Before planting perennials you've ordered from mail-order sources, remove any packing medium and carefully untangle roots. Dig a hole about twice the width of the rootball and build a cone of soil in the center. Set the roots atop the cone, then refill the hole, burying roots to just below where new foliage emerges.
Early in the month, sow in the garden seeds of cool-season veggies such as carrots, chard, and spinach. Late in the month, sow seeds of warm-season crops such as beans, corn, and squash; set out seedlings of eggplant, peppers, and tomatoes.
It's not too late to plant drought-tolerant shrubs like ceanothus, cotoneaster, Fremontodendron, manzanita, and rosemary. Dig planting holes the same depth as the rootball and at least twice as wide. Unless your soil is extremely sandy, it's usually better to plant in unamended soil. After planting, add a 2- to 3-inch layer of mulch around the plants, keeping it about an inch away from trunks and stems.
Prized for their rich flavor, heirloom tomatoes such as 'Brandywine' are becoming more widely available as seedlings in retail nurseries. If you can't find the variety you're looking for, check out Laurel's Heirloom Tomato Plants; owner Laurel Garza sells organically grown seedlings of 200 heirloom varieties. For cooler coastal areas such as San Francisco, she suggests 'Carmello', 'Goose Creek', and 'Sunset's Red Horizon'. For warmer regions of the Bay Area and Sacramento, she likes 'Eva Purple Ball' and 'Paul Robeson'.
All Citrus can be planted this month. Don Dillon, owner of Four Winds Growers, suggests the new seedless mandarin ‘Gold Nugget’ for warm-summer areas. Coastal gardeners might try fragrant fingered citron (‘Buddha’s Hand’), which makes delicious candied fruit. Find trees at fourwindsgrowers.com or your local nursery.
As you groom the garden, add trimmings to the compost pile along with fruit and vegetable waste. To help the plant material break down faster, chop or shred it into smaller pieces, then toss it onto the pile, alternating 6-inch layers of brown material (dry leaves, straw, and tree prunings) with 6-inch layers of green matter (fresh lawn clippings and weeds without seed heads). Keep the pile as damp as a wrung-out sponge and turn it frequently.
Tend flowering shrubs. After azaleas, camellias, and rhododendrons finish blooming, remove spent blooms, taking care not to damage the new growth just beneath them. Feed the plants with a fertilizer especially developed for acid lovers.
As temperatures rise, increase the frequency of irrigation. Deep-water established plants often enough to prevent wilt and promote deep rooting, but don't water more than necessary (check soil moisture around roots with a soil auger or by digging down with a trowel).
Eliminate mosquito breeding sites by draining excess water from pipes, gutters, buckets, plant containers, and anywhere else that water may stand or collect. Stock ponds and fountains with mosquitofish (Gambusia affinis), which eat mosquito larvae and are available from nurseries that sell water plants. Many county mosquito- and vector-control departments also provide free mosquitofish.