Spring test: Answers

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1.(c) NPK is the chemical abbreviation for nitrogen, phosphorus and potassium in a fertilizer, respectively. They are the three nutrients that plants use most extensively, and labeling laws require that they be listed on bags of fertilizer. A bag of fertilizer that has 10-5-10 has 10 percent nitrogen, 5 percent phosphorus, and 10 percent potassium.

2.(a) If you deadhead a plant, you remove fading blossoms. Not only does this help to make the appearance of the plant neater, but it also serves to help most plants continue blooming. Of course, you would not want to deadhead any plants that you are saving for their seeds.

3.(c) The C/N ratio refers to the ratio of carbon to nitrogen and is important to consider if you are composting. High carbon materials tend to be brown and dry: straw, dead leaves or sawdust. High nitrogen materials are green and moist, like fresh grass clippings and kitchen scraps. Too much carbon and not enough nitrogen will result in a slowly decomposing pile. But if you have too much nitrogen and too little carbon, you'll get a pile that smells like ammonia.

4.(d) A cover crop does all these things!

5.(b) Thatch is the buildup of grass clippings and other debris that collects at the soil level. A small amount of thatch can help to insulate roots from temperature extremes, but too much will prevent water and air from getting to the plants' roots.

6.(b) Companion plants, when grown together, can actually help each other by providing nutrients the other needs, or by repelling insects.

7.(c) Topdressing means adding a layer of soil or compost to level the surface, to improve the texture of the soil, or to act as a mulch.

8.(d) pH refers to the acidity or alkalinity of the soil and is important to gardeners because it affects nutrient availability to the plants. Based on a scale from 1 to 14, a pH of 7 is neutral, below 7 is acidic and above 7 is alkaline, or basic. Colorado soils tend to be alkaline.

9.(b) Damping off is a fungal disease that causes seedlings to rot at the base and fall over or prevents seeds from sprouting. It is best avoided by using clean containers and sterile potting mix.

10.(a) Green manure is a cover crop grown to improve the soil. It can be winter rye, oats, clover or another legume. It is dug into the soil to feed soil organisms, thus improving soil texture and fertility.

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