Deadhead: When an annual plant finishes making seed for the season, it will stop flowering (one of the steps in the seed-making process; see entry on "Pollination") because it has completed its biological mission of reproducing. You can keep the plant blooming longer by plucking off flowers that have passed their prime in appearance but have not yet produced finished seed. Removing those aging flowers is what we (and other people) mean when we recommend that you deadhead the plant.
This is the most basic act of gardening
—planting seeds outside right where you want them to grow. Flowers like sunflowers and nasturtiums are almost always direct-seeded because they come up so quickly and reliably from seeds you sow that there's no need to transplant
seedlings into your garden that were started indoors.
Dividing: You can make two or more plants from one by dividing it, or breaking it into several pieces. Dividing is frequently recommended for certain perennials (see entry entitled "perennial"), like hostas, that have grown too large for their site; if you just want more plants to grow yourself or to share, you can divide almost any perennial that has grown large enough and developed sufficient roots to sustain several plants. "The key to dividing successfully is to make sure that each piece has some top growth and some roots," advises Scott Stiles, horticulturist at Raintree Nursery in Morton, Washington. "And the best time to do it is when it will put the least amount of stress on the plant—that, generally, is when the plant is dormant," Stiles adds.
"Double" flowers: It's all in the petals. Single flowers are like daisies—they have one row of petals around the blossom's center. Double flowers have a second (in some cases third, fourth or more) row of petals completely overlapping the first row; if the secondary petals don't overlap the first layer completely, the flower is called "semi-double."
Foliage: This is simply a way of referring to a plant's leaves. And when we talk about foliage plants, we mean plants that are grown primarily for the appearance of their leaves, like coleus or dusty miller.
Genus/species: Back in the 1700s, a Swedish botanist named Linnaeus devised a system of classifying plants using Latin names so that scientists all over the world could communicate with each other without the confusion caused by using common names that vary from place to place. Today's gardeners benefit from that same system, because when you get information about a plant using its botanical name—which is its genus and species names—you can be sure you're talking about the the exact plant you want. You can think of a plant's genus as its family—actually, in scientific taxonomy family is a broader classification than genus, but for the purposes of our explanation the concept of the genus as the family is very sensible.
So, for example, lilies belong to the genus Lilium, and within that genus there are thousands of relatives called species, like Lilium tigrinum (commonly known as the Tiger lily) and Lilium longiflorum (sometimes called the Trumpet lily). They are all lilies, but they differ somewhat in color, height of the plant, etc. Plants that belong to the same genus will have many similar characteristics, but those in the same species will have even more in common. Within each species there can be many cultivars, or what we call varieties (see entry on "cultivars" above); plants of the same variety will have virtually identical traits.
The process of splicing parts of two or more plants together to make one plant is known as grafting. The reasons for making these botanical Frankensteins is to get desirable characteristics from each of the original plants into the resulting plant. Many of the most beautiful roses, for instance, have roots that are susceptible to diseases
or cannot survive cold winters, but gardeners can still grow those roses because nurseries graft the attractive tops of the bushes onto more durable roots. And you don't need to be a mad scientist to do this yourself—the techniques are simple, you don't need special tools to do it and if you choose compatible plants the prospects for success are very high.