Wednesday, May 27, 2020
May 27, 2020

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Gardening with Allen Wilson: Plant covers, plastic mulch speed growth of warm weather vegetables


In last week’s column, you mentioned using plant covers and plastic mulch to speed growth of tomatoes and other warm season vegetables. Could you explain how they speed growth?

Plant covers and plastic mulch speed growth of warm season vegetables by creating warmer air temperatures and soil temperatures around the plants. Both have additional benefits.

Warm vs. cool

It is easy to differentiate between warm and cool weather vegetables. If you eat the fruit of the vegetable, it is a warm season vegetable. Two exceptions are potatoes and sweet potatoes which are both warm season vegetables.

If you eat the root, stems, leaves or flower buds, it is a cool season vegetable. The two exceptions are peas and fava beans.

Cool season vegetables like our cool night temperatures. Their maturity ratings tend to be accurate here. They are also frost-tolerant and can usually be planted up to six weeks before the average last frost date.

Warm season vegetables grow more slowly in our climate with cool night temperatures and day temperatures. You normally need to add 15 days to maturity ratings.

Row covers

Clear polyethylene plastic is often used to create plant covers or tunnels for plants using metal hoops for support.

Lightweight spunbonded polypropylene row covers need no support. They float on top of the plants. They are rain-permeable to allow for easy irrigation.

Both types of row covers trap radiant heat, which increases the rate of plant growth. They also protect against insects and provide 2 to 4 degrees of frost protection.

Some types of floating row covers can be used for cool season crops strictly for insect protection.

Plastic mulch

Several types of plastic mulch can be used to warm the soil and create somewhat warmer air temperature, especially if used in combination with row covers. Black, red and solar plastic mulch also prevent weed growth by blocking light. Black plastic mulch absorbs sun energy and transfers the heat to the soil where it touches. Red and solar plastic mulch allow radiant waves to penetrate, warming the soil faster than black plastic while preventing the shorter light waves that stimulate weed growth. The weed prevention quality of plastic mulch is sometimes of greater value than its heating benefit.

The widest selection of row cover and plastic mulch supplies may be found online at companies like and