The Q&A Archives: Soil in Raised Bed

Question: I have a large flower bed/box, built of brick and attached to my house. It used to have this massive fern and root system that I pulled out over a year ago. I have since attempted to plant seeds, but the only thing coming out of there is a bit of weeds. I'm wondering if I need to completely remove all of the old soil and start fresh. What do you think? And if so, what kind of soil mixture would be best to use to grow seeds of either annuals or perennials? I'm a total newbie to this gardening business!

Answer: It could be helpful to refresh the soil, but consider a couple of other factors as well. You didn't say what seeds or when you planted them. There are two distinct growing seasons in the low desert with different annuals thriving in each season. There's a cool season from approximately the end of September through April. Annuals can be installed from late September to February. Some gardeners prefer to wait until October, as cooler temperatures also help kill off whitefly populations which can quickly decimate plants. The warm season starts with planting in mid to late February. Some plants will make it through the summer's heat; others will end their growth when the heat arrives in May or June.

Other considerations include sun exposure and soil moisture. Planters next to the house are sometimes in ful shade, and many flower seeds and seedlings will need sun. Check your sun exposure and make sure it matches what you are trying to grow. Was the top layer of soil kept uniformly moist? If seeds start their germination process, but then dry out, they don't recover.

As for the soil, if something was growing there before, you mentioned a fern, it's probably okay, so that it doesn't all have to be removed. However, it's always a good idea to add organic matter before each planting season. To improve your soil, incorporate plenty of compost. In sandy soils, compost improves soil fertility, water and nutrient retention. In clay soils, it improves fertility and drainage. Add a 4-6 inch layer of compost and incorporate it about 12-18 inches deep. You can use manure if it is well-aged (6 months) or you won't be planting until it has lost it's heat and decomposed. Each planting season, add more compost. Incorporate a balanced fertilizer (e.g., 10-10-10) or add organic fertilizers such as fish emulsion, bone meal, and seaweed/kelp. Follow package instructions.

After seedlings establish, add a 1-2 inch layer of mulch. Mulch is great to help retain soil moisture, reduce weeds, and as it breaks down it provides nutrients to the soil. Any organic matter can be used as mulch. Try compost, bark, wood chips, straw, or pine needles. I hope this info helps!

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