Gardening expert answers spring planting questions

The Post's gardening columnist Adrian Higgins answered questions recently in an online chat. Here is an edited excerpt.

Q. What vegetables do well in a part-shade environment? I am interested in putting down an asparagus bed and maybe potatoes also, but the locations I would like to use get some partial shade at different times of the day.

A. I wish I could be more encouraging, but the shade will defeat your aspirations, not to mention your asparagus. The only edible plant that has worked in partial shade for me is redcurrant.

Q. I grow vegetables in raised beds. Each year my tomatoes seem to produce less and look sick sooner. I have rotated the beds that they grow in each year. What would you recommend amending the soil with in early spring? (I dig in lots of compost along with some fertilizer.) Can you offer your best tips for keeping tomato blight at bay?

A. You seem to be the perfect candidate for a grafted tomato. Early blight is best checked by giving the bed a thick mulch of straw. Remove the lower leaves as soon as they show signs of the disease.

Q. I planted three rosebushes. How often should I water them?

A. Roses should be soaked well when transplanted, and then watered only when it gets dry. Water deeply occasionally, so the roots are encouraged to go down. You will drown them in constantly wet soil.

Q. I would love to create a small potted vegetable garden on my brick patio. Most locations would be full sun, and it does get hot. What are some vegetables and herbs that would do well in pots?

A. I would try determinate tomato plants, bush beans (perhaps), dwarf cucumbers, watermelons and pepper plants. The larger the container, the happier everyone will be.

Q. Several years ago I planted two cherry trees — the same kind as the Tidal Basin trees — in a place where we had removed a large pine tree. The area gets plenty of sun. The cherry trees have never really gotten more than a couple of blossoms. Could this be a soil pH thing left over from the pine tree?

A. No. Cherry trees love to bloom. I can only think that they are in too much shade or you didn't get the Yoshinos you thought you did.

Q. The tomatillos I started from seed have gotten very leggy. When it comes time to plant, can I plant them very deep, like tomatoes?

A. You can plant the tomatillo more deeply than it is growing in the pot, but this is a plant that will get leggy and top-heavy no matter what you do, and you should stake it. When you stake tomatoes, etc., it's good to drive in the stake before you plant them, so that you don't spear the plant accidentally. It is much better to train a tomato plant as it grows than try to fix it later.

Q. I always miss the early spring dates to plant carrots, beets, onions, etc. Can you tell me what I should be planting now?

A. You can still sow carrots and beets, no problem. It is too late to sow onion seeds, but you can still put in sets for summer harvest. You can still plant broccoli and cabbage as transplants, and you can still sow lettuce and mesclun. It's too soon for tomato and pepper planting; I would put those in the second week of May. Wait until mid-May to sow beans, cucumbers, squash and corn.

Q. Is it OK to top or cut the topmost bloom on our tomato plants? Last year they kept growing and growing and produced only a little fruit. By the end of summer, they were 6½ feet tall, and we were staking them like mad.

A. I believe some gardeners remove the first flowers so that the plant is still putting all of its energy into growing for its first few weeks. You should also pluck out at least some of the leaf axil suckers as they appear. You may be giving your plant too much nitrogen feed. I would top-dress with a tomato fertilizer and throw in a bit of lime or bone meal for calcium needs.

Q. Is it true that free mulch available through a county is likely to be contaminated with wood borers or other pests or diseases?

A. I don't think so, but it can be awfully trashy. Wood chips are good for paths and long-term compost piles, but they steal nitrogen from growing beds as they break down. Any mulch that smells foul has become anaerobic and may be toxic to plants. It shouldn't be used.

Q. The harsh winter of 2013-14 killed off a sage plant I'd had for about 10 years. I planted a new one last spring, and it was growing phenomenally until midsummer, when it wilted and died in the space of about two weeks. I didn't notice spots or pests, but I thought the young plant was struggling with the heat and just needed watering, so I wasn't looking closely. Any idea what happened and what I could do differently this year?

A. I think you watered it to death. Sage hates heavy, wet soil in summer. I plant mine in a bed that is raised and mixed with gravel, and I mulch the crown with more gravel.

Q. Young squirrels have eaten all the flower buds off my Viburnum carlesii and mohawk, and most of the swelling leaf buds on my small Japanese maple. I have sprayed, alternating with Ropel and hot pepper wax, but they are not deterred. Any other suggestions?

A. I am getting a lot of questions about squirrel damage, not just on viburnum but also on hyacinth flowers and cherry tomatoes. They are a real problem in my garden, eating tulip bulbs even in leaf. I don't know an easy way to thwart them in the city short of trapping them and relocating them (but to where?). Repellents seem better than netting, which can trap birds.

Q. I bought a house, and there is wild garlic growing in the garden and the yard. Should I attempt to use Roundup, or just start digging?

A. If you try Roundup, you should first bash the leaf stalks to break down the waxy barrier on them. Roundup will kill almost anything it touches, so be careful. I might try digging with a fishtail weeder, the sort you use for dandelions.