Potting Dahlias and Other April Gardening Tips

By: Charlie Nardozzi, Horticulturist and
Leonard Perry, UVM Extension Horticulturist

Potting up dahlia tubers inside to give them a jump on the season, cutting back ornamental grasses, and removing straw from strawberries are some of the gardening activities for this month.

Get flowers sooner by potting up dahlia tubers and growing them indoors until it’s warm enough to plant them outside. Pinch the growing tips when they get 6 inches tall to keep the growth short and stocky for easier transplanting into the garden.

If you left your ornamental grasses intact last fall, you can go ahead and prune them back to a height of about 6 to 10 inches. If you remove the old growth before new growth starts when temperatures warm, you won’t risk damaging new sprouts. Add prunings to the compost pile.

Check strawberry plants twice a week for signs of new growth. As soon as you see sprouts, remove the straw mulch and spread it in the rows to help control weeds. A topdressing of an inch or two of compost will give plants a boost.

Likewise, if you are growing garlic and mulched it with straw over winter, remove it at the first signs of growth appearing at the soil surface.  This will allow the sun to warm the soil more quickly, and shoots to not stretch under the straw as they seek the light.

When planting large containers for the deck or patio, save on soil by creating a false bottom. Most of the plants you’ll use don’t need more than about a foot of soil depth for their roots, so put some empty plastic soda or water bottles in the very bottom, then cover with landscape fabric or a piece of cardboard cut to fit to keep the soil in place. Or use small plastic pots upside down to take up some space before filling the planter with soil.

Woody perennials differ in the way they should be cut back in spring. If butterfly bush has died to the ground, cut the dead stems to the ground. Otherwise just shorten them by about one third. You should wait until you see signs of growth (green buds) to know if stems are living.

Cut back Russian sage, rue, and artemisia to about 8 to 12 inches from the ground. Don’t prune lavender until new growth appears and then just shorten the stems by about one-third. Heather should be lightly pruned to remove the old flowers and the tips of the shoots, but don’t cut back to hard brown wood, stay in the green and softer most recent growth.

Don’t  prune spring-flowering plants such as lilacs and forsythia. The latter need to be pruned later this year, after they finish blooming. Prune evergreens just after they begin growth, usually in May, by using fingers to shorten the new soft growth called “candles”.

April is the time to start many annual flower and vegetable seedlings. As a rule of thumb, sow your seeds indoors about six to ten weeks before you plan to transplant them outdoors. Higher temperatures will speed germination and growth over cooler growing areas, so adjust dates accordingly by consulting the seed packet instructions. A soil-less potting mix is best.

If you haven’t done a soil test in recent years (or ever), now is a good time.  The results will tell you what to add to the soil, and how much, prior to the growing season.  If the soil acidity (pH) is off, this may cause nutrients to not be available to your plants.  A soil test aids you in only adding what is needed, and not too much fertilizer (particularly nitrogen and phosphorus) which can run off into and pollute waterways. Check your local garden store or Extension office for soil test kits, or find details online (pss.uvm.edu/ag_testing/).

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Charlie Nardozzi is a nationally known horticulturist, author, gardening consultant, and garden coach (CharlieNardozzi.com).  Distribution of this release is made possible by New England Grows– a conference providing education for industry professionals and support for Extension’s outreach efforts in horticulture.