Calabrese and broccoli are cool-season crops, and temperature controls flowering responses; most do not handle heat well. Flower heads can also be malformed or damaged if young transplants sit at temperatures below 40°F (4°C) for a few weeks.

The ideal temperature range for happy broccoli is between 65°F and 80°F (18–26°C). This can be tough to maintain in an enclosed grow room or grow tent unless it is air-conditioned, but normal household temperatures might be adequate.

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Not technically a disease, rather a physical disorder related to water and humidity management and types of light, oedema blisters can cause defoliation.

Oedema occurs when roots take up water faster that the plant can use it. Once water pressure builds up enough in the plant cells, they burst, leaving visible blisters.

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Before you make your selection of which type of pot to use, think about whether you want to reuse the container. A reusable container will be more stable and permanent, but biodegradable seed plugs allow you to plant the entire cell directly into a larger pot or your garden without lifting out the seedling or disturbing its root system.

These biodegradable seed starting cells can be planted directly into a larger container, or into the garden, once the seedling's roots reach the bottom and edges of the plug cell.

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Having the right spectrum of light is not enough to grow healthy plants. You also need the right quantity to fuel photosynthesis.

While accurately measuring light for plant growth might seem complicated—and the fi ne details are beyond the scope of this book—an introductory understanding of how to measure and manipulate light will help take your indoor-growing skills to an entirely new level.

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Coir, or coco fiber, is a more sustainably harvested and renewable alternative to peat moss. Coir mats can be used to propagate, grow microgreens, or line planters.

Some coir can be high in salts, which can interfere with the uptake of certain nutrients, such as calcium. If you plan to use coir as a hydroponic substrate, look for brands that have been washed or composted.

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For most annual and edible seeds, normal germination occurs at optimal soil temperature and moisture levels without any special techniques. You can speed up the germination process (or improve germination rates from older seed stock) if you presprout them, a process called chitting or greensprouting.

Chitting involves soaking the seeds, usually for 24 hours, before you sow them. Moisten some dish towels, paper towels, or newspaper, then set the damp material in a tray, on a plate, or inside a plastic bag. Spread your seed onto the moist surface. Seeds will absorb the moisture and swell, and some will germinate and sprout.

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When you grow plants under only red light, they can put on additional leafy growth, or biomass. This is good for certain crops, such as lettuce. But as plants develop more leaves and other structures, they may not transpire properly or they can stretch, get too tall, or develop oedema (leaf blisters—a common issue in tomatoes grown under only red light) or other problems.

If you grow your plants under only red light for too long, chlorophyll production can stop altogether, causing photosynthesis to cease.

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Newer CMH lamps require less electricity to generate more usable light output, so you can use a lower-wattage lamp than you might with an HPS or an MH lamp. CMHs are thus more efficient than standard MH lamps, and they put out less heat than HPS lamps, which is a great benefit to most home growers.

With a more full-spectrum light output and a 20,000-hour life span, a CMH lamp is a quality all-around HID lighting solution for home gardeners who want to grow a variety of plants indoors without switching lamp types.

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