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Ask the Master Gardener: Transplanting potted tulips to gardens can be tricky

Unfortunately, potted bulbs rarely bloom the following season since they didn’t grow outside in full sun, but it can still be a fun experiment.

Tulips in a garden.
Tulips are a bit more finicky than daffodils or crocus, and some varieties only rebloom for a year or two.
Contributed / Metro Newspaper Service

Dear Master Gardener: I was given a pot of beautiful tulips. Can I plant them outside and enjoy them again next year?

Answer: You can try. Tulips are one of the first harbingers of spring and can provide a big splash of color soon after the snow disappears. Tulips are a bit more finicky than daffodils or crocus, and some varieties only rebloom for a year or two.

Tulips have to go through an extended cold period before blooming. Our winters obviously provide that, which is why tulip bulbs are planted in the fall. You have a couple of options when you have potted tulips. Cut off the flowers as they fade so the plant won’t make seeds, but leave all the foliage attached so the energy can move down into the bulb. Plant the bulbs in rich, well-drained soil as soon as possible. Mark the spot so you don’t forget they are there. Alternatively, let the leaves wither after blooming, then remove the bulbs from the pot, cut off the dry foliage, and use a soft brush to get the bulbs as clean as possible. You can leave the roots attached. Place the bulbs in a paper sack and store in a cool, dark, dry place over the summer. In the fall, plant the tulips as usual. Unfortunately, potted bulbs rarely bloom the following season since they didn’t grow outside in full sun, but it can still be a fun experiment.

Dear Master Gardener: Is there anything I can plant under a black walnut tree that it won’t kill?

Answer: Toxicity of black walnut trees (Juglans nigra) is one of the most persistent gardening myths. A wonderful tree that produces edible black walnuts and beautiful lumber should be prized. Instead, going back to Pliny the Elder in the first century AD, this poor tree has been accused of poisoning anything that dares to grow nearby. The chemical juglone gets the blame, although the tree only produces the non-toxic precursor hydrojuglone. Research shows that although in the laboratory a negative effect may be demonstrated, in nature it would be almost impossible for toxic levels to develop and move to the roots of nearby plants. Leaves, twigs, and wood chips do not contain juglone. Many publications still support the toxicity myth, citing two papers as evidence, but a fact sheet published by Washington State University Extension finds that one of the papers never existed and the second one is no longer available. There is, however, ample evidence of success with understory growth and garden beds. Bear in mind that your plants will be in heavy shade, so ferns, hostas, and other shade lovers would be good choices.

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Dear Master Gardener: I’m ready to plant my containers and window boxes. Do I have to clean them and replace all the potting soil?

Answer: Probably not. If you had plant disease problems last year, then you need to dump everything out, sterilize the containers with a weak bleach solution, and use new potting mix. Remember, no rocks or pool noodles or milk jugs in the bottom — they create a perched water table that paradoxically creates bad drainage. If you didn’t have disease problems, then just add enough new mix and amendments to fill the pot. Some slow release fertilizer will keep things going strong.

Dear Master Gardener: I love Colorado Blue Spruce and have the perfect spot for one. I don’t see as many of them as I used to. Is there a reason?

Answer: Unfortunately, Colorado Blue Spruce trees (Picea pungens) are no longer recommended to be planted in Minnesota by the University of Minnesota. As beautiful as they are, this long time favorite is very susceptible to Rhizospaera needle cast, a fungal disease which causes the needles to turn brown and fall off. Another fungal spruce disease, Cytospora canker, attacks individual branches, not killing the tree but ruining its shape as these dead branches are pruned out. There are some new dwarf blue spruce cultivars, like “Fat Albert,” and some concolor firs and white spruce varieties that have blue-green needles that may work for you.

Dear Master Gardener: What is the difference between bags of garden soil, potting soil, and potting mix? What should I use in my containers?

Answer: Confusing isn’t it? Garden soil is pretty much topsoil with a few additives like fertilizer. It is the heaviest choice and is intended to be used in your existing outdoor garden. It’s too heavy to be used in containers because it will compact and hold too much water. Potting soil is a bit lighter because it contains more organic matter like peat, compost, or coir (the ground up brown husks of coconuts). There may also be some inorganic additives like perlite or vermiculite. This can be used in containers, but it is not considered sterile. It holds water well and doesn’t break down quickly because it contains soil. Potting mix is the lightest option and because it doesn’t contain any “dirt,” it’s considered sterile and works the best for starting seeds. Mixes consist mostly of peat and coir, bark, perlite or vermiculite and usually some fertilizer. Potting mix allows good aeration of the roots and water drains easily. One problem can be that when peat dries out completely it becomes hydrophobic and is difficult to get wet again. The moisture control mixes contain more coir which holds water. For my outdoor containers I like to create my own mix by combining some of all three types and adding perlite, worm compost, and coir to keep things fluffy and damp.

You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A Master Gardener will return your call. Or, emailing me at umnmastergardener@gmail.com and I will answer you in the column if space allows.

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University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.

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