By Scott Canning, Director of Horticulture and Special Projects
Ah, May! So many pleasures, and so much pressure! The month often starts with at least one unpleasant return to winter. I have seen snow in May more often than not the last five years. Yet by the end of the month, the weather has settled and becomes hospitable to even the tenderest plants. I have learned not to rush the truly heat-loving crops like my beloved tomatoes. Trying to beat the odds on frost is rarely worth it. Even if the tomatoes don’t get frosted dead, exposing them to a few chilly nights in the 30s sets them back badly. They stall and sulk in the garden for a week or more, giving the inpatient gardener the “stink eye,” and you have lost any advantage you expected by planting early. I usually wait until close to the solstice: Vigorous plants tucked into warm soil will flourish, and likely surpass the cold-damaged ones quickly. I have had experienced gardeners recommend the Wall-o-Water, which uses water-filled ribs that act as both a heat sink and a greenhouse. This might get you tomatoes a week or two earlier in the summer, but with added effort and expense. Keep in mind that peas tolerate frost, and are best sown in April, but beans, another legume, resent cold soils and can rot if planted too early
As the weather and soil warms, it is time to plant seeds of annuals, and later in the month, it becomes safe to transplant “starts” into the garden. If you buy them from a greenhouse situation, remember to “harden them off” – take them in on chilly nights, and put them out on warm days in dappled shade, and move them into full sun as they tolerate it. A quick move directly to an outdoor spot in full sun just might “toast” them. Summer-growing bulbs can be planted out even early in the month. They should take a week or two to break dormancy and get above ground, so they offer that bit of insurance against frost. I have a real weak spot for dahlias, which hail from old Mexico and seem well-adapted to New Mexico summers, but they do need supplemental water, especially in June, typically our hottest, driest month. While on the subject of bulbs, it is good practice to dead-head early blooming bulbs like tulips and daffodils after they finish flowering, but don’t remove foliage until it ripens and is dying back on its own – it is photosynthesizing and “recharging” the bulbs for next spring. And those early-blooming shrubs like lilacs and forsythia only get pruned right AFTER they bloom, and only if needed. Otherwise, you will be removing wood that carries next spring’s display. It pains me to see a “mow-and-blow” crew shear these shrubs into balls and drums all summer, never allowing them to achieve what they might have been.
Our moist winter and spring has been a gift to many weeds. Keep ahead of them: They can be unsightly, but more importantly, fast-growing weeds can rob more desirable plants of nutrients and water. And DON’T let them go to seed! The flip side to this advice is the risk of removing self-sowing annuals and biennials like Verbena bonariensis and Clary sage from your garden, so try to learn what these desirable plants look like at the seedling stage.
There is still time to “shop in your own garden,” keeping an eye out for plants that can be lifted and divided to enrich your own garden or to share “over the garden fence.” However, the window of opportunity for this is closing: June is a harsh time to transplant almost anything.
Keep up with your fertilizing chores. Most garden vegetables (and roses!) are particularly heavy feeders and will only perform optimally here if “fed.” Rich garden compost and organic fertilizers that add organic matter and enrich the soil at the same time they provide essential nutrients are the best way to “feed.”
Toward the end of May, it is worth considering moving some of your tougher houseplants outside for the summer. Our climate can be rough on tender houseplants, but for those that can tough it out, the beneficial effects of sun and wind and rain can invigorate them, and mealy bug and spider mite pressure is reduced. Give them a deserved vacation!