Parsnips grow in zones two through nine. However, parsnips are a winter vegetable. Their flavor is not fully developed until they have been exposed to near freezing temperatures for two to four weeks. This changes the starch into sugar and gives them a unique flavor. If you live in an area that doesn’t have much of a winter, you may find that this starch transformation does not happen.
Because parsnips are root vegetables, it is important to prepare their bed carefully. Till the soil down to a depth of twelve to fifteen inches. Cover the soil with three inches of compost and till it in. This not only loosens the dirt so the parsnips can grow in it easily, it also improves the drainage of the bed and fertilizes the parsnips.
Parsnips are picky about germination. Only fresh seed germinates well at all. You will need to buy seed each time you plant. You can save the seed from a few plants you let bloom and set seed the previous summer, but packaged seeds left over from last year just won’t do.
The soil temperature must be at least 46 degrees F for parsnips to germinate, but they do far better when it is 50-54 degrees F. Parsnips can take a full month to germinate, so don’t lose hope after a couple of weeks without any seedlings poking out of the ground.
Sow the parsnip seeds one to two inches apart. Rows should be spaced sixteen inches apart. The seeds should be planted one half an inch deep. An easy way to know where you planted the row of parsnips is to plant something that grows fast, like radishes, between the parsnip seeds. The radishes come up quickly to you can see the rows and know where to weed. The radishes are ready to harvest about the time the parsnip seedlings appear.
When the parsnips appear, you will need to do some thinning to get good roots. Start by removing every other plant when they are an inch or two high. Every two weeks or so, repeat this until there is six to ten inches between the parsnip plants.
It is important to control weeds in your parsnip patch. Parsnips do not compete well with weeds, so if you do not regularly remove the weeds, you will not get much of a crop.
Normally, vegetables require a lot of water to produce good plants. In this case, however, it is important to water sparingly so that the parsnip roots grow long and strong by searching for water. Only water one inch a week.
Parsnips are vulnerable to aphids, leaf miners, carrot rust flies, and parsnip canker. Most varieties of parsnips are resistant to parsnip canker. Swallow-tail butterflies also lay their eggs on parsnip plants and their caterpillars can be a problem. Hand picking the caterpillars is usually sufficient to control them.
Parsnips mature in about sixteen weeks. They should be left in the ground for a few frosts but removed before the ground freezes.