Answered provided by: Ron Smith, Ph. D., Horticulturist and Turfgrass Specialist at North Dakota State University, Department of Plant Sciences.

My oriental poppies just bloomed last year for the first time in five years. Why wouldn’t they have bloomed before?

There could be many reasons, but some possibilities might be: soil too high in nitrogen; plants not mature enough to produce flowers; if they were divided plantings, perhaps not enough of the root was used in the propagation; or some other factor perhaps in the environment – like temperatures too high for them to thrive, OR, any combination of these things!

When is the best time to treat for slugs? If you had them last year, will you get them again this year?

Almost as sure as death and taxes. There is no point in jumping the gun on getting stuff out this early, except that a good spring clean-up around the area where they were most annoying would go a long way in greatly reducing their number or (hopefully!) eliminating them altogether. Keep in mind that just one slug can beget many more as they are hermaphroditic. If and when they are noted – when the vegetation is actively growing – the safest and one of the most effective methods of control is to place a shallow pie pan of beer at ground level for them to crawl into and die a joyful death – not from intoxication, but simply drowning. To be effective, the pie pan rim must be at ground level — the slugs cannot climb over the edge of the pan.

Can you get the mulch too thick around perennials?

Absolutely. Opt for 2-3” of good organic mulch ­— there are many on the markt. Keep about a one-inch space between the stems of the perennials and the mulch, if possible – especially if there were slug problems in the past. Sorry, stone is mulch not recommended!

Do you need to put new soil into pots every year or can you use the same soil?

Everything gets tired – including potting soil. While there are some records of using the same soil in the pots for many years, it is a better bet for success if the potting soil is changed annually. This can be done in the spring, of course, for outdoor plants, but it is suggested that houseplants get their soil changed in the fall just before bringing them in before a hard frost nips them.

What are some good flowering plants to plant on the north side of my house? I want something other than ferns and coleus.

My absolute favorite comes early in the spring before tree leaf canopies close in­—Virginia bluebells. The purplish/pink flowers are excellent naturalizers in any shady setting. After flowering, they die down for the season, but come backed every year. Another indestructible perennial is the Lily-of-the-Valley, which makes a very good ground cover, and has the little bell-like, white flowers that are back by an almost bullet-proof dense, green foliage. Some annuals, of course, are pansies, (also violas, their smaller cousin), and begonias. Finally, see if you can find some Toad lilies (/Tricyrtis ‘/Tojen’). They are impossible to dislike. Their orchid-like flowers and lush oversized foliage fill in shady areas with  elegance!

What plants do well on the south side of a house that gets a lot of direct sun and heat?

Some of the native ornamental grasses like big or little bluestem simply thrive under such conditions. Potentilla is a nice compact woody plant that likes the direct heat and light. Finally, common daylilies will do well under such conditions, as long as they get ample water.

What perennials are best if you don’t want them to spread too much?

You would need to consult a book for this answer, as the few I’ll recommend will not do justice to the ones I’ll have to leave out. Visit the local bookstore – horticulture section – to get some good, complete selections. Some of my favorite: Bleeding heart, sedum (many varieties), Lady’s mantle, Peony, Astilbe, and Echinacea (they multiply a little).