Gardening: Biennials shoot up and flower in second year

Q. What kind of plant is this that is growing in our backyard? It came up voluntarily and has a very large stem and has grown to about 6 1/2 feet tall. How do we get rid of it?

A. The plant is a biennial plant called commonly as great burdock (Arctium lappa). A biennial plant grows for two years. The first year, the biennial grows leaves that hug the ground in the form of a rosette and develops a large tap root. It does not get very tall the first year. It overwinters as an unnoticeable large fleshy root.

The second year, the plant grows upward with all the stored energy in the tap root and can reach up to 8 feet tall if the soil is rich in nutrients. It flowers and produces large amounts of 1/4-inch seed. It will die naturally at the end of the second year. But you must prevent it from producing seeds as they can produce many plants not very far from where the mother plant grew. You will need to cut the plant and remove most of the root as well. Make sure to remove as many seeds as you possibly can. Using an herbicide will cause the plant to die back, but then it will form many stems determined to produce more seed.

Many gardeners are familiar with Canada thistle (Cisium arvense), a biennial troublesome weed that is very persistent in producing seed.

Q. We have a full-grown southern magnolia tree we planted many years ago, which has gradually lost most of its leaves this year. It was in the middle of our backyard (east of the house) and we are wondering if the harsh winter killed it. The leaves started falling off prematurely; big green leaves first, then even young green ones. Then the remaining leaves all turned brown and brittle and have been falling till the poor tree is almost barren of leaves. For future reference, what should we have done?

A. Southern Magnolia or Bull Bay (Magnolia grandiflora) is hardy to plant zone 6. We are on the edge of plant zone 5 and 6 which means you will have to be very attentive to winter weather conditions. You must give it the correct location and soil conditions. The Southern Magnolia needs to be grown in partial shade and can tolerate as low as three hours of sunlight per day. The location must also be protected from winter winds and sunlight. The soil should be rich, porous, well-drained and slightly on the acid side.

There are many cultivars of the Southern Magnolia. For the latest research and information of which varieties are best for hardiness, contact: Secrest Arboretum, 1680 Madison Ave., Wooster, Ohio 44691.

This story was originally published July 16, 2015 at 5:00 AM with the headline "Gardening: Biennials shoot up and flower in second year."