature. The smaller the division, the longer it will take to mature. Throw away any pieces that may look diseased or weak.

Do not let the newly exposed roots dry out. If you cannot plant them right away, then it is necessary to heel the plants in, either in the ground or in a plastic box that contains soil. Or, you can make new friends and start a garden plant swap with neighbors. 

For more information on this and other horticultural issues, contact the Franklin County Extension Office, 502-695-9035, or Adam.Leonberger@uky.edu.

Source: John Strang, extension horticulture specialist

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