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Ask the Master Gardener: Celebrate St. Patrick’s Day — or any day — with shamrock houseplants

Shamrocks do well in normal indoor temperatures but cooler nights will prolong blooming. Place them in an area with bright, indirect light.

Shamrock plants.
Potted shamrock plants.
Contributed / Metro News Service

Dear Master Gardener: I would like to purchase a shamrock plant to have as a decoration for St. Patrick’s Day. Will it keep as a houseplant? If so, how do I care for it?

Answer: In March local florists, garden centers and grocery stores sell shamrock (Oxalis) plants to celebrate St. Patrick’s Day. These shamrocks are not the same as those found in Ireland. The word shamrock comes from the Irish Gaelic word seamróg, which means “young clover.” The shamrock that is the Irish symbol is actually a three-leaf clover (Trifolium). The “shamrock” plants you see now have green or purple leaves with three triangular-shaped leaflets and small, five-petaled white flowers. Oxalis are good houseplants. They do well in normal indoor temperatures but cooler nights will prolong blooming. Place them in an area with bright, indirect light. Their roots are shallow and they seem to prefer being pot-bound. While they are flowering, fertilize them every two to three weeks with a liquid houseplant fertilizer at half the recommended strength. An interesting characteristic of many Oxalis plants is the movement of their leaves in response to light levels. Their leaves open in bright light and close on an overcast day and at night.

Dear Master Gardener: How do I know when to start my various vegetable seeds?

Answer: Starting vegetables indoors from seeds can be a rewarding project. It’s a fairly inexpensive way to grow a variety of plants and try different types of vegetables you might not otherwise find. When you are choosing your seeds, check the packet for the number of days until harvest to make sure they will ripen before frost. Many long-season fruits and vegetables must be started indoors in early spring, since we have such a short growing season. Each species has its own requirements, so follow the seed packet or catalog instructions. By mid-March the following can be planted: broccoli, Brussels sprouts, cabbage, cauliflower, head lettuce, and leeks. Mid-March start eggplants and peppers.

Dear Master Gardener: I saw on television that a person can grow a loofah sponge in their garden. Is it true and can it be grown in Minnesota?

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Answer: Yes, it is true! The botanical name for the plant is Luffa aegyptiaca. It is an edible gourd in the cucumber family. It can be grown in Minnesota if you start the seeds indoors or grow it in a greenhouse, as it takes about 90-120 days to reach maturity. Then, you need several more weeks for it to develop its tough inner fibers and dry on the vine before you harvest it, for a total of 150-200 warm, frost-free days. Seeds are available through most seed catalogs. It could be a fun plant to grow as a project with children!

Luffa vines grow very fast and will need a sturdy trellis to keep them off the ground so they don’t rot before you have a chance to harvest them. When the squash-like fruit is still young, it is an edible vegetable that can be eaten raw or cooked, as you would squash or eggplant. However, since the plant grows so fast (about 1-1/2 inches per day) it is difficult to keep up with harvesting. Therefore, you may as well grow them for sponges and let them grow to about 2 feet in length. As they grow larger, they develop tough inner fibers. According to Clemson University, “Luffa sponges are ready to harvest when the skin feels loose and brittle around the hardened fibers inside. To process the sponges, peel the skin off, shake the seeds loose (save some for next year) and dip in a bucket of ten parts water to one-part bleach for about an hour to remove any stains and allow to dry.”

March Gardening Tips

  • Heavy spring snowfall often weighs down evergreen boughs. It’s probably best to just let the snow melt off on its own. If you want to remove it from your evergreens, scoop it off gently rather than hitting the branches, which are still brittle this time of year and prone to breaking.
  • Prune apple and other fruit trees either this month or next, as long as you do it before the buds break and growth begins.
  • March is the month to also prune oak, maple, birch, honey locust, mountain ash, hawthorn, butternut, walnut, ironwood, and beech trees. 
  • Check for black knot, a fungal disease, on chokecherries and other members of the cherry family. Look for hard swollen black galls (tumor-like growths) that form on branches and sometimes on trunks. Make the pruning cut at least 4 inches below the black knot gall. It is best to prune when temperatures are below freezing to prevent black knot spores from infecting the pruning wound. If possible, dip your pruners into a bleach solution between cuts. 
  • By the middle of the month start seeds for annuals such as ageratum, coleus, dusty miller, nicotiana, dianthus (pinks), snapdragons, and verbena. Seeds for alyssum, cleome, moss rose, and salvia should be started at the end of the month. Again, check seed packets for seed starting information as species and cultivars will vary.
  • Move plants you have been overwintering into a sunny window. Cut off dead leaves and stems and start watering. Fertilize when you see new growth.
  • Sharpen pruning tools with a sharpening stone or have them professionally sharpened. 
  • Use a file to sharpen the blades of spades, shovels, trowels, garden forks and other digging tools. 
  • Prune hydrangeas to the first pair of buds above ground or 3 feet up if you want stronger, less floppy stems (as soon as you can find them underneath all the snow!)
  • Prune grapes before new growth emerges.
  • Cut back yellow and red raspberry canes to four to five feet tall before new growth begins.
  • You can begin fertilizing houseplants this month when you see new growth. Fertilize with liquid fertilizer at half-strength.

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.

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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